Detailed modern data on the structure and vital activity of cells and tissues are presented, all cellular components are described. The main functions of cells are considered: metabolism, including respiration, synthetic processes, cell division (mitosis, meiosis). A comparative description of eukaryotic (animal and plant) and prokaryotic cells, as well as viruses, is given. Photosynthesis is considered in detail. Particular attention is paid to classical and modern genetics. The structure of tissues is described. A significant part of the book is devoted to the functional human anatomy.
The book is intended for students of schools with in-depth study of biology, applicants and students of higher educational institutions studying in areas and specialties in the field of medicine, biology, ecology, veterinary medicine, as well as for school teachers, graduate students and university professors.
Approved by the Ministry of Education and Science of the Russian Federation.
6th edition, revised and enlarged.

User comments:

User #Z8XRZQ3 writes:

Excellent textbook! The first volume of three "Anatomy" (and there is also "Zoology" and "Botany").
Not an encyclopedia, not a reference book, not an atlas, but as a textbook - wonderful! Everything is detailed, understandable; according to this textbook, among other things, reports can be written.
Only the scarcity of the content and the weight of the book upset me, I am delighted with the rest!

manual recommended by the leading medical universities in Moscow as one of the best for preparing for exams.
A trilogy that gives a complete picture of the living organisms that inhabit the planet: from the smallest cell to the most complex mechanism - man.
Volume ANATOMY examines in detail a person, his structure, genetics, psychology. Each topic is provided with detailed descriptions, rich illustrative material (black and white), at the end of the topic - questions for self-control.

I liked the book very much! Excellent content, both for schoolchildren and medical students!

Editor: Borovikov A. A.

Publisher: Phoenix, 2017

Series: Applicant

Genre: Auxiliary materials for students, Reference books for schoolchildren

The handbook presents modern data on the structure, functions and development of living organisms, their diversity, distribution on Earth, relationships with each other and with the environment. The problems of general biology (structure and function of eukaryotic and prokaryotic cells, viruses, tissues, genetics, evolution, ecology), functional human anatomy, physiology, morphology and taxonomy of plants, as well as fungi, lichens and slime molds, zoology of invertebrates and vertebrates are considered.
The book is intended for schoolchildren and applicants entering universities in areas and specialties in the field of medicine, biology, ecology, veterinary medicine, agronomy, animal science, pedagogy, sports, as well as for school teachers. Students can also use it with success.
8th edition.

User comments:

User Egor Morozov writes:

"Biology for university applicants"Kryzhanovsky V.K., candidate of biological sciences, who taught at the Sechenov MMA, will be very useful for students in preparing for classes in biology, as well as in botany and human physiology. The manual analyzes and describes in detail many biological processes

The most capacious presentation of an in-depth biology course. The material is presented logically and consistently, at a high theoretical level. The book is not suitable for those who need "something just to pass": working with this manual requires a certain theoretical background and knowledge of biological terminology. The manual is not limited to the school curriculum, but provides a theoretical basis at the level of the basics of the university course. In some cases, the material turns out to be redundant in comparison with the requirements ...

The most capacious presentation of an in-depth biology course. The material is presented logically and consistently, at a high theoretical level. The book is not suitable for those who need "something just to pass": working with this manual requires a certain theoretical background and knowledge of biological terminology. The manual is not limited to the school curriculum, but provides a theoretical basis at the level of the basics of the university course. In some cases, the material turns out to be redundant in comparison with the requirements of the USE program. For example, the taxonomy given in the book is closer to that adopted in modern biology, but wider than that offered in the school course. The illustrations are black and white, but in most cases accessible to perception.
The manual is addressed mainly to those students who in the study of the subject are not limited to school textbooks.

An excellent guide to preparing for college. It describes in detail all sections of biology, but a little in a difficult language for a beginner. But for those who want to improve their knowledge and reach a different level in the study of biology, this collection is ideal. Also, this collection will be useful to you at the university.

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G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M.: OOO

"Publishing house "ONIX 21st century". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 2 G.L. BILICH, V.A. KRYZHANOVSKY

MOSCOW

"ONYX 21st century"

G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 3 UDC 57(075.3) BBK 28ya729 B61

Reviewers:

Doctor of Medical Sciences, Professor, Academician of the Russian Academy of Natural Sciences L.E. Etingen; Doctor of Biological Sciences, Professor A.G. Bulychev Authors: Bilich Gabriel Lazarevich, Academician of the Russian Academy of Natural Sciences, Vice-President of the National Academy of Juvenology, Academician of the International Academy of Sciences, Doctor of Medical Sciences, Professor, Director of the North-West Branch of the East European Institute of Psychoanalysis . Author of 306 published scientific papers, including 8 textbooks, 14 manuals, 8 monographs. Kryzhanovsky Valery Anatolievich, Candidate of Biological Sciences, Lecturer at the Moscow Medical Academy. THEM. Sechenov, author of 39 published scientific papers and two textbooks.

Bilich G.L.

B61 Biology. Full course. In 3 volumes. Volume 1. Anatomy / G.L. Bilic.

V.A. Kryzhanovsky. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

ISBN 5-329-00375-X ISBN 5-329-00601-5 (Volume 1. Anatomy) Detailed modern data on the structure and vital activity of cells and tissues are presented, all cellular components are described. The main functions of cells are considered: metabolism, including respiration, synthetic processes, cell division (mitosis, meiosis). A comparative description of eukaryotic (animal and plant) and prokaryotic cells, as well as viruses, is given. Photosynthesis is considered in detail. Particular attention is paid to classical and modern genetics. The structure of tissues is described. A significant part of the book is devoted to the functional human anatomy.

The book is intended for students of schools with in-depth study of biology, applicants and students of higher educational institutions studying in areas and specialties in the field of medicine, biology, ecology, veterinary medicine, as well as for school teachers, graduate students and university professors.

UDC 57(075.3) BBK 28ya729 ISBN 5-329-00375-X ISBN 5-329-00601-5 (Volume 1. Anatomy) © G. L. Bilich, V. A. Kryzhanovsky, 2004 © ONIKS Publishing House LLC 21st century", 2004

–  –  –

electronic table of contents electronic table of contents

Introduction

Table 1. Hierarchical levels of the body structure

CELL THEORY

CHEMICAL ORGANIZATION OF THE CELL

Table 2. Characteristic features of prokaryotic and eukaryotic cells.

21 Fig. one.

General amino acid scheme:

Rice. 2. Fragment of a polypeptide (according to N. A. Tyukavkina and Yu. I. Baukov, with changes)

Rice. 3. The general formula of triacylglycerol (fat or oil), where R1, R2, R3 are fatty acid residues

Table 3. Composition of nucleic acids

The structure of nucleic acid molecules:

Spatial structure of nucleic acids:

STRUCTURE OF THE ANIMAL CELL

BIOLOGICAL MEMBRANES

Table 4. Note: this table is generalized for plant and animal cells

The structure of a biological membrane:

Phosphatidylcholine phospholipid molecule:

surface complex

Surface complex:

Scheme of functioning of transport proteins:

Scheme of passive transport along an electrochemical gradient and active transport against an electrochemical gradient:

Rice. 12. Electrochemical proton gradient. Gradient components:........ 32 Active transport

Scheme of the functioning of carrier proteins:

(Na*K*)ATPase:

Glycocalyx:

Intercellular connections

Intercellular connections:

microvilli

Microvilli and stereocilia:

Pore ​​complex:

Surface structures of the core:

The nucleus and perinuclear region of the cytoplasm:

Chromosomes and nucleoli

DNA packaging levels in a chromosome:

The structure of the nucleolus:

Karyotype

Rice. 24. Human karyotype (healthy male)

CYTOPLASM

Hyaloplasm

Organelles

General Purpose Organelles

NON-MEMBRANE ORGANELLES

CYTOSKELETON

microtubules

Microtubule structure:

Intermediate filaments

Intermediate filaments

Rice. 26. Intermediate filaments in a cell

Microfilaments

Table 5. Types of intermediate filaments

Actin microfilament:

CELL CENTER

Cell Center:

G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 5 RIBOSOMES

Ribosome:

MEMBRANE ORGANELLES

MITOCHONDRIA

Table 6. Morphofunctional organization of mitochondria

Mitochondria:

Giant mitochondrion:

ENDOPLASMIC RETICULUM

Endoplasmic reticulum:

Rice. 33. Various forms of the Golgi complex (according to B. Alberts et al. and according to R.

Krstichu, with changes)

Scheme of the secretory pathway and membrane renewal:

Scheme of the GERL complex (Golgi, Endoplasmic Reticulum, Lysosomes):

Rice. 36. The scheme of movement of the contents of the cell in containers ("shuttles"): .... 57 LYSOSOME

Rice. 37. Scheme of the structure and functioning of lysosomes

PEROXISOMS

Peroxisome:

Special organelles

cilia and flagella

Eyelash:

Flagellum (flagellum)

Inclusions

INTEGRATED CELL REACTIONS

ENDOCYTOSIS

pinocytosis

Receptor-mediated endocytosis:

PHAGOCYTOSIS

Phagocytosis:

INTRACELLULAR BIOCHEMICAL REACTIONS

PROTEIN SYNTHESIS

Rice. 42. Scheme of protein synthesis (explanations in the text)

Table 7. Genetic code

MAIN REACTIONS OF TISSUE METABOLISM

Entropy

Three stages of catabolism:

Rice. 44. The general scheme of metabolism in the cell and the role of CoA in it (according to A.

Lehninger, with modifications)

Stages of breakdown of glucose and fatty acids in the cell:

Rice. 46. ​​Reactions of glycolysis.

Rice. 47. Ways of using PVC

Rice. 48. Fatty acid oxidation cycle, the stages of which are sequentially catalyzed in the mitochondrial matrix by four enzymes.

Citric acid cycle

Rice. 49. Citric acid cycle (Krebs cycle)

Rice. 50. Electron transfer chain from NADH to O2

EXOCYTOSIS

Rice. 51. Exocytosis (explanations in the text)

WAYS OF PERCEPTION AND TRANSMISSION OF INFORMATION BY A CELL

LIFE WAY OF CELLS

CELL CYCLE

Cell cycle:

cell cycle

Interphase

Changes in the cell center during the cell cycle:

Telophase

Meiosis:

Rice. 55. Crossover scheme

Pachinema (Greek pahys - thick)

Metaphase-I

In anaphase-I

In telophase-I

Table 8. Comparative characteristics of mitosis and meiosis

Table 8 continued

G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 6 Interphase-II

STRUCTURE OF THE PLANT CELL

A modern (generalized) scheme of the structure of a plant cell, compiled according to the data of an electron microscopic study of various plant cells:

CELL WALL

Rice. 57. The course of cytokinesis in cells of higher plants with a rigid cellular structure

Rice. 58. An electron micrograph showing cellulose fibers in individual layers of the cell wall of a green seaweed - Chaetomorpha melagonium

Rice. 59. Scheme of a possible connection of the two main components of the primary cell wall - cellulose microfibrils and matrix.

Scheme of the structure of the cell wall:

Simple pores in the shells of stony cells from walnut seed rind:

Scheme of the structure of a pair of bordered pores:

Rice. 63. Plasmodesmata.

A section of the membranes of three adjacent cells at medium magnifications of an electron microscope (schematized):

PLASTIDS

Plastids are organelles unique to plants........ 104 Chloroplasts

The structure of the chloroplast:

Different types of plastids:

Reproduction and development of plastids

Rice. 66. Ontogeny of chloroplasts

The evolution of plastids.

Formation of vacuoles:

Functions of vacuoles

Different state of plasmolyzed cells in Allium sera onion skin cells:

PLANT CELL INCLUSIONS

starch grains

Starch grains:

Aleurone grains in cells from the nutrient tissue of the castor seed, from which some of the oil has been extracted:

Lipid drops

Rice. 71. Crystals and accumulations of mineral salts in cell sap: .................. 114 Questions for self-control and repetition

STRUCTURE AND FUNCTIONING OF A PROKARYOTIC CELL

MORPHOLOGY OF MICROORGANISMS

Various prokaryotic cells:

Rice. 73. Schematic representation of the structure of a bacterial cell: .................. 116 Table 9. The composition of lipids in cell membranes of eukaryotes and prokaryotes .............. ..... 117 Fig. 74.

The structure of the bacteriorhodopsin molecule and its location in the lipid bilayer:

Table 10. Composition of membranes of Micrococcus luteus (lysodeikticus) and phototrophic bacteria

cell wall

Cell wall of a bacterium:

Areas of adhesion in Escherichia coli:

Rice. 77. Scheme of the structure of the cell wall of gram-negative bacteria: .............. 121 Capsules, mucus, vaginas.

mobility of prokaryotes.

Scheme of rotation of the flagellum:

Rice. 79. Structure of the spiral filament of the flagellum

Diagram of the structure of a spirochete:

Chemotaxis mechanism:

Rice. 82. Structure of fimbria (drank)

Cytoplasm

Other prokaryotic organelles.

Gas vacuoles (aerosomes)

Carboxysomes

Intracellular storage substances.

resting forms.

Resting forms of prokaryotes:

G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 7 Fig. 84. The process of sporulation (A-D) and the structure of mature spores (E): ............... 129 Table 11 Comparative characteristics of the processes during spore formation and germination of spores

Schematic representation of contacts in different representatives of cyanobacteria (A) and microplasmodesmata in filamentous forms (B):

The genetic apparatus of prokaryotes

ppasmid DNA conformation:

Rice. 87. Sticky ends and formation of a circular plasmid

Questions for self-control and repetition

PHYSIOLOGY OF MICROORGANISMS

The chemical composition of a microbial cell

Dry residue

Table 12. The content of the main elements of microorganisms

Table 13 Content of macromolecules in Escherichia coli cells

Nucleic acids

Carbohydrates.

Metabolic processes in a microbial cell

Table 14. Localization of functions in eukaryotic and prokaryotic cells

End of table 14

Table 15. Classification of organisms by energy sources and reducing equivalents

Rice. 88. Electron transfer by various ferredoxins

Table 16. Differences between assimilation and dissimilation nitrate reduction

Table 17 Nutrient Sources for Microorganisms

Active transport of sugars into the bacterial cell:

Rice. 90. Channel-forming ionophore (1)

energy exchange

Rice. 91. Scheme of the oxidative pentose phosphate pathway

Rice. 92. Entner-Dudorov way

Rice. 93. Glyoxalate cycle (according to A. Lehninger, with changes)

Action of ATP synthetase:

Anaerobic respiration.

Rice. 95. Proton-motive force in aerobes (A) and anaerobes (B) (according to B. Alberts et al., with changes)

fermentation

Rice. 96. Homofermentative lactic acid fermentation

Table 18. Lactic acid fermentation

Table 19

propionic acid fermentation:

Table 20. Clostridia, differing in the nature of fermentation

Rice. 99. Butyric fermentation

Formic acid fermentation

Photosynthesis

Table 21. Photosynthetic apparatus of prokaryotes

Chemosynthesis

Rice. 100. Electron transfer chain during nitrite oxidation in Nitrobacter winogradskyi

iron bacteria

Sulfur bacteria

Rice. 101. Ways of electron transfer in thionic bacteria during the oxidation of various sulfur compounds

GROWTH AND REPRODUCTION OF MICROORGANISMS

Bacterial Growth Curve:

Questions for self-control and repetition

The structure of viruses.

Schematic representation of the structure of the main human and animal viruses:

Life cycle of viruses.

The first stage is the adsorption of virions on the surface of the target cell.

–  –  –

A generalized scheme of the main stages of the development cycle of an oncogenic RNA genomic virus:

Rice. 105. Penetration of oncoviruses into the cell

The second stage consists in the penetration of the whole virion or its nucleic acid into the host cell.

The third stage is called deproteinization.

During the fourth stage, on the basis of the viral nucleic acid, the compounds necessary for the virus are synthesized.

In the fifth stage, the synthesis of the components of the virus particle takes place.... 175 Pic. 107. Scheme of phage reproduction accompanied by cell lysis .............. 175 Classification of viruses

Schematic representation of a spherical virus:

Table 22. Classification of viruses (DNA ~ RNA)

Rice. 109. Scheme of the structure of a phage particle

Morphological types of bacteriophages:

The meaning of viruses

Questions for self-control and repetition

epithelial tissue

Glandular epithelium (gland)

Diagram of the structure of epithelial tissue:

Diagram of the structure of exocrine and endocrine glands:

Table 23. Characteristics of different types of epithelium

Table 23 continued

Table 23 continued

End of table 23

The structure of the goblet cell:

exocrine gland

Types of exocrine glands:

CONNECTIVE TISSUE

Rice. 115. Scheme of the structure of blood cells (according to B. Alberts et al.)

Erythrocytes (Greek erythros - red)

Table 24. Human blood groups

Lymphocytes

Monocytes

platelets,

Stop bleeding.

The structure of loose fibrous connective tissue:

Loose fibrous connective tissue

Fibroblasts (Greek fibra - fiber, blastos - germ)

Ultramicroscopic diagram of the structure of the ribroblast and the formation of the intercellular substance:

Elastic fibers

Macrophage (macrophage).

Plasma cells or plasma cells

Mast cells or tissue basophils

Reticular cells

Fat cells or adipocytes

pigment cells,

Dense fibrous connective tissue

Dense fibrous connective tissue

Fabrics with special properties

Adipose tissue

The structure of hyaline cartilage covered with perichondrium:

Osteoblasts -

Bone cells:

Osteocytes

Lamellar bone

Scheme of the structure of the tubular bone:

The structure of the osteon in the context:

Rice. 122. The location of the bone crossbars in the cancellous bone .............. 196 Spongy bone

MUSCLE

Rice. 123. Striated (striated) skeletal muscle tissue: .............. 197 124.

Volumetric diagram of the structure of two myofibrils of a striated muscle fiber:

Rice. 125. Scheme of the structure of the sarcomere

G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 9 Fig. 126.

Scheme of the structure of a cardiomyocyte:

NERVE TISSUE

Diagram of the ultramicroscopic structure of a nerve cell:

Rice. 128. Action potential

Diagram of the structure of the synapse:

Synaptic transmission scheme:

Diagram of the structure of nerve fibers:

myelinated nerve fibers

BODIES, SYSTEMS AND APPARATUS OF BODIES

Questions for self-control and repetition

FEATURES OF DEVELOPMENT, GROWTH AND STRUCTURE OF A HUMAN ....... 207 Embryo (embryo)

Cleavage of the zygote and formation of germ layers:

The position of the embryo and germinal membranes in the early stages of human development:

The body of the embryo in cross section:

Features of the structure, growth and development of man

Table 25. Periods of human life

Table 26. Some anthropometric indicators of a newborn and an adult

Table 27. Length, body weight and body surface area in different age periods of postnatal ontogenesis

Change in the proportion of body parts in the process of growth:

Table 28. Surface area of ​​the whole body, head, trunk and limbs, depending on age

Table 29

Table 30. Some gender differences

Table 31. Characteristics of body proportions

Questions for self-control and repetition

musculoskeletal system

PASSIVE PART OF THE LOCOMOTOR APPARATUS

Human skeleton (front view):

Different types of bones:

Table 32

spongy bones

SKELETON AND ITS COMPOUNDS

Bone connections.

Continuous joints of bones and semi-joints:

Joint structure:

Rice. 140. Schematic representation of articular surfaces.

Torso skeleton

Vertebral column:

Vertebra:

First cervical vertebra:

Second cervical vertebra:

Rib cage

A brief outline of the development of the trunk bones in phylo- and ontogenesis

Cerebral region of the skull

Rice. 145. Human skull.

Side view:

Rice. 146. Human skull.

Front view:

Skull as a whole.

Age features of the structure of the skull.

External base of the skull:

Inner base of the skull:

Inner base of the skull:

Rice. 149. Skull of a newborn

Inner base of the skull:

Rice. 149. Skull of a newborn

limb skeleton

Upper limb bones

Bones of the girdle of the upper limb

Bones of the free upper limb

Rice. 150. Bones of the upper limb.

Bones of the right hand (palmar surface):

Bones of the lower limb

Bones of the girdle of the lower limb

G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 10 Fig. 152. Bones of the lower limb

Female pelvis:

Bones of the right foot:

Arches of the foot:

Questions for self-control and repetition

ACTIVE PART OF THE LOCOMOTOR APPARATUS

SKELETAL MUSCLES

Muscle as an organ

Scheme of the beginning and attachment of the muscle:

Elements of biomechanics.

Scheme of the action of muscles on bone levers:

Muscles of the head

Back muscles.

Superficial muscles (anterior surface):

Superficial muscles (posterior surface):

Neck muscles

Muscles of the chest.

Abdominal muscles

Diaphragm and muscles of the posterior abdominal wall:

Muscles of the upper limb

Rice. 161. Muscles of the upper limb.

Muscles of the free upper limb.

Rice. 162. Muscles of the upper limb.

Back view:

Muscles of the lower limb.

Rice. 163. Muscles of the right lower limb.

Rice. 164. Muscles of the right lower limb.

Back view:

Muscles of the free lower limb

Muscle Development

Table 33. Derivatives of visceral arches and their corresponding muscles and nerves

Questions for self-control and repetition

EFFICIENCY, WORK, FATIGUE AND REST .............. 270 Work -

Working capacity -

The main exchange

Mental work is thinking

Scheme of the anatomical (solid line) and physiological (dashed line) muscle diameters of various shapes:

Questions for self-control and repetition

INTERNAL ORGANS

Rice. 166. The structure of the digestive tube

DIGESTIVE SYSTEM

Hunger and appetite.

The structure of the digestive system:

human language

Scheme of the structure of the language:

The tongue is a muscular organ.

Maxillary teeth:

Tooth structure:

Table 34

Diagram of the structure of the pharynx:

Rice. 172. Esophagus and stomach

Stomach (opened its anterior wall):

The structure of the fundic gland of the stomach and its (A, B, C, D) cells:

Small intestine

The structure of the villi of the small intestine:

Duodenum

The liver is the largest human gland

Blood supply to the liver:

The structure of the hepatic beam:

gallbladder

endocrine part,

Colon

ABDOMINAL CAVITY. PERITONE AND PERITONEAL CAVITY

–  –  –

Horizontal (transverse) cut of the body between the bodies of II and III lumbar vertebrae:

Rice. 179. Median (sagittal) section of the trunk (diagram)

A BRIEF OUTLINE OF THE DIGESTIVE SYSTEM DEVELOPMENT IN FIDO- AND ONTOGENESIS.. 297

Questions for self-control and repetition

RESPIRATORY SYSTEM

Respiratory system:

Cartilages, ligaments and joints of the larynx:

Trachea and bronchi:

Branching of the bronchi in the right and left lungs:

The structure of the acinus of the lung:

The structure of the interalveolar septum:

Mediastinum.

FUNCTION OF THE RESPIRATORY SYSTEM

Table 35. Partial pressure and concentration of gases in various media (mm Hg)

Airborne barrier in the lung:

A BRIEF OUTLINE OF THE DEVELOPMENT OF THE RESPIRATORY SYSTEM IN PHYLO- AND ONTOGENESIS

Questions for self-control and repetition

URINARY APPARATUS

URINARY ORGANS

Rice. 187. Right kidney. Frontal (longitudinal) section.

The structure and blood supply of the nephron (scheme):

Human ureters -

Bladder

Woman's urethra

KIDNEY FUNCTION

Table 36. The content of certain substances in plasma and urine

Questions for self-control and repetition

REGENERAL SYSTEM

MALE GENITAL ORGANS

Internal male reproductive organs

Genitourinary apparatus of a man:

Sperm

Diagram of the structure of the testicle and its epididymis:

The structure of the sperm:

vas deferens

Rice. 192. Seminal vesicles. Prostate

The prostate gland (prostate).

Bulbourethral glands (Cooper's) -

spermatic cord

External male genital organs

Scrotum -

Male penis (penis, fallos)

The structure of the penis:

Penile erection mechanism:

Male urethra -

Questions for self-control and repetition

FEMALE GENITAL ORGANS

Internal female reproductive organs

Genitourinary apparatus of a woman:

Rice. 196. The structure of the vesicular follicle of the ovary (Graaffian vesicle): ........... 327 Fallopian tube -

Vagina

External female genital organs

External female genital organs:

BREAST

–  –  –

CROTCH

Questions for self-control and repetition

A BRIEF OUTLINE OF THE DEVELOPMENT OF THE URINARY APPARATUS IN PHYLO- AND ONTOGENESIS

Rice. 198. The scheme of development of the internal male genital organs

Scheme of development of internal female genital organs:

Rice. 200. Scheme of the development of male (I) and female (II) external genital organs: 335 Table 37. Sources of development of male and female genital organs......... 336 GAMETOGENESIS

Gametogenesis

SPERMATOGENESIS

Scheme of spermatogenesis:

spermatid

primary follicle

Rice. 202. Stages of human oocyte development.

Different stages of spermato- and oogenesis:

Questions for self-control and repetition

THE CARDIOVASCULAR SYSTEM

CIRCULATORY SYSTEM

Scheme of the structure of the wall of an artery (A) and a vein (B) of a muscular type of medium caliber:

Rice. 205. Microcirculation

Postcapillary venules

The structure of capillaries of three types:

Opened human heart:

The layout of the pacemaker (pacemaker) and the conduction system of the heart:

Functions of the heart

Automatism (Greek automatos - self-acting, spontaneous) of the heart. 351 Fig. 209. Normal human ECG obtained by bipolar lead from the surface of the body in the direction of the long axis of the heart (according to G. Anthony)

Questions for self-control and repetition

BLOOD SUPPLY OF THE HUMAN BODY

Diagram of the circulatory system:

Human circulatory system (general scheme):

Rice. 212. Arteries of the forearm and hand (view from the palmar side) -

FUNCTION OF THE VASCULAR SYSTEM

A BRIEF OUTLINE OF THE DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM IN FIDO-I

ONTOGENESIS

Fetal circulation:

LYMPHATIC SYSTEM

Questions for self-control and repetition

BODIES OF HEMATOPOISIS AND THE IMMUNE SYSTEM

Immunity (lat. immunitas - liberation from something)

The layout of the central and peripheral organs of the immune system in humans:

BONE MARROW

LYMPHOID TISSUE OF THE WALLS OF THE DIGESTIVE AND RESPIRATORY ORGANS

SYSTEMS

Tonsils -

THE LYMPH NODES

SPLEEN

NON-SPECIFIC RESISTANCE OF THE ORGANISM ........... 374 Questions for self-control and repetition

NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM (CNS)

SPINAL CORD

Topography of segments of the spinal cord:

Spinal cord (transverse section) and reflex arc:

BRAIN

Forebrain. telencephalon,

Rice. 217. Brain. Upper lateral surface of the hemisphere: .................. 378 G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 13 Fig. 218. Brain.

Medial surface of the hemisphere:

Rice. 219. Base of the brain and exit points of cranial nerve roots:

Cortical centers of analyzers:

Core motor analyzer

The core of the visual analyzer

Rice. 221. Cortical center of general sensitivity

Rice. 222. Motor area of ​​the cortex

mastoid bodies,

Cerebellum

Medulla

Rice. 223. Scheme of the structure, location (A) and connections (B) of the limbic system: 385 Reticular formation (Latin rete - network)

A BRIEF OUTLINE OF THE DEVELOPMENT OF THE NERVOUS SYSTEM IN FIDO- AND ONTOGENESIS ......... 386 Fig. 224. Early stages of development of the human nervous system

Table 38. Transformation of the layers of the neural tube and ganglionic plate in human embryogenesis

Human embryonic brain (8th week of development):

Table 39

cranial nerves

The structure of the spinal nerve:

Location and function of the 12 pairs of cranial nerves:

Spinal nerves.

Spinal nerves:

VEGETATIVE (AUTONOMOUS) NERVOUS SYSTEM (ANS)

Rice. 229. Autonomic (autonomic) nervous system

Sympathetic nervous system

Table 40. Influence of sympathetic and parasympathetic nerves on various organs

Questions for self-control and repetition

SENSORS

Table 41. Main categories in the field of sensory processes - modality and quality

ORIGIN OF VISION

choroid

Human eye (section of the eyeball in a horizontal plane, semi-schematically):

Diagram of the structure of the retina:

Rice. 232. Rod-shaped (I) and cone-shaped (II)

Table 42

lacrimal apparatus

Lacrimal apparatus of the right eye:

A BRIEF OUTLINE OF THE DEVELOPMENT OF THE ORGAN OF VISION IN PHYLO- AND ONTOGENESIS

PREDOOR-COCHOLAR ORGANS (ORGAN OF HEARING AND BALANCE)

Organ of hearing:

outer ear

External auditory canal

Middle ear

inner ear,

Balance organ:

Spot epithelium

snail maze

Rice. 236. Propagation of a sound wave

A BRIEF OUTLINE OF THE DEVELOPMENT OF THE ORGANS OF HEARING AND BALANCE IN FIDO- AND ONTOGENESIS.. 412

OLFACTORY ORGAN

Olfactory organ:

organ of taste

Scheme of the structure of the organ of taste:

Diagram of the schematic structure of human skin:

Dermis or skin itself

Sebaceous glands

Touch (mechanoreception)

Questions for self-control and repetition

ENDOCRINE APPARATUS

Tropical (Greek tropos - direction)

G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 14 Fig. 240.

Endocrine glands:

Rice. 241. Scheme of mutual influences of the organs of the hypothalamic-pituitary system: ..... 419 Table 43. Endocrine glands and their hormones

Table 43 continued

End of table 43

THYROID

ADRENAL

PARATHYROID GLANDS

PANCREATIC ISLANDS

PINEAL BODY

DIFFUSE NEUROENDOCRINE SYSTEM (APUD-SYSTEM)

HOMEOSTASIS

Homeostasis (Greek homoios - the same, similar, stasis - stability, balance)

Questions for self-control and repetition

GENETICS

Chromosome shapes:

Chromosomes of different types of plants and animals, shown on the same scale:

Table 44. Some dominant and recessive traits in humans .............. 432

METHODS OF HUMAN GENETICS

Genealogical method (pedigree method). Was

Rice. 244. Genetic symbolism for drawing up the scheme of a genealogy .................. 434 Twin method.

Possible nature of the relationship of identical twins in one blastoderm vesicle:

Table 45

cytogenetic method.

population method

Idiogram of a human karyotype obtained using the differential staining method:

Rice. 247. Micrographs of nerve cells from the anterior horn of the spinal cord of a cat

Rice. 248. Micrograph of a blood smear from a woman; x 1750

ontogenetic method.

Shape of different types of red blood cells in humans:

Modeling method

HEREDITY

INTERACTION OF ALLELIC GENES

Inheritance under complete dominance

monohybrid cross

Rice. 250. Splitting in monohybrid crossing with incomplete dominance in the night beauty (Mirabilis jalapa)

Rice. 251. G. I. Mendel (1822-1884)

Rice. 252. Seven signs of pea Pisum sativum, the inheritance of which was studied by Mendel.

Rice. 253. Generation F1 in two crosses of Mendel.

Second generation hybrids (F2) from crossing peas with smooth and wrinkled seeds:

Table 46. The results of Mendel's experiments on crossing pea plants that differ in one of seven characteristics

Dihybrid and polyhybrid crosses

Rice. 255. Analyzing cross

Rice. 256. Determination of splitting by genotype

Scheme illustrating the behavior of homologous chromosomes during dihybrid crossing:

INTERACTION OF NON-ALLELIC GENES

complementarity

Rice. 258. Inheritance of flower color in Lathyrus odoratus during the interaction of two pairs of genes (complementarity)

Rice. 259. Inheritance of the shape of the crest in chickens during the interaction of two genes....... 454 Epistasis

Rice. 260. Inheritance of coloration in chickens during the interaction of two pairs of genes (epistase):

–  –  –

Table 47. The ratio of phenotypic classes of dihybrid cleavage in F2 for different types of gene interaction

Polymerism

Rice. 261. Distribution by height of adults

Table 48. Inheritance of height in humans

Rice. 262. Dependence of the intensity of skin pigmentation in humans on the number of dominant alleles in the system of polygenes (P) in the genotype

Inheritance of the pod shape in Capsella bursa pastoris through the interaction of two pairs of genes (polymery):

CHROMOSOMAL THEORY OF HEREDITY

LINKED INHERITANCE AND CROSSINGOVER

Rice. 264. T.H. Morgan (1866 - 1945)

Rice. 265. Drosophila fruit fly (Drosophila melanogaster) and its development cycle:

The appearance of parental and recombinant combinations of genes (and traits) when crossing fruit flies that differ in body color and wing development:

sex-linked inheritance

Rice. 267. Splitting by phenotype in reciprocal crossings of while (w) flies with white eyes and normal flies with dark red eyes (w+).

Inheritance of sex-limited and sex-dependent traits

Rice. 268. Sex-linked inheritance in Drosophila when white-eyed females are crossed with red-eyed males (I) and red-eyed females with white-eyed males (II)

Sex determination

Gender detection software

syngamic sex determination,

Annual cycle of Anuraea cochlearis:

Rice. 270. Four types of sex determination (according to F. Ayala)

Rice. 271. The most probable location in the homologous region of the X- and Y chromosomes of those genes that are not completely sex-linked.

Female and male marine worm Bonellia viridis:

Schematic representation of X- (left) and Y- (right) chromosomes in melandrium (Melandrium alba):

Three alleles of one locus are responsible for sex determination in the plant Ecballium elaterium from the gourd family:

Questions for self-control and repetition

VARIABILITY

NON-HEREDITARY (PHENOTYPICAL OR MODIFICATIONAL) VARIABILITY

reaction rate.

Rice. 275. Distribution curve of trait modifications in the variational series:... 478 Pic. 276.

Map of temperature thresholds for wool pigmentation in the Himalayan rabbit:

Arrowhead plant producing three types of leaves:

Rice. 278. Penetrance and expressivity of the Lobe gene in D. melanogaster...................... 480 Types of modifications

Rice. 279. Adaptive modifications in dandelion (Taraxacum officinale): 481 Significance of modifications

Questions for self-control and repetition

HEREDITARY (GENOTYPICAL) VARIABILITY

Combination variability

Rice. 280. Experience of F. Jacob and E. Wolman on termination of conjugation: 484 Mutational variability

Mutation classification

Gene (point) mutations, or transgenerations

Table 49. The frequency of spontaneous mutation of some genes in various organisms

Rice. 281. Types of point mutations: A - transitions; B - transversions

Mechanism of mutagenic action of 5-bromouracil:

Rice. 283. Mechanism of mutagenic action of 2-aminopurine

Table 50. Illustration of the meaning of the terms "base change" and "frame shift"

Chromosomal mutations (rearrangements, or aberrations)

Intrachromosomal rearrangements

Rice. 284. Various types of intrachromosomal rearrangements

Types of missing chromosomes:

–  –  –

Rice. 286. A loop formed in case of heterozygosity for deletions in the chromosomes of the salivary glands of Drosophila.

Rice. 287. Main types of duplications

Rice. 288. Phenotypic manifestations of the same site (16A) in the Drosophila X chromosome - change in the trait Bar

Rice. 289. A possible mechanism for the formation of Lepore hemoglobins as a result of unequal crossing over

Interchromosomal rearrangements

The nature of chromosome conjugation in heterozygosity:

Rice. 291. Chromosome conjugation and consequences of single (I)

Rice. 292. Chromosome conjugation and consequences of single (I) and double (II) crossing over in case of heterozygosity for pericentric inversion

Rice. 293. Various types of translocations (according to F. Ayala et al., with modifications)... 498 Fig. 294. Meiosis in a heterozygote for reciprocal translocation.

Genomic mutations

NON-MULTIPLE CHANGES IN CHROMOSOME NUMBER

Rice. 295. Mosaicism XY/XXY as a consequence of nondisjunction of chromosomes in mitosis (according to F. Ayapa et al.)

MULTIPLE CHANGES IN CHROMOSOME SETS

Rice. 296. Mosaicism of the female body by the presence or absence of normal sweat glands in the skin, due to the expression of normal or mutant alleles of the X-chromosome gene.

polyploidy

Rice. 297. Scheme of mitotic, zygotic and meiotic polyploidization: 503 Pic. 298. Diploid (A), triploid (B) and tetraploid (C) forms of strawberry Fragaria vesca L

Rice. 299. Larger sheaves in tetraploid (right) rye compared to diploid (left)

Polyploidy in rye:

Rice. 301. Fruits and chromosome sets of Raphanus and Brassica and their hybrids:........ 508 CHROMOSOMAL DISEASES IN HUMANS

Rice. 302. Trisomy 21 syndrome (Down's syndrome).

Rice. 303. Karyotypes of a patient with Down syndrome (I), with translocation Down syndrome (II)

Table 51. Dependence of the frequency of birth of children with Down syndrome on the age of the mother * (according to N.D. Tarasenko and G.I. Lushanova)

Rice. 304. Trisomy syndrome 13 (Patau syndrome)

Rice. 306. Karyotype of a patient with trisomy 18 (Edwards syndrome)

Chromosome 5p Syndrome (Crying Cat Syndrome):

SEX CHROMOSOMAL DISTURBANCES

Rice. 308. Klinefelter's syndrome: the appearance of the patient (characterized by high growth, disproportionately long limbs)

Rice. 309. Klinefelter syndrome karyotype

Table 52. Diseases associated with a violation of the number of sex chromosomes in humans

Rice. 310. Karyotype of a patient with X0 monosomy syndrome (Shereshevsky Turner syndrome)

Rice. 311. Monosemia X0 in an 18-year-old girl

Testicular feminization (Morris syndrome):

Mutagenesis

induced mutations

Table 53. External factors that change the effect of X-rays on the occurrence of mutations

The meaning of mutations

Questions for self-control and repetition

Additional drawings

Table 4 (big)

–  –  –

Introduction School and university programs in biology and, accordingly, textbooks lag behind the rapidly developing science. However, the requirements for applicants and students are steadily growing, and a young man, especially an inquisitive and talented one, needs additional literature that would correspond to the current state of the discipline. So far, there is no such literature. The authors tried to fill this gap and create a book that will be in demand in the 21st century. To what extent this has been achieved, we leave it to the reader to judge.

Biology is a set of sciences about wildlife, about the structure, functions, origin, development, diversity and distribution of organisms and communities, their relationships and connections with the external environment. Being unified, biology includes two sections: morphology and physiology. Morphology studies the form and structure of living beings; physiology - the vital activity of organisms, the processes occurring in their structural elements, the regulation of functions. Morphology includes normal anatomy proper (the science of the macroscopic structure of organisms, their organs, apparatuses and systems), histology (the science of the microscopic structure of tissues and organs) and cytology (the science that studies the structure, chemical composition, development and functions of cells, the processes of their reproduction, recovery, adaptation to constantly changing environmental conditions), embryology (the science of the development of organisms). An important branch of biology is genetics, the science of heredity and variability of organisms.

The concept of the three-volume book “Biology. Full course "- the study of the biological structure at various hierarchical levels in close connection with the function performed. Illustrative material (more than a thousand original drawings, diagrams and tables), which facilitates the assimilation of the material, was selected based on these considerations.

–  –  –

CELL

In the process of studying a person, his structures are divided into cells, tissues, morphofunctional units of organs, organs, systems and apparatuses of organs that form the body (Table 1). However, the reader should be cautioned against taking this division literally. The organism is one, it can exist as such only thanks to its integrity. The body is integral, but organized, like many complex systems, according to a hierarchical principle.

It is these structures that form its constituent elements.

–  –  –

The study of each of the levels of organization of the living requires its own approaches and methods.

The first level of organization of living things - cells - studies the branch of biological sciences called cytology.

CELL THEORY

The development of cytology is associated with the creation and improvement of optical devices that allow one to examine and study cells. In 1609 - 1610. Galileo Galilei designed the first microscope, but only in 1624 did he improve it so that it could be used. This microscope magnified 35 - 40 times. A year later, I. Faber gave the device the name “microscope”.

In 1665, Robert Hooke first saw cells in a cork, which he gave the name “cell” to. In the 70s. 17th century Marcello Malpighi described the microscopic structure of some plant organs.

Thanks to the improvement of the microscope by Anton van Leeuwenhoek, it became possible to study cells and the detailed structure of organs and tissues. In 1696, his book "The Secrets of Nature, discovered with the help of the most perfect microscopes" was published. Leeuwenhoek was the first to examine and describe erythrocytes, spermatozoa, discovered the hitherto unknown and mysterious world of microorganisms, which he called ciliates. Leeuwenhoek is rightfully considered the founder of scientific microscopy.

In 1715 H.G. Gertel was the first to use a mirror to illuminate G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 19 microscopic objects, but only a century and a half later E. Abbe created a system of illuminating lenses for a microscope. In 1781, F. Fontana was the first to see and draw animal cells with their nuclei. In the first half of the XIX century. Jan Purkinje perfected the microscopic technique, which allowed him to describe the cell nucleus ("germinal vesicle") and cells in various animal organs. Jan Purkinje was the first to use the term "protoplasm".

R. Brown described the nucleus as a permanent structure and proposed the term "nucleus" nucleus.

In 1838, M. Schleiden created the theory of cytogenesis (cell formation). His main merit is to raise the question of the origin of cells in the body. Based on the work of Schleiden, Theodor Schwann created the cell theory. In 1839, his immortal book "Microscopic investigations on the conformity in the structure and growth of animals and plants" was published.

The main starting points of the cell theory were the following:

All tissues are made up of cells;

Cells of plants and animals have common structural principles, since they arise in the same ways;

Each individual cell is independent, and the activity of the organism is the sum of the vital activity of individual cells.

Rudolf Virchow had a great influence on the further development of cell theory.

He not only brought together all the numerous disparate facts, but also convincingly showed that cells are a permanent structure and arise only by multiplying their own kind - "each cell from a cell" ("omnia cellula e cellulae").

In the second half of the XIX century. the concept of the cell as an elementary organism arose (E. Brücke, 1861). In 1874, J. Carnoy introduced the concept of "cell biology", thereby laying the foundation for cytology as a science of the structure, function and origin of cells.

In 1879 - 1882. W. Flemming described mitosis, in 1883 W. Waldeyer introduced the concept of "chromosomes", a year later O. Hertwig and E. Strasburger simultaneously and independently of each other hypothesized that hereditary traits are contained in the nucleus.

End of the 19th century was marked by the discovery of phagocytosis by Ilya Mechnikov (1892).

At the beginning of the twentieth century. R. Garrison and A. Carrel developed methods for culturing cells in a test tube like unicellular organisms.

In 1928 - 1931. E. Ruska, M. Knoll and B. Borrie designed an electron microscope, thanks to which the true structure of the cell was described and many previously unknown structures were discovered. A. Claude in 1929 - 1949 first used the electron microscope to study cells and developed methods for cell fractionation using ultracentrifugation. All this allowed us to see the cell in a new way and interpret the collected information.

The cell is the elementary unit of all living things, because it has all the properties of living organisms: a highly ordered structure, receiving energy from outside and using it to perform work and maintain order (overcoming entropy), metabolism, active response to stimuli, growth, development, reproduction, doubling and transfer of biological information to descendants, regeneration, adaptation to the environment.

Cell theory in modern interpretation includes the following main provisions:

The cell is the universal elementary unit of the living;

The cells of all organisms are fundamentally similar in structure, function, and chemical composition;

Cells reproduce only by dividing the original cell;

Cells store, process and realize genetic information;

Multicellular organisms are complex cellular ensembles that form integral systems;

It is thanks to the activity of cells in complex organisms that

–  –  –

growth, development, metabolism and energy.

In the twentieth century for discoveries in the field of cytology and related sciences were awarded

Nobel Prizes. Among the laureates were:

1906 Camillo Golgi and Santiago Ramón y Cajal for their discoveries on the structure of neurons;

1908 Ilya Mechnikov and Paul Erlich for their discoveries of phagocytosis (Mechnikov) and antibodies (Ehrlich);

1930 Karl Landsteiner for the discovery of blood types;

1931 Otto Warburg for the discovery of the nature and mechanisms of action of the respiratory enzymes of cytochrome oxidases;

1946 Hermann Möller for the discovery of mutations;

1953 Hans Krebs for the discovery of the citric acid cycle;

1959 Arthur Kernberg and Severe Ochoa for discovering the mechanisms of DNA and RNA synthesis;

1962 Francis Crick, Maurice Wilkinson and James Watson for their discovery of the molecular structure of nucleic acids and their importance in information transmission in living systems;

1963 François Jacob, André Lvov and Jacques Monod for discovering the mechanism of protein synthesis;

1968 Har Gobind Korana, Marshall Nirenberg and Robert Holley for deciphering the genetic code and its role in protein synthesis;

1970 Julius Axelrod, Bernard Katz and Ulf von Euler for their discovery of humoral nerve mediators and their storage, release and inactivation mechanism;

1971 Earl Sutherland for the discovery of the cAMP second messenger (cAMP) and its role in the mechanism of action of hormones;

1974 Christian de Duve, Albert Claude and Georges Palade for discoveries concerning the structural and functional organization of the cell (ultrastructure and function of lysosomes, Golgi complex, endoplasmic reticulum).

PROKARYOTIC AND EUKARYOTIC CELLS

A distinction is made between prokaryotic and eukaryotic organisms. The former include blue-green algae, actinomycetes, bacteria, spirochetes, mycoplasmas, rickettsia and chlamydia, the latter include most algae, fungi and lichens, plants and animals. Unlike a prokaryotic cell, a eukaryotic cell has a nucleus bounded by a sheath of two membranes and a large number of membrane organelles. More detailed differences are presented in Table. 2.

CHEMICAL ORGANIZATION OF THE CELL

Of all the elements of the periodic system, D.I. Mendeleev, 86 constantly present in the human body were found, of which 25 are necessary for normal life, 18 of which are absolutely necessary, and 7 are useful. Professor D.R.

Williams called them the elements of life.

The composition of the substances involved in the reactions associated with the vital activity of the cell includes almost all known chemical elements, and four of them account for about 98% of the mass of the cell. These are oxygen (65 - 75%), carbon (15 - 18%), hydrogen (8 - 10%) and nitrogen (1.5 - 3.0%). The remaining elements are divided into two groups: macroelements (about 1.9%) and microelements (about 0.1%). Macroelements include sulfur, phosphorus, chlorine, potassium, sodium, magnesium, calcium and iron, microelements - zinc, copper, iodine, fluorine, manganese, selenium, cobalt, molybdenum, strontium, nickel, chromium, vanadium, etc. Despite very low content, trace elements play an important role. They affect metabolism. Without them, the normal functioning of each cell individually and the organism as a whole is impossible.

The cell is made up of inorganic and organic substances. Among inorganic

–  –  –

hydrophilic. Hydrophobic substances (fats and fat-like) do not dissolve in water.

There are organic substances with elongated molecules, in which one end is hydrophilic, while the other is hydrophobic; they are called amphipathic. Phospholipids involved in the formation of biological membranes can serve as an example of amphipathic substances.

Inorganic substances (salts, acids, bases, positive and negative ions) make up from 1.0 to 1.5% of the cell mass. Among organic substances, proteins (10 - 20%), fats, or lipids (1 - 5%), carbohydrates (0.2 - 2.0%), nucleic acids (1 - 2%) predominate. The content of low-molecular substances in the cell does not exceed 0.5%.

A protein molecule is a polymer that consists of a large number of repeating units (monomers). Protein monomers - amino acids (there are 20 of them) simultaneously have two active atomic groups - an amino group (it gives the amino acid molecule the properties of a base) and a carboxyl group (it tells the molecule the properties of an acid) (Fig. 1). Amino acids are interconnected by peptide bonds, forming a polypeptide chain (the primary structure of a protein) (Fig. 2).

It twists into a spiral, which, in turn, represents the secondary structure of the protein. Due to a certain spatial orientation of the polypeptide chain, a tertiary structure of the protein arises, which determines the specificity

–  –  –

Rice. 2. A fragment of a polypeptide (according to N. A. Tyukavkina and Yu. I. Baukov, with changes) and the biological activity of a protein molecule. Several tertiary structures combine to form a quaternary structure.

Proteins perform essential functions. Enzymes - biological catalysts that increase the rate of chemical reactions in the cell hundreds of thousands - millions of times, are proteins. Proteins, being part of all cellular structures, perform a plastic (building) function. They form the cellular skeleton. Cell movements are also carried out by special proteins (actin, myosin, dynein). Proteins provide transport of substances into the cell, out of the cell and within the cell. Antibodies, which, along with regulatory functions, also perform protective functions, are also proteins. And finally, proteins are one of the sources of energy.

Carbohydrates are divided into monosaccharides and polysaccharides. Polysaccharides, like proteins, are built from monomers - monosaccharides. Among the monosaccharides in the cell, the most important are glucose (containing six carbon atoms) and pentose (five carbon atoms). Pentoses are part of nucleic acids. Monosaccharides dissolve well in water, polysaccharides - poorly. In animal cells, polysaccharides are represented by glycogen, in plant cells - mainly by soluble starch and

–  –  –

insoluble cellulose, hemicellulose, pectin, etc. Carbohydrates are a source of energy. Complex carbohydrates combined with proteins (glycoproteins) and/or fats (glycolipids) are involved in the formation of cell surfaces and cell interactions.

Lipids include fats and fat-like substances. Fat molecules are built from glycerol and fatty acids (Fig. 3). Fat-like substances include cholesterol, some hormones, and lecithin. Lipids, which are the main component of cell membranes (they are described below), thereby perform a building function.

They are the most important source of energy. So, if with complete oxidation of 1 g of protein or carbohydrates 17.6 kJ of energy is released, then with complete oxidation of 1 g of fat

Nucleic acids are polymeric molecules formed by monomers - nucleotides, each of which consists of a purine or pyrimidine base, a pentose sugar and a phosphoric acid residue. In all cells, there are two types of nucleic acids: deoxyribonucleic (DNA) and ribonucleic (RNA), which differ in the composition of bases and sugars (Table 3, Fig. 4).

The RNA molecule is formed by one polynucleotide chain (Fig. 5).

The DNA molecule consists of two multidirectional polynucleotide chains twisted one around the other in the form of a double helix. Each nucleotide consists of a nitrogenous base, a sugar, and a phosphoric acid residue. In this case, the bases are located

–  –  –

Rice. 4. Structure of nucleic acid molecules:

I - RNA; II - numbering of carbon atoms in the pentose cycle; III-DNA.

An asterisk (*) indicates differences in the structure of DNA and RNA.

Valence bonds are shown in a simplified way: A - adenine; T - thymine; C - cytosine; G

Guanine; U - uracil

–  –  –

Rice. 5. Spatial structure of nucleic acids:

I - RNA; II-DNA; ribbons - sugar-phosphate backbones;

A, C, G, T, U are nitrogenous bases, the lattices between them are hydrogen bonds (according to B. Alberts and advice, with changes) inside the double helix, and the sugar-phosphate skeleton is outside. The nitrogenous bases of both chains are interconnected by complementary hydrogen bonds, while adenine is connected only to thymine, and cytosine to guanine. Depending on the number of the atom in relation to the bond with the base, the ends of the chain are designated as 5 "and 3" (see Fig.

rice. 4 and 5).

DNA carries the genetic information encoded by the sequence of nitrogenous bases. It determines the specificity of the proteins synthesized by the cell, i.e.

the sequence of amino acids in a polypeptide chain. Together with DNA, genetic information is transmitted to daughter cells, which determines (in interaction with environmental conditions) all the properties of the cell. DNA is found in the nucleus and mitochondria, and in

–  –  –

plants and chloroplasts.

All biochemical reactions in the cell are strictly structured and are carried out with the participation of highly specific biocatalysts - enzymes, or enzymes (Greek en - in, zyme - fermentation, leaven), proteins, which, when combined with biological molecules - substrates, reduce the activation energy required for the implementation of a particular reaction (the activation energy is the minimum amount of energy required for a molecule to enter into a chemical reaction).

Enzymes speed up the reaction by 10 orders of magnitude (1010 times).

The names of all enzymes are composed of two parts. The first contains an indication either of the substrate, or of the action, or of both. The second part is the ending, it is always represented by the letters "aza". So, the name of the enzyme "succinate dehydrogenase"

means that it acts on the compounds of succinic acid ("succinate-"), taking away hydrogen from them ("-dehydrogen-").

According to the general type of action, enzymes are divided into 6 classes. Oxireductases catalyze redox reactions, transferases are involved in the transfer of functional groups, hydrolases provide hydrolysis reactions, lyases add groups to double bonds, isomerases transfer compounds to another isomeric form, and ligases (not to be confused with lyases!) bind molecular groups in the chain.

The basis of any enzyme is protein. At the same time, there are enzymes that do not have catalytic activity until a simpler non-protein group, the coenzyme, is added to the protein base (apoenzyme). Sometimes coenzymes have their own names, sometimes they are denoted by letters. Often, the composition of coenzymes includes substances now called vitamins. Many vitamins are not synthesized in the body and therefore must be obtained from food. With their deficiency, diseases (avitaminosis) occur, the symptoms of which, in fact, are manifestations of insufficient activity of the corresponding enzymes.

Some coenzymes play a key role in many of the most important biochemical reactions. An example is coenzyme A (CoA), which ensures the transfer of acetic acid groups. The coenzyme nicotinamide adenine dinucleotide (abbreviated as NAD) provides the transfer of hydrogen ions in redox reactions; the same is true of nicotinamide adenine dinucleotide phosphate (NADP), flavin adenine dinucleotide (FAD), and a number of others. By the way, nicotinamide is one of the vitamins.

STRUCTURE OF THE ANIMAL CELL

The cell is the main structural and functional unit of living organisms, which carries out growth, development, metabolism and energy, stores, processes and implements genetic information. A cell is a complex system of biopolymers, separated from the external environment by a plasma membrane (cytolemma, plasmalemma) and consisting of a nucleus and cytoplasm, in which organelles and inclusions are located.

The French scientist, Nobel Prize winner A. Lvov, based on the achievements of modern cytology, wrote: “Considering the living world at the cellular level, we find its unity: the unity of structure - each cell contains a nucleus immersed in the cytoplasm; unity of function - metabolism is basically similar in all cells; unity of composition - the main macromolecules in all living beings consist of the same small molecules. To build a huge variety of living systems, nature uses a limited number of building blocks. However, different cells also have specific structures. This is due to the performance of their special functions.

The size of human cells varies from a few micrometers (for example, small lymphocytes - about 7) to 200 microns (ovum). Recall that one micrometer (µm) = 10-6 m; 1 nanometer G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 26 (nm) = 10-9 m; 1 angstrom (E) = 10-10 m. The shape of the cells is varied. They can be spherical, ovoid, fusiform, flat, cubic, prismatic, polygonal, pyramidal, stellate, scaly, process, amoeboid, etc.

The main functional structures of a cell are its surface complex, cytoplasm and nucleus.

The surface complex includes the glycocalyx, the plasma membrane (plasmalemma) and the cortical layer of the cytoplasm. It is easy to see that there is no sharp delimitation of the surface complex from the cytoplasm.

In the cytoplasm, hyaloplasm (matrix, cytosol), organelles and inclusions are isolated.

The main structural components of the nucleus are the karyolemma (karyotheca), nucleoplasm and chromosomes; loops of some chromosomes can intertwine, and in this area a nucleolus is formed. Chromatin is often referred to as the structural elements of the nucleus.

However, by definition, chromatin is the substance of chromosomes.

The plasmalemma, karyolemma and part of the organelles are formed by biological membranes.

The main structures that form the cell are listed in Table. 4 and are presented in fig. 6.

BIOLOGICAL MEMBRANES

The structure of biological membranes is most fully reflected by the fluid-mosaic model, the original version of which was proposed in 1972 by G. Nicholson and S.

Singer. The membrane consists of two layers of amphipathic lipid molecules (bilipid layer, or bilayer). Each such molecule has two parts - a head and a tail. The tails are hydrophobic and face each other. Heads, on the other hand, are hydrophilic

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Rice. 6. The main structures of an animal cell: 1 - agranular (smooth) endoplasmic reticulum; 2 - glycocalyx;

3 - plasmalemma; 4 - cortical junction of the cytoplasm 2+3+4 = cell surface complex; 5 - pinocytic vesicles; 6 - mitochondrion;

7 - intermediate filaments; 8 - secretory granules; 9 - allocation of a secret; 10- Golgi complex; 11 - transport bubbles; 12 - lysosomes;

13 - phagosome; 14 - free ribosomes; 15 - polyribosome; 16 - granular endoplasmic reticulum; 17 - bordered vesicle; 18 - nucleolus; 19 nuclear lamina; 20 - perinuclear space, limited by the outer and inner membranes of the karyotheca; 21 - chromatin; 22 - pore complex; 23 cell center; 24 - microtubule; 25 - peroxisome

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and directed outward and inward of the cell. Protein molecules are immersed in the bilipid layer (Fig. 7).

On fig. 8 is a schematic representation of the phosphatidylcholine phospholipid molecule.

One of the fatty acids is saturated, the other is unsaturated. Lipid molecules are capable of rapidly diffusing laterally within one monolayer and very rarely pass from one monolayer to another.

Rice. 8. Phospholipid phosphatidylcholine molecule:

A - polar (hydrophilic) head: 1 - choline, 2 - phosphate, 3 - glycerol; IN

Non-polar (hydrophobic) tail: 4 - saturated fatty acid, 5

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unsaturated fatty acid, CH=CH - cis double bond Bilipid layer behaves like a liquid with a significant surface tension. As a result, it forms closed cavities that do not collapse.

Some proteins pass through the entire thickness of the membrane, so that one end of the molecule faces the space on one side of the membrane, the other on the other. They are called integral (transmembrane). Other proteins are located in such a way that only one end of the molecule faces the near-membrane space, while the other end lies in the inner or outer monolayer of the membrane. Such proteins are called internal or, respectively, external (sometimes both are called semi-integral). Some proteins (usually transported across the membrane and temporarily residing in it) may lie between the phospholipid layers.

The ends of protein molecules facing the near-membrane space can bind to various substances located in this space. Therefore, integral proteins play an important role in the organization of transmembrane processes. Semi-integral proteins are always associated with molecules that carry out reactions to perceive signals from the environment (molecular receptors) or to transmit signals from the membrane to the environment. Many proteins have enzymatic properties.

The bilayer is asymmetric: different lipids are located in each monolayer, glycolipids are found only in the outer monolayer so that their carbohydrate chains are directed outward. Cholesterol molecules in eukaryotic membranes lie in the inner half of the membrane facing the cytoplasm. Cytochromes are located in the outer monolayer, and ATP synthetases are located on the inner side of the membrane.

Like lipids, proteins are also capable of lateral diffusion, but its rate is slower than that of lipid molecules. The transition from one monolayer to another is practically impossible.

Bacteriorhodopsin is a polypeptide chain consisting of 248 amino acid residues and a prosthetic group - a chromophore that absorbs light quanta and is covalently linked to lysine. Under the influence of a light quantum, the chromophore is excited, which leads to conformational changes in the polypeptide chain.

This causes the transfer of two protons from the cytoplasmic surface of the membrane to its outer surface, as a result of which an electrical potential arises in the membrane, causing the synthesis of ATP. Among the membrane proteins of prokaryotes, there are permease-carriers, enzymes that carry out various synthetic G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 30 processes, including ATP synthesis.

The concentration of substances, in particular ions, is not the same on both sides of the membrane.

Therefore, each side carries its own electrical charge. Differences in the concentration of ions create, respectively, the difference in electrical potentials.

Surface complex The surface complex (Fig. 9) ensures the interaction of the cell with its environment.

In this regard, it performs the following main functions:

delimiting (barrier), transport, receptor (perception of signals from the environment external to the cell), as well as the function of transmitting information perceived by receptors to deep structures of the cytoplasm.

The basis of the surface complex is a biological membrane, called the outer cell membrane (in other words, the plasmalemma). Its thickness is about 10 nm, so it is indistinguishable in a light microscope. The structure and role of biological membranes as such was discussed earlier, while the plasmalemma provides, first of all, a delimiting function in relation to the environment external to the cell. Naturally, it also performs other functions: transport and receptor (perception of signals from the external

Rice. 9. Surface complex:

1 - glycoproteins; 2 - peripheral proteins; 3 - hydrophilic heads of phospholipids; 4 - hydrophobic tails of phospholipids; 5 - microfilaments;

6 - microtubules; 7 - submembrane proteins; 8 - transmembrane (integral) protein (according to A. Ham and D. Cormack, with changes) for the cell medium). The plasma membrane thus provides the surface properties of the cell.

The outer and inner electron-dense layers of the plasmalemma are about 2-5 nm thick, the middle electron-transparent layer is about 3 nm. During freezing-cleavage, the membrane is divided into two layers: layer A, containing numerous, sometimes arranged in groups, large particles 8–9.5 nm in size, and layer B, containing approximately the same particles (but in a smaller amount) and small depressions. Layer A is a cleavage of the inner (cytoplasmic) half of the membrane, layer B is the outer.

Protein molecules are immersed in the bilipid layer of the plasmalemma. Some of them (integral, or transmembrane) pass through the entire thickness of the membrane, others (peripheral or external) lie in the inner or outer monolayers of the membrane. Some integral proteins are linked by non-covalent bonds to cytoplasmic proteins. Like lipids, protein molecules are also amphipathic - their hydrophobic regions are surrounded by similar "tails" of lipids, while hydrophilic ones face outside or inside the cell.

G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 31 Proteins carry out most of the membrane functions: many of them are receptors, others are enzymes, and still others are carriers. Like lipids, proteins are also capable of lateral diffusion, but its rate is slower than that of lipid molecules. The transition of protein molecules from one monolayer to another is practically impossible.

Since each monolayer contains its own proteins, the bilayer is asymmetric. Several protein molecules can form a channel through which certain ions or molecules pass.

One of the most important functions of the plasma membrane is transport.

Recall that the "tails" of lipids facing each other form a hydrophobic layer that prevents the penetration of polar water-soluble molecules. As a rule, the inner cytoplasmic surface of the plasma membrane carries a negative charge, which facilitates the penetration of positively charged ions into the cell.

Small (18 Da) uncharged water molecules quickly diffuse through membranes, small polar molecules (for example, urea, CO2, glycerol), hydrophobic molecules (O2, N2, benzene) also quickly diffuse, large uncharged polar molecules are not able to diffuse at all (glucose, sucrose). At the same time, these substances diffuse easily through the cytolemma due to the presence in it of membrane transport proteins specific for each chemical compound.

These proteins can function on the principle of uniport (transfer of one substance across the membrane) or cotransport (transfer of two substances). The latter can be in the form of a symport (transfer of two substances in one direction) or an antiport (transfer of two substances in opposite directions) (Fig. 10).

During transport, the second substance is H +. Uniport and symport are the main ways of transferring most of the substances necessary for its vital activity into the prokaryotic cell.

There are two types of transport: passive and active. The first does not require energy, the second is energy-dependent (Fig. 11). Passive transport of uncharged molecules is carried out along the concentration gradient, transport of charged molecules depends on the H+ concentration gradient and the transmembrane potential difference, which are combined into a transmembrane H+ gradient, or an electrochemical proton gradient (Fig. 12). As a rule, the inner cytoplasmic surface of the membrane carries a negative charge, which facilitates the penetration of positively charged ions into the cell.

Diffusion (lat. diffusio - spreading, spreading) is the transition of ions or molecules caused by their Brownian movement through membranes from the zone,

Rice. 10. Scheme of functioning of transport proteins:

1 - transported molecule; 2 - cotransported molecule;

3 - lipid bilayer; 4 - carrier protein; 5 - antiport; 6 - symport;

7 - cotransport; 8 - uniport (according to B. Alberts et al.) 1 - transported molecule; 2 - channel-forming protein;

3 - carrier protein; 4 - electrochemical gradient; 5 - energy;

6 - active transport; 7 - passive transport (facilitated diffusion); 8 - diffusion mediated by a carrier protein;

9 - diffusion through the channel; 10- simple diffusion; 11 - lipid bilayer (according to B. Alberts et al.)

Rice. 12. Electrochemical proton gradient. Components of the gradient:

1 - inner mitochondrial membrane;

2 - matrix;

3 - proton-motive force due to the membrane potential;

4 - proton motive force due to the concentration gradient of protons (according to B. Alberts et al.) where these substances are in a higher concentration, to a zone with a lower concentration until the concentrations on both sides of the membrane are equalized.

Diffusion can be neutral (uncharged substances pass between lipid molecules or through a channel-forming protein) or facilitated (specific carrier proteins bind the substance and carry it across the membrane). Facilitated diffusion is faster than neutral diffusion. On fig. 13 shows a hypothetical model for the functioning of carrier proteins in facilitated diffusion.

Water enters the cell by osmosis (Greek osmos - push, pressure). At present, the existence of the smallest temporary pores in the cytolemma, which appear as needed, is mathematically proved.

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Active transport is carried out by carrier proteins, while energy is consumed due to the hydrolysis of ATP or proton potential. Active transport occurs against a concentration gradient.

In the transport processes of a prokaryotic cell, the main role is played by the electrochemical proton gradient, while the transfer goes against the concentration gradient of substances. On the cytolemma of eukaryotic cells using a sodium potassium pump

Rice. 13. Scheme of the functioning of carrier proteins:

1 - transported substance; 2 - concentration gradient;

3 - transport protein that facilitates diffusion;

4 - lipid bilayer (according to B. Alberts et al.)

Rice. 14. (Na*K*)ATPase:

I - extracellular space; II - intracellular space (cytoplasm); 1 - concentration gradient of sodium ions; 2 – site of potassium binding; 3 - concentration gradient of potassium ions; 4 – sodium binding site. During hydrolysis inside the cell of each ATP molecule, three Na* ions are pumped out of the cell and two K* ions are pumped into the cell (according to B.

Alberts et al.) the membrane potential is maintained. This pump, which functions as an antiport pumping K+ into the cell against concentration gradients and Na+ into the extracellular medium, is the ATPase enzyme (Fig. 14). At the same time, conformational changes occur in ATPase, as a result of which Na + is transferred through the membrane and excreted into the extracellular environment, and K + is transferred into the cell. The process resembles the facilitated diffusion model depicted in Fig. 13.

ATPase also carries out active transport of amino acids and sugars.

A similar mechanism is present in the cytolemma of aerobic bacteria. However, their enzyme, instead of hydrolyzing ATP, synthesizes it from ADP and phosphate using a proton gradient. The bacteriorhodopsin described above functions in the same way. In other words, the same enzyme carries out both the synthesis and hydrolysis of ATP.

Due to the presence of a total negative charge in the cytoplasm of a prokaryotic cell, a number of

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uncharged molecules are transported according to the principle of symport with H+, the energy source is the transmembrane electrochemical gradient H+ (for example, glycine, galactose, glucose), negatively charged substances are transported according to the principle of symport also with H+ due to the concentration gradient H+, Na+ transport is carried out along the principle of antiport with H+, which is also transferred into the cell due to the concentration gradient of H+; the mechanism is similar to the Na+ K+ eukaryotic pump. Positively charged substances enter the cell according to the uniport principle due to the transmembrane difference in electrical potentials.

The outer surface of the plasmalemma is covered with glycocalyx (Fig. 15). Its thickness is different and fluctuates even in different parts of the surface of one cell from 7.5 to 200 nm. The glycocalyx is a collection of molecules associated with membrane proteins. In composition, these molecules can be chains of polysaccharides, glycolipids, and glycoproteins.

Many of the glycocalyx molecules function as specific molecular receptors. The terminal free section of the receptor has a unique spatial configuration. Therefore, only those molecules that are outside the cell can combine with it.

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which also have a unique configuration, but mirror-symmetric with respect to the receptor. It is due to the existence of specific receptors that the so-called signal molecules, in particular hormone molecules, can be fixed on the cell surface.

The more specific specific receptors are in the glycocalyx, the more actively the cell reacts to the corresponding signal substances. If there are no molecules in the glycocalyx that specifically bind to external substances, the cell does not react to the latter. Thus, the glycocalyx, along with the plasmalemma itself, also provides the barrier function of the surface complex.

Surface structures of the cytoplasm adjoin the deep surface of the plasmalemma. They bind to plasmalemma proteins and carry out the transfer of information to deep structures, triggering complex chains of biochemical reactions.

They, changing their mutual position, change the configuration of the plasmalemma.

Intercellular connections When cells come into contact with each other, their plasma membranes enter into interactions. In this case, special unifying structures are formed - intercellular connections (Fig.

16). They are formed during the formation of a multicellular organism during embryonic development and during the formation of tissues. Intercellular connections are divided into simple and complex. In simple junctions, the plasma membranes of neighboring cells form outgrowths like teeth, so that a tooth of one cell is embedded between two teeth of another (dentate junction) or interlaced interdigitations (finger-shaped junction). Between the plasma membranes of neighboring cells G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 35 there is always an intercellular gap 15 - 20 nm wide.

Rice. 16. Intercellular connections:

I - tight connection; II - desmosome; III - hemidesmosome;

IV - nexus (gap-like connection);

1 - plasma membranes of adjacent cells; 2 - adhesion zones;

3 - electron-dense plates; 4 - intermediate filaments (tonofilaments) fixed in the plate; 5 - intercellular filaments; 6

basement membrane; 7 - underlying connective tissue; 8 - connexons, each of which consists of 6 subunits with a cylindrical channel (according to A. Ham and D. Cormac and according to B. Alberts et al., with changes) Complex compounds, in turn, are divided into adhesive, closing and conductive. Adhesion junctions include the desmosome, hemi-desmosome, and the band of adhesion (ribbon-like desmosome). The desmosome consists of two electron-dense halves belonging to the plasma membranes of neighboring cells, separated by an intercellular space of about 25 nm in size, filled with a fine-fibrillar substance of a glycoprotein nature. Keratin tonofilaments, resembling head hairpins, are attached to the sides of both lamellae of the desmosome facing the cytoplasm. In addition, intercellular fibers connecting both plates pass through the intercellular space.

The hemidesmosome, formed by only one plate with the tonofilaments included in it, attaches the cell to the basement membrane. The clutch belt, or ribbon-like desmosome, is a "ribbon" that goes around the entire surface of the cell near its apical section. The width of the intercellular space filled with fibrous substance does not exceed 15-20 nm. The cytoplasmic surface of the "tape" is compacted and strengthened by the contractile bundle of actin G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 36 filaments.

Tight junctions, or locking zones, pass through the apical surfaces of the cells in the form of belts 0.5–0.6 µm wide. There is practically no intercellular space and glycocalyx in tight contacts between the plasma membranes of neighboring cells. The protein molecules of both membranes are in contact with each other, so the molecules do not pass through tight contacts. On the plasmalemma of one cell there is a network of ridges formed by chains of elliptical protein particles located in the inner monolayer of the membrane, which correspond to grooves and grooves on the plasmalemma of the neighboring cell.

Conductive connections include the nexus, or gap-like junction, and the synapse.

Water-soluble small molecules with a molecular weight of not more than 1500 Da pass through them from one cell to another. Many human (and animal) cells are connected by such contacts. In the nexus, between the plasma membranes of neighboring cells, there is a space 2–4 nm wide. Both plasma membranes are interconnected by connexons - hollow hexagonal protein structures about 9 nm in size, each of which is formed by six protein subunits. The method of freezing and chipping showed that on the inner part of the membrane there are hexagonal particles 8–9 nm in size, and on the outer part there are corresponding pits. Gap junctions play an important role in the function of cells with pronounced electrical activity (for example, cardiomyocytes). Synapses play an important role in the implementation of the functions of the nervous system.

Microvilli Microvilli provide an increase in cell surface. This, as a rule, is associated with the implementation of the function of absorption of substances from the environment external to the cell. Microvilli (Fig. 17) are derivatives of the surface complex of the cell. They are protrusions of the plasmalemma 1-2 µm long and up to 0.1 µm in diameter. In the hyaloplasm, there are longitudinal bundles of actin microfilaments, so the length of the microvilli can change. This is one of the ways to regulate the activity of substances entering the cell. At the base of the microvillus in the surface complex of the cell, its microfilaments combine with elements of the cytoskeleton.

The surface of microvilli is covered with glycocalyx. With a special activity of absorption, the microvilli are so close to each other that their glycocalyx merges. Such a complex is called a brush border. In the brush border, many glycocalyx molecules have enzymatic activity.

Rice. 17. Microvilli and stereocilia:

I and II - microvilli; III and IV - stereocilia; I-III - schemes;

IV - electron micrograph; 1 - glycocalyx; 2 - plasmalemma;

3 - bundles of microfilaments (according to B. Alberts et al., with changes)

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Particularly large microvilli up to 7 microns in length are called stereocilia (see Fig.

17). They are present in some specialized cells (for example, in sensory cells in the organs of balance and hearing). Their role is not related to absorption, but to the fact that they can deviate from their original position. Such a change in the configuration of the cell surface causes its excitation, the latter is perceived by the nerve endings, and the signals enter the central nervous system.

Stereocilia can be considered as special organelles that have evolved through the modification of microvilli.

Biological membranes divide the cell into separate areas that have their own structural and functional features - compartments, and also delimit the cell from its environment. Accordingly, the membranes associated with these compartments have their own characteristic features.

NUCLEUS A well-formed cell nucleus (Fig. 18) is present only in eukaryotes. Prokaryotes also have nuclear structures such as chromosomes, but they are not contained in a separate compartment. In most cells, the shape of the nucleus is spherical or ovoid, but there are nuclei of other shapes (annular, rod-shaped, fusiform, bean-shaped, segmented, etc.). The sizes of the nuclei vary widely - from 3 to 25 microns. The ovum has the largest nucleus. Most human cells have a single nucleus, but there are two nuclei (for example, some neurons, liver cells, cardiomyocytes). Two-, and sometimes multi-nucleus, is associated with polyploidy (Greek polyploos - multiple, eidos - view). Polyploidy is an increase in the number of chromosome sets in the nuclei of cells.

We take this opportunity to note that sometimes structures are called multinucleated cells that were formed not as a result of polyploidization of the original cell, but as a result of the fusion of several mononuclear cells. Such structures have a special name - symplasts; they are found, in particular, in the composition of skeletal striated muscle fibers.

Rice. 18. Cell nucleus:

1 - outer membrane of the karyotheca (outer nuclear membrane);

2 - perinuclear space;

3 - inner membrane of the karyotheca (inner nuclear membrane);

4 - nuclear lamina;

5 - pore complex;

6 - ribosomes;

7 - nukpeoppasma (nuclear juice); 8 - chromatin; 9 - cistern of granular endoplasmic reticulum; 10 - nucleolus (according to B. Alberts et al., with changes)

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In eukaryotes, the chromosomes are concentrated inside the nucleus and separated from the cytoplasm by the nuclear membrane, or karyoteka. The karyotheca is formed by the expansion and fusion of cisterns of the endoplasmic reticulum with each other. Therefore, the karyotheca is formed by two membranes - internal and external. The space between them is called the perinuclear space. It has a width of 20 - 50 nm and maintains communication with the cavities of the endoplasmic reticulum. From the side of the cytoplasm, the outer membrane is often covered with ribosomes.

In places, the inner and outer membranes of the karyotheca merge, and a pore forms at the fusion site. The pore does not gape: between its edges, protein molecules are ordered, so that a pore complex is formed as a whole.

The pore complex (Fig. 19) is a complex structure that consists of two rows

Rice. 19. Pore complex:

A - spatial reconstruction; B - diagram of the main structures;

C - scheme of molecular organization; 1 - peripheral granules;

2 - central granule; 3 - pore diaphragm (according to B. Alberts et al., with changes) of interconnected protein granules, each of which contains 8 granules located at an equal distance from each other on both sides of the nuclear envelope.

These granules are larger than ribosomes. Granules located on the cytoplasmic side of the pore determine the osmiophilic material surrounding the pore. In the center of the opening of the pore, there is sometimes a large central granule associated with the granules described above (possibly, these are particles transported from the nucleus to the cytoplasm). The opening of the pore is closed by a thin diaphragm. Apparently, there are cylindrical channels in the burrow complexes. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 39 with a diameter of about 9 nm and a length of about 15 nm.

Through the pore complexes, selective transport of molecules and particles from the nucleus to the cytoplasm and vice versa is carried out. Pores can occupy up to 25% of the core surface.

The number of pores in one nucleus reaches 3000 - 4000, and their density is about 11 per 1 μm2 of the nuclear envelope. Mostly different types of RNA are transported from the nucleus to the cytoplasm. All enzymes necessary for RNA synthesis come from the cytoplasm to the nucleus to regulate the intensity of these synthesis. In some cells, hormone molecules that also regulate the activity of RNA synthesis come from the cytoplasm to the nucleus.

The inner surface of the karyoteca is associated with numerous intermediate filaments (see the Cytoskeleton section). Together, they form a thin plate here, called the nuclear lamina (Fig. 20 and 21). Chromosomes are attached to it.

The nuclear lamina is associated with pore complexes and plays a major role in maintaining the shape of the nucleus. It is built from intermediate filaments of a special structure.

The nucleoplasm is a colloid (usually in the form of a gel). Various molecules are transported along it, it contains a wide variety of enzymes, and RNA enters it from chromosomes. In living cells, it is outwardly homogeneous.

Rice. 20. Surface structures of the nucleus:

1 - inner nuclear membrane; 2 - integral proteins; 3 - nuclear lamina proteins; 4 - chromatin fibril (part of the chromosome) (according to B. Alberts et al., with changes)

Rice. 21. Nucleus and perinuclear region of the cytoplasm:

1 - granular endoplasmic reticulum; 2 - pore complexes;

3 - inner nuclear membrane; 4 - outer nuclear membrane;

5 - nuclear lamina and submembrane chromatin (according to B. Alberts et al., with changes) In living cells, the nucleoplasm (karyoplasm) is outwardly homogeneous (except for the nucleolus).

After fixation and processing of tissues for light or electron microscopy, two types of chromatin become visible in the karyoplasm (Greek chroma - paint): well-stained electron-dense heterochromatin formed by osmiophilic G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 40 granules 10 - 15 nm in size and fibrillar structures about 5 nm thick, and light euchromatin.

Heterochromatin is located mainly near the inner nuclear membrane, in contact with the nuclear plate and leaving free pores, and around the nucleolus.

Euchromatin is located between clusters of heterochromatin. In fact, chromatin is a complex of substances that form chromosomes - DNA, protein and RNA in a ratio of 1: 1.3: 2. The basis of each chromosome is formed by DNA, the molecule of which has the form of a spiral. It is packed with various proteins, among which there are histone and non-histone proteins. As a result of the association of DNA with proteins, deoxynucleoproteins (DNPs) are formed.

Chromosomes and nucleoli In the chromosome (Fig. 22) the DNA molecule (see Fig. 4 and 5) is packed compactly. Thus, information stored in a sequence of 1 million nucleotides in a linear arrangement would occupy a segment 0.34 mm long. As a result of compaction, it occupies a volume of 10–15 cm3. The length of one human chromosome in an extended form is about 5 cm, the length of all chromosomes is about 170 cm, and their mass is b x 10-12 g.

DNA is associated with histone proteins, resulting in the formation of nucleosomes, which are the structural units of chromatin. Nucleosomes, resembling beads with a diameter of 10 nm, consist of 8 histone molecules (two molecules of histones H2A, H2B, H3 and H4 each), around which a DNA segment is twisted, including

Rice. 22. Levels of DNA packaging in a chromosome:

I - nucleosomal thread: 1 - histone Hi; 2 -DNA: 3 - other histones:

II - chromatin fibril; III - a series of loop domains;

IV - condensed chromatin in the loop domain;

V - metaphase chromosome: 4 - microtubules of the achromatin spindle (kinetochore); 5 - kinetochore; 6 - centromere; 7 - chromatids (according to B. Alberts et al., with changes and additions)

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146 base pairs. Between the nucleosomes there are linker regions of DNA consisting of 60 base pairs, and the H1 histone provides mutual contact between adjacent nucleosomes. Nucleosomes are only the first level of DNA folding.

Chromatin is presented in the form of fibrils about 30 nm thick, which form loops about 0.4 μm long each, containing from 20,000 to 30,000 base pairs, which, in turn, are further compacted, so that the metaphase chromosome has an average size of 5 x 1.4 µm.

As a result of supercoiling, DNPs in the dividing nucleus of chromosomes (Greek chroma paint, soma - body) become visible when magnified with a light microscope.

Each chromosome is made up of one long DNP molecule. They are elongated rod-shaped structures with two arms separated by a centromere. Depending on its location and the relative position of the arms, three types of chromosomes are distinguished: metacentric, having approximately the same arms;

acrocentric, having one very short and one long arm;

submetacentric, which have one long and one shorter arm. Some acrocentric chromosomes have satellites (satellites) - small sections of the short arm connected to it by a thin non-staining fragment (secondary constriction). The chromosome contains eu- and heterochromatic regions. The latter in the non-dividing nucleus (outside mitosis) remain compact. The alternation of eu- and heterochromatic regions is used to identify chromosomes.

The metaphase chromosome consists of two sister chromatids connected by a centromere, each of which contains one DNP molecule, stacked in the form of a supercoil. During spiralization, the sections of eu- and heterochromatin fit in a regular way, so that alternating transverse bands are formed along the length of the chromatids. They are identified using

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special colours. The surface of chromosomes is covered with various molecules, mainly ribonucleoproteins (RNPs). Somatic cells have two copies of each chromosome, they are called homologous. They are the same in length, shape, structure, arrangement of stripes, they carry the same genes that are localized in the same way. Homologous chromosomes can differ in the alleles of the genes they contain. A gene is a section of a DNA molecule on which an active RNA molecule is synthesized (see the "Protein Synthesis" section). The genes that make up human chromosomes can contain up to two million base pairs.

So, chromosomes are double strands of DNA surrounded by a complex system of proteins. Histones are associated with some sections of DNA. They can cover them or release them. In the first case, this region of the chromosome is not capable of synthesizing RNA, while in the second case, synthesis occurs. This is one of the ways to regulate the functional activity of the cell by derepression and repression of genes. There are other ways to do this as well.

Some sections of chromosomes remain surrounded by proteins constantly and in a given cell they never participate in RNA synthesis. They can be called blocked.

Blocking mechanisms are varied. Typically, such areas are very strongly spiralized and covered not only by histones, but also by other proteins with larger molecules.

Despiralized active regions of chromosomes are not visible under a microscope. Only a weak homogeneous basophilia of the nucleoplasm indicates the presence of DNA; they can also be detected by histochemical methods. Such areas are referred to as euchromatin.

Inactive highly helical complexes of DNA and high molecular weight proteins stand out when stained in the form of clumps of heterochromatin. Chromosomes are fixed on the inner surface of the karyotheca to the nuclear lamina.

In general, chromosomes in a functioning cell provide the synthesis of RNA necessary for the subsequent synthesis of proteins. In this case, the reading of genetic information is carried out - its transcription. Not the entire chromosome is directly involved in it.

Different parts of the chromosomes provide the synthesis of different RNA. Particularly distinguished are the sites synthesizing ribosomal RNA (rRNA); not all chromosomes have them. These sites are called nucleolar organizers. The nucleolar organizers form loops. The tops of the loops of different chromosomes gravitate towards each other and meet together. Thus, the structure of the nucleus, called the nucleolus, is formed (Fig. 23). It has three components. The weakly stained component corresponds to chromosome loops, the fibrillar component corresponds to transcribed rRNA, and the globular component corresponds to ribosome precursors.

The nucleoli are also visible under a light microscope. Depending on the functional activity of the cell, either smaller or larger regions of organizers are included in the formation of the nucleolus. Sometimes their grouping can take place not in one, but in several places.

Rice. 23. The structure of the nucleolus:

I - scheme: 1 - caroteca; 2 - nuclear lamina; 3 - nucleolar organizers of chromosomes: 4 - ends of chromosomes associated with the nuclear lamina; II - nucleolus in the nucleus of the cell (electron microscope photograph) (according to B. Alberts et al., with changes)

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In these cases, several nucleoli are found in the cell. The areas in which the nucleolar organizers are active are detected not only at the electron microscopic level, but also by light-optics during special processing of preparations (special methods of silver impregnation).

From the nucleolus, ribosome precursors move to the pore complexes. During the passage of the pores, further formation of ribosomes occurs.

Chromosomes are the leading components of the cell in the regulation of all metabolic processes: any metabolic reactions are possible only with the participation of enzymes, while enzymes are always proteins, proteins are synthesized only with the participation of RNA.

At the same time, chromosomes are also the guardians of the hereditary properties of the organism.

It is the sequence of nucleotides in DNA chains that determines the genetic code.

The totality of all genetic information stored in chromosomes is called the genome. When preparing a cell for division, the genome is doubled, and during the division itself, it is equally distributed between daughter cells. All problems related to the organization of the genome and the patterns of transmission of hereditary information are presented in the course of genetics.

Karyotype The metaphase nucleus can be isolated from the cell, the chromosomes can be moved apart, counted and their shape studied. Cells of individuals of each biological species have the same number of chromosomes. Each chromosome during metaphase has its own structural features. The totality of these features is designated by the concept of "karyotype" (Fig. 24).

Knowledge of the normal karyotype is necessary to identify possible abnormalities.

Such deviations always serve as a source of hereditary diseases.

Rice. 24. Human karyotype (healthy male) (according to B. Alberts et al. and V.P. Mikhailov, with changes) one pair of sex chromosomes (or XX in women, G.L. Bilich. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC Publishing House ONIKS 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 44 or XY for men).

In 1949, M. Barr discovered special dense bodies in the nuclei of cat neurons, which were absent in males. These bodies are also found in the interphase nuclei of other somatic cells of female individuals. They were called sex chromatin bodies (Barr bodies). In humans, they are about 1 µm in diameter and are best identified in neutrophilic segmented leukocytes, where they appear as a "drumstick" associated with the nucleus. They are well distinguishable in the epithelial cells of the buccal mucosa, taken by scraping. Barr bodies are one inactivated condensed X chromosome.

CYTOPLASM

The main structures of the cytoplasm are hyaloplasm (matrix), organelles and inclusions.

Hyaloplasm In physical and chemical terms, hyaloplasm (Greek hyalos - glass) is a colloid consisting of water, ions and many molecules of organic substances. The latter belong to all classes - to carbohydrates, and to lipids, and to proteins, as well as to complex compounds such as glycolipids, glycoproteins and lipoproteins. Many of the proteins have enzymatic activity. A number of important biochemical reactions take place in the hyaloplasm, in particular, glycolysis is carried out - the phylogenetically most ancient process of energy release (Greek glykys - sweet and lysis - decay), as a result of which a six-carbon glucose molecule decomposes into two three-carbon molecules of pyruvic acid with the formation of ATP (see. section "Basic reactions of tissue metabolism").

The molecules of hyaloplasm, of course, interact with each other in a very orderly manner, but the nature of its spatial organization is still not clear enough.

Therefore, we can only speak in general terms that the hyaloplasm is structured at the molecular level.

It is in the hyaloplasm that organelles and inclusions are suspended.

Organelles Organelles are called elements of the cytoplasm, structured at the ultramicroscopic level and performing specific functions of the cell; organelles are involved in the implementation of those functions of the cell that are necessary to maintain its vital activity. This includes ensuring its energy metabolism, synthetic processes, ensuring the transport of substances, etc.

Organelles inherent in all cells are called general-purpose organelles, while those inherent in some specialized types of cells are called special. Depending on whether the structure of the organelle includes a biological membrane or not, membrane and non-membrane organelles are distinguished.

General Purpose Organelles

NON-MEMBRANE ORGANELLES

Non-membrane organelles include the cytoskeleton, cell center, and ribosomes.

CYTOSKELETON

The cytoskeleton (cellular skeleton), in turn, is formed by three components:

microtubules, microfilaments and intermediate filaments.

Microtubules Microtubules (Fig. 25) permeate the entire cytoplasm of the cell. Each of them is a hollow cylinder with a diameter of 20 - 30 nm. The microtubule wall has a thickness of 6-8 nm. It is formed by 13 threads (protofilaments) twisted according to G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 45 spirals one above the other. Each thread, in turn, is made up of tubulin protein dimers. Each dimer is represented by a- and R-tubulin. The synthesis of tubulins occurs on the membranes of the granular endoplasmic reticulum, and the assembly in a spiral occurs in the cell center.

Accordingly, many microtubules have a radial direction with respect to centrioles. From here they spread throughout the cytoplasm. Part of them

Rice. 25. Microtubule structure:

1 - tubulin subunits;

2 - associated proteins;

3 - moving particles are located under the plasmalemma, where they, together with bundles of microfilaments, participate in the formation of the terminal network.

Microtubules are strong and form the supporting structures of the cytoskeleton. Part of the microtubules is located in accordance with the forces of compression and tension experienced by the cell. This is especially noticeable in the cells of epithelial tissues, which delimit different environments of the body.

Microtubules are involved in the transport of substances within the cell. Protein molecules in the form of short chains are connected (associated) with the microtubule wall at one of their ends in the form of short chains, which are capable of changing their spatial configuration (protein conformation) under appropriate conditions. In the neutral position, the chain lies parallel to the wall surface. In this case, the free end of the chain can bind to particles that are in the surrounding glycocalyx.

After binding the particle, the protein changes its configuration and deviates from the wall, thereby moving the blocked particle along with it. The deflected chain passes the particle to the one hanging above it, which also deflects and passes the particle further. Due to the presence of conformable outer chains, microtubules provide the main flows of intracellular active transport.

The structure of the microtubule wall can change under various influences on them.

In such cases, intracellular transport may be impaired. Among the blockers of microtubules and, accordingly, intracellular transport is, in particular, the alkaloid colchicine.

–  –  –

Intermediate filaments Intermediate filaments 8-10 nm thick are represented in the cell by long protein molecules. They are thinner than microtubules, but thicker than microfilaments, for which they got their name (Fig. 26).

Intermediate filament proteins belong to four main groups.

Some of their characteristics are given in table. 5. Each group, in its own Fig. 26. Intermediate filaments in a cell (according to K. de Duve, with changes) turn, includes several proteins (for example, more than 20 types of keratins are known).

Each protein is an antigen, so an appropriate antibody can be created against it. If the antibody is labeled in some way (for example, by attaching a fluorescent label to it), then, by introducing it into the body, it is possible to detect the localization of this protein. Proteins of intermediate filaments retain their specificity even with significant changes in the cell, including its malignancy. Therefore, using specific labeled antibodies to intermediate filament proteins, it is possible to establish which cells were the primary source of the tumor.

Microfilaments Microfilaments are protein filaments about 4 nm thick. Most of them are made up of molecules

–  –  –

actins, of which about 10 species have been identified. In addition, actin filaments can be grouped into bundles that form the proper supporting structures of the cytoskeleton.

Actin in the cell exists in two forms: monomeric (globular actin) and polymerized (fibrillar actin). In addition to actin itself, other peptides can also take part in the construction of microfilaments: troponins and tropomyosin (Fig. 27).

Polymeric actin filaments are able to form complexes with polymeric molecules of myosin protein. When myosin is present in the hyaloplasm as monomers, it does not enter into a complex with actin. The polymerization of myosin requires calcium ions. Its binding occurs with the participation of troponin C (by the name of the calcium element), its release - with the participation of troponin I (an inhibitory molecule), complexation with tropomyosin - with the participation of troponin T. After the actin-myosin complex arises, actin and myosin become able to move into it longitudinally relative to each other. If the ends of the complex are fastened to some other intracellular structures, the latter approach each other. This underlies muscle contraction.

There are especially many microfilaments in the area of ​​the cytoplasm related to the surface complex. Being connected to the plasmalemma, they are able to change its configuration. This is important for ensuring the entry of substances into the cell through pinocytosis and phagocytosis. The same mechanism is used by the cell in the formation of outgrowths of its surface - lamellipodia. The cell can be fixed by lamellopodia to the surrounding substrate and move to a new location.

CELL CENTER

The cell center (Fig. 28) is formed by two centrioles (diplosome) and a centrosphere. The organelle got its name due to the fact that it is usually located in the deep sections of the cytoplasm, often near the nucleus or near the emerging surface of the Golgi complex. Both centrioles of the diplosome are at an angle to each other. The main function of the cell center is the assembly of microtubules.

Rice. 28. Cell Center:

1 - triplets of microtubules; 2 - radial spokes; 3 - the central structure of the "cart wheel"; 4 - satellite; 5 - lysosome; b – dictyosomes of the Golgi complex; 7 - bordered vesicle; 8 - cistern of granular endoplasmic reticulum; 9 - tanks and tubules of the agranular endoplasmic reticulum; 10 - mitochondrion; 11 - residual body; 12 microtubules; 13 - karyoteka (according to R. Krstic, with changes)

–  –  –

Each centriole is a cylinder, the wall of which, in turn, consists of nine complexes of microtubules about 0.5 µm long and about 0.25 µm in diameter. Each complex consists of three microtubules and is therefore called a triplet. The triplets, located relative to each other at an angle of about 50°, consist of three microtubules (from inside to outside): complete A and incomplete B and C, each with a diameter of about 20 nm. Two handles extend from tube A. One of them is directed to the tube C of the neighboring triplet, the other is directed to the center of the cylinder, where the inner handles form the shape of a star or wheel spokes. Each microtubule has a typical structure (see earlier).

The centrioles are mutually perpendicular. One of them rests with its end against the side surface of the other. The first is called the daughter, the second is the parent.

The daughter centriole arises from the doubling of the mother centriole. The maternal centriole is surrounded by an electron-dense rim formed by spherical satellites connected by a dense material to the outer side of each triplet. The middle part of the maternal centriole may also be surrounded by a complex of fibrillar structures called a halo. Triplets of microtubules are united at the base of the maternal centriole by electron-dense clusters - roots (appendages).

Towards the end of the satellites and to the halo region, tubulins are transported through the cytoplasm, and it is here that the assembly of microtubules occurs. Once assembled, they are separated and sent to different parts of the cytoplasm to take their place in the structures of the cytoskeleton. It is possible that satellites are also a source of material for the formation of new centrioles during their replication. The region of hyaloplasm around the centrioles and satellite is called the centrosphere.

Centrioles are self-regulating structures that double in the cell cycle (see Cell Cycle section). When doubling, at first, both centrioles diverge, and a small centriole formed by nine single microtubules appears perpendicular to the basal end of the maternal one. Then two more are attached to each of them by self-assembly from tubulin. Centrioles are involved in the formation of the basal bodies of cilia and flagella and in the formation of the mitotic spindle.

RIBOSOME

Ribosomes (Fig. 29) are bodies 20 x 30 nm in size (sedimentation constant 80). The ribosome consists of two subunits - large and small. Each subunit is a complex of ribosomal RNA (rRNA) with proteins. The large subunit (sedimentation constant 60) contains three different rRNA molecules associated with 40 protein molecules; the small one contains one rRNA molecule and 33 protein molecules. Synthesis of rRNA is carried out on loops of chromosomes - nucleolar organizers G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 49 (in the area of ​​the nucleolus). The assembly of ribosomes is carried out in the region of the pores of the karyotheca.

The main function of ribosomes is to assemble protein molecules from amino acids delivered to them by transfer RNA (tRNA). Between the subunits of the ribosome there is a gap in which the messenger RNA (mRNA) molecule passes, and on the large subunit (Fig. 29.

Ribosome:

I - small subunit; II - large subunit; III - association of subunits; upper and lower rows - images in different projections (according to B. Alberts et al., with changes) of the groove in which the emerging protein chain is located and along which it slides. Amino acids are assembled according to the sequence of nucleotides in the mRNA chain. In this way, the transmission of genetic information is carried out.

Ribosomes can be found in the hyaloplasm singly or in groups in the form of rosettes, spirals, curls. Such groups are called polyribosomes (polysomes). Thus, an mRNA molecule can stretch over the surface of not only one, but several adjacent ribosomes. A significant part of the ribosomes is attached to membranes: to the surface of the endoplasmic reticulum and to the outer membrane of the karyotheca.

Free ribosomes synthesize a protein necessary for the life of the cell itself, attached - a protein to be removed from the cell.

The number of ribosomes in a cell can reach tens of millions.

MEMBRANE ORGANELLES

Each membrane organelle represents a structure of the cytoplasm bounded by a membrane. As a result, a space is formed inside it, delimited from the hyaloplasm. The cytoplasm is thus divided into separate compartments with their own properties - compartments (English compartment - compartment, compartment, compartment).

The presence of compartments is one of the important features of eukaryotic cells.

Membrane organelles include mitochondria, endoplasmic reticulum (ER), Golgi complex, lysosomes, and peroxisomes. Some authors also classify microvilli as common organelles. The latter are sometimes referred to as special organelles, but in fact they are found on the surface of any cell and will be described together with the surface complex of the cytoplasm. K. de Duve combined EPS, the Golgi complex, lysosomes and peroxisomes with the concept of vacuum (see the section "Golgi Complex"),

MITOCHONDRIA

Mitochondria are involved in the processes of cellular respiration and convert the energy that is released in the process into a form available for use by other cell structures. Therefore, the figurative name "energy stations of the cell", which has become trivial, has been assigned to them.

Mitochondria, unlike other organelles, have their own genetic system necessary for their self-reproduction and protein synthesis. They have their own DNA, RNA and ribosomes, which differ from those in the nucleus and other sections of the cytoplasm of their own cells. At the same time, mitochondrial DNA, RNA, and ribosomes are very similar to prokaryotic ones. This was the impetus for the development of the symbiotic hypothesis, according to which mitochondria (and chloroplasts) arose from symbiotic bacteria (L. Margulis, 1986). Mitochondrial DNA is circular (like in bacteria), G.L. Bilic. V.A. Kryzhanovsky. Biology. Full course. In 3 volumes. Volume 1. Anatomy. - M .: LLC "Publishing House" ONIX 21st century ". 2004. - 864 p: ill.

Yanko Slava (Fort/Da Library) || http://yanko.lib.ru 50 it accounts for about 2% of cell DNA.

Mitochondria (and chloroplasts) are able to multiply in the cell by binary fission. Thus, they are self-replicating organelles. At the same time, the genetic information contained in their DNA does not provide them with all the proteins necessary for complete self-reproduction; some of these proteins are encoded by nuclear genes and enter the mitochondria from the hyaloplasm. Therefore, mitochondria in relation to their self-reproduction are called semi-autonomous structures.

In humans and other mammals, the mitochondrial genome is inherited from the mother:

When an egg is fertilized, the mitochondria do not allow sperm to enter it. Such a seemingly abstract, purely theoretical proposition has found a purely practical application in recent years: the study of the sequence of DNA components in mitochondria helps to reveal genealogical relationships along the female line. This is essential for personal identification. Historical and ethnographic comparisons were also interesting. So, in ancient Mongolian legends, it was stated that the three branches of this people descended from three mothers; studies of mitochondrial DNA have indeed confirmed that members of each branch have such special features that others do not.

The main properties of mitochondria and the functions of their structural components are summarized in Table. 6.

In a light microscope, mitochondria look like rounded, elongated or rod-shaped structures 0.3–5 µm long and 0.2–1 µm wide. Each mitochondrion is formed by two membranes - external and internal (Fig. 30).

–  –  –

genome translation of mitochondria Between them is an intermembrane space 10 - 20 nm wide.

The outer membrane is smooth, while the inner one forms numerous cristae, which may look like folds and ridges. Sometimes cristae look like tubules with a diameter of 20 nm. This is observed in cells that synthesize steroids (here, mitochondria not only provide respiration processes, but also participate in the synthesis of these substances).

Thanks to the cristae, the area of ​​​​the inner membrane increases significantly.

The space bounded by the inner membrane is filled with colloidal mitochondrial matrix. It has a fine-grained structure and contains many different enzymes. The matrix also contains its own genetic apparatus of mitochondria (in plants, in addition to mitochondria, DNA is also contained in chloroplasts).

From the side of the matrix, many electron-dense submitochondrial elementary particles (up to 4000 per 1 μm2 of the membrane) are attached to the surface of the cristae. Each of them has the shape of a mushroom (see Fig. 30).

Rice. 30. Mitochondria:

I - general scheme of the structure: 1 - outer membrane; 2 - inner membrane;

3 - cristae; 4 - matrix; II - diagram of the structure of the crista: 5 - fold of the inner membrane; 6 - mushroom bodies (according to B. Alberts et al. and K. de Duve, with changes) A ​​round head with a diameter of 9-10 nm is attached to the inner membrane by means of a thin stem with a diameter of 3-4 nm. These particles contain ATPase enzymes that directly provide for the synthesis and breakdown of ATP. These processes are inextricably linked with the tricarboxylic acid cycle (the citric acid cycle, or the Krebs cycle, see the section "Basic reactions of tissue metabolism").

The number, size and location of mitochondria depend on the function of the cell, in particular on its need for energy and on the place where energy is spent. So, in one hepatic cell their number reaches 2500. Many large mitochondria are contained in cardiomyocytes and myosymplasts of muscle fibers. In sperm, mitochondria rich in cristae surround the axoneme of the intermediate part of the flagellum. There are cells in which mitochondria are extremely large. Such a mitochondrion can branch and form a three-dimensional network. This is shown by reconstructing the cell structure from separate successive sections. On a flat section, only parts of this mitochondrion are visible, which creates the impression of their multiplicity (Fig. 31).

–  –  –

ENDOPLASMIC RETICULUM

The endoplasmic reticulum (ER), or, as it is often called, the endoplasmic reticulum (ER), is a single continuous compartment, bounded by a membrane that forms many invaginations and folds (Fig. 32). Therefore, in electron microscopic photographs, the endoplasmic reticulum looks like many tubules, flat or rounded cisterns, membrane vesicles. On the membranes of the EPS, various primary synthesis of substances necessary for the life of the cell takes place. They can be conditionally called primary because the molecules of these substances will undergo further chemical transformations in other compartments of the cell.

Rice. 32. Endoplasmic reticulum:

1 - tubules of a smooth (agranular) network; 2 - tanks of a granular network; 3

Outer nuclear membrane covered with ribosomes; 4 – pore complex; five

Inner nuclear membrane (according to R. Krstic, with changes) Most substances are synthesized on the outer surface of the EPS membranes. Then these substances are transported through the membrane into the compartment and there they are transported to the sites of further biochemical transformations, in particular to the Golgi complex.

At the ends of the EPS tubules, they accumulate and then separate from them in the form of transport bubbles. Each vesicle is thus surrounded by a membrane and travels in the hyaloplasm to its destination. As always, microtubules take part in the transport.

Among the products synthesized on EPS membranes, we should especially note those substances

–  –  –

which serve as material for the assembly of cell membranes (the final assembly of membranes is carried out in the Golgi complex).

There are two types of EPS: granular (granular, rough) and agranular (smooth). Both are the same structure.

The outer side of the membrane of the granular ER, facing the hyaloplasm, is covered with ribosomes. Therefore, under light microscopy, the granular endoplasmic reticulum looks like a basophilic substance, giving a positive color for RNA. This is where protein synthesis takes place. In cells specialized in protein synthesis, the granular endoplasmic reticulum looks like parallel fenestrated (fenestrated) lamellar structures communicating with each other and with the perinuclear space, between which lies many free ribosomes.

The surface of the smooth ER is devoid of ribosomes. The network itself is a set of small tubes with a diameter of about 50 nm each. Glycogen granules are often located between the tubules. In some cells, a smooth network forms a pronounced labyrinth (for example, in hepatocytes, in Leydig cells), in others, circular plates (for example, in oocytes).

Carbohydrates and lipids are synthesized on the membranes of the smooth network, among them glycogen and cholesterol.

The smooth network is also involved in the synthesis of steroid hormones (in Leydig cells, in cortical endocrinocytes of the adrenal gland). Smooth ER is also involved in the release of chloride ions in the parietal cells of the epithelium of the gastric glands. Being a depot of calcium ions, the smooth endoplasmic reticulum is involved in the contraction of cardiomyocytes and skeletal muscle fibers. It also delimits future platelets in megakaryocytes. Its role is extremely important in the detoxification by hepatocytes of substances that come from the intestinal cavity through the portal vein into the hepatic capillaries.

Through the lumens of the endoplasmic reticulum, the synthesized substances are transported to the Golgi complex (but the lumens of the network do not communicate with the lumens of the cisterns of the latter). Substances enter the Golgi complex in vesicles, which are first detached from the network, transported to the complex, and finally merge with it.

From the Golgi complex, substances are also transported to their places of use in membrane vesicles. It should be emphasized that one of the most important functions of the endoplasmic reticulum is the synthesis of proteins and lipids for all cell organelles.

GOLGI COMPLEX

The Golgi complex (Golgi apparatus, intracellular reticular apparatus, CG) is a collection of tanks, vesicles, plates, tubules, sacs. In a light microscope, it looks like a grid, but in reality it is a system of tanks, tubules and vacuoles.

Most often, three membrane elements are detected in CG: flattened sacs (cistern), vesicles and vacuoles (Fig. 33). The main elements of the Golgi complex are dictyosomes (Greek dyction - network). Their number varies in different cells from one to several hundred.

–  –  –

Dictyosomes are interconnected by channels. A single dictyosome is most often cup-shaped. It has a diameter of about 1 µm and contains 4–8 (average 6) flattened cisterns lying in parallel and permeated with pores. The ends of the tanks are widened. Bubbles and vacuoles are split off from them, surrounded by a membrane and containing various substances.

Many membranous vesicles (including bordered ones) have a diameter of 50 nm. Larger secretory granules have a diameter of 66 to 100 nm. Some of the vacuoles contain hydrolytic enzymes, these are precursors of lysosomes.

The widest flattened tanks face the EPS. Transport bubbles, carrying substances - products of primary syntheses, are attached to these tanks. In the tanks, the synthesis of polysaccharides continues, complexes of proteins, carbohydrates and lipids are formed, in other words, the brought macromolecules are modified. Here, the synthesis of polysaccharides, the modification of oligosaccharides, the formation of protein-carbohydrate complexes, and the covalent modification of transported macromolecules take place.

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G.L. BILICH, V.A. KRYZHANOVSKY I ι I 1 _ I "V onyx \ G.L. BILICH, V.A. KRYZHANOVSKII OGIA COMPLETE COURSE In three volumes 1 volume ANATOMY MOSCOW.ONYX 21 CENTURY" 2002 [- AND UDC 57 (075.3) BBK 28ya729 B61 Reviewers : Doctor of Medical Sciences, Professor, Academician of the Russian Academy of Natural Sciences L. E. Etingen, Doctor of Biological Sciences, Professor A. G. Bulychev Authors: Bilich Gabriel Lazarevich, Academician of the Russian Academy of Natural Sciences, Vice-President of the National Academy of Juvenology, Academician of the International Academy Sci., Doctor of Medical Sciences, Professor, Director of the North-Western Branch of the East European Institute of Psychoanalysis Author of 306 published scientific papers, including 8 textbooks, 14 study guides, 8 monographs Kryzhanovsky Valery Anatolyevich, Candidate of Biological Sciences, lecturer at the Moscow Medical Academy named after I. M. Sechenov, author of 39 published scientific papers and two textbooks Bilich G. L., Kryzhanovsky V. A. B 61 Biology. Complete course. In 3 volumes. Volume 1. Anatomy. - M. :000" Publishing house "ONIX 21st century", 2002. - 864 p., ill. ISBN 5-329-00375-X ISBN 5-329-00601-5 (Volume 1. Anatomy) Detailed modern data on the structure and vital activity of cells and tissues are presented, all cellular components are described. The main functions of cells are considered: metabolism, including respiration, synthetic processes, cell division (mitosis, meiosis). A comparative description of eukaryotic (animal and plant) and prokaryotic cells, as well as viruses, is given. Photosynthesis is considered in detail. Particular attention is paid to classical and modern genetics. The structure of tissues is described. A significant part of the book is devoted to the functional human anatomy. The book is intended for students of schools with in-depth study of biology, applicants and students of higher educational institutions studying in areas and specialties in the field of medicine, biology, ecology, veterinary medicine, as well as for school teachers, graduate students and university professors. UDC 57(075.3) BBC 28ya729 ISBN 5-329-00375-X © G. L. Bilich, V. A. Kryzhanovsky, 2002 ISBN 5-329-00601-5 (Volume 1. Anatomy) © ONIKS Publishing House LLC 21st century”, 2002 Introduction School and university programs in biology and, accordingly, textbooks lag behind the rapidly developing science. However, the requirements for applicants and students are steadily growing, and a young man, especially an inquisitive and talented one, needs additional literature that would correspond to the current state of the discipline. So far, there is no such literature. The authors tried to fill this gap and create a book that will be in demand in the 21st century. To what extent this has been achieved, we leave it to the reader to judge. Biology is a set of sciences about wildlife, about the structure, functions, origin, development, diversity and distribution of organisms and communities, their relationships and connections with the external environment. Being unified, biology includes two sections: morphology and physiology. Morphology studies the form and structure of living beings; physiology - the vital activity of organisms, the processes occurring in their structural elements, the regulation of functions. Morphology includes normal anatomy proper (the science of the macroscopic structure of organisms, their organs, apparatuses and systems), histology (the science of the microscopic structure of tissues and organs) and cytology (the science that studies the structure, chemical composition, development and functions of cells, the processes of their reproduction, recovery, adaptation to constantly changing environmental conditions), embryology (the science of the development of organisms). An important branch of biology is genetics, the science of heredity and variability of organisms. The concept of the three-volume book “Biology. Full course "- the study of the biological structure at various hierarchical levels in close connection with the function performed. Illustrative material (more than a thousand original drawings, diagrams and tables), which facilitates the assimilation of the material, was selected based on these considerations. The authors consider it their pleasant duty to express their heartfelt gratitude for their help in preparing the manuscript for publication to P. I. Kurenkov, G. G. Galashkina, and E. Yu. Zigalova. Authors 3 CELL In the process of studying a person, his structures are divided into cells, tissues, morphofunctional units of organs, organs, systems and apparatuses of organs that form the body (Table 1). However, the reader should be cautioned against taking this division literally. The organism is one, it can exist as such only thanks to its integrity. The body is integral, but organized, like many complex systems, according to a hierarchical principle. It is these structures that form its constituent elements. Table 1 Hierarchical levels of body structure APPARATUS Cells and their derivatives Tissues (epithelial, internal environment, muscular, neutral) 1 Morphofunctional units of organs X Organs Apparatuses and systems of organs - Digestive Respiratory Cardiovascular Hematopoietic and immune Nervous (animal and vegetative) A single organism The study of each level of organization of the living requires its own approaches and methods. The first level of organization of living things - cells - studies the branch of biological sciences called cytology. CELL THEORY The development of cytology is associated with the creation and improvement of optical devices that make it possible to examine and study cells. In 1609 - 1610. Galileo Galilei designed the first microscope, but only in 1624 did he improve it so that it could be used. This microscope magnified 35 - 40 times. A year later, I. Faber gave the device the name “microscope”. In 1665, Robert Hooke first saw cells in a cork, which he gave the name "cell" - "cell". In the 70s. 17th century Marcello Malpighi described the microscopic structure of some plant organs. Thanks to the improvement of the microscope by Anton van Leeuwenhoek, it became possible to study cells and the detailed structure of organs and tissues. In 1696, his book "The Secrets of Nature, discovered with the help of the most perfect microscopes" was published. Leeuwenhoek was the first to consider and describe erythrocytes, spermatozoa, discovered the hitherto unknown and mysterious world of microorganisms, which he called ciliates. Leeuwenhoek is rightfully considered the founder of scientific microscopy. In 1715 H.G. Gertel was the first to use a mirror to illuminate microscopic objects, but only a century and a half later E. Abbe created a system of lighting lenses for a microscope. In 1781, F. Fontana was the first to see and draw animal cells with their nuclei. In the first half of the XIX century. Jan Purkinje improved the microscopic technique, which enabled him to describe the cell nucleus (“germinal vesicle”) and cells in various animal organs. Jan Purkinje was the first to use the term "protoplasm". 5 R. Brown described the nucleus as a permanent structure and proposed the term "nucleus" - "nucleus". In 1838, M. Schleiden created the theory of cytogenesis (cell formation). His main merit is to raise the question of the origin of cells in the body. Based on the work of Schleiden, Theodor Schwann created the cell theory. In 1839, his immortal book "Microscopic investigations on the conformity in the structure and growth of animals and plants" was published. The main starting points of the cell theory were the following: - all tissues consist of cells; - cells of plants and animals have common structural principles, since they arise in the same ways; - each individual cell is independent, and the activity of the body is the sum of the vital activity of individual cells. Rudolf Virchow had a great influence on the further development of cell theory. He not only brought together all the numerous disparate facts, but also convincingly showed that cells are a permanent structure and arise only by multiplying their own kind - "each cell from a cell" ("omnia cellula e cellulae"). In the second half of the XIX century. the concept of the cell as an elementary organism arose (E. Brücke, 1861). In 1874, J. Carnoy introduced the concept of "cell biology", thereby laying the foundation for cytology as a science of the structure, function and origin of cells. In 1879 - 1882. W. Flemming described mitosis, in 1883 W. Waldeyer introduced the concept of "chromosomes", a year later O. Hertwig and E. Strasburger simultaneously and independently of each other hypothesized that hereditary traits are contained in the nucleus. End of the 19th century was marked by the discovery of phagocytosis by Ilya Mechnikov (1892). 6 At the beginning of the 20th century. R. Garrison and A. Carrel developed methods for culturing cells in a test tube like unicellular organisms. In 1928 - 1931. E. Ruska, M. Knoll and B. Borrie constructed an electron microscope, thanks to which the true structure of the cell was described and many previously unknown structures were discovered. A. Claude in 1929 - 1949 first used the electron microscope to study cells and developed methods for cell fractionation using ultracentrifugation. All this allowed us to see the cell in a new way and interpret the collected information. The cell is the elementary unit of all living things, because it has all the properties of living organisms: a highly ordered structure, receiving energy from outside and using it to perform work and maintain order (overcoming entropy), metabolism, active response to stimuli, growth, development, reproduction, doubling and transfer of biological information to descendants, regeneration, adaptation to the environment. The cellular theory in the modern interpretation includes the following main provisions: - the cell is the universal elementary unit of the living; - the cells of all organisms are fundamentally similar in structure, function and chemical composition; - cells reproduce only by dividing the original cell; - cells store, process and realize genetic information; - multicellular organisms are complex cellular ensembles that form integral systems; - it is thanks to the activity of cells in complex organisms that growth, development, metabolism and energy are carried out. 7 In the XX century. Nobel Prizes were awarded for discoveries in the field of cytology and related sciences. Among the laureates were: - 1906 Camillo Golgi and Santiago Ramón y Cajal for discoveries in the field of neuronal structure; - 1908 Ilya Mechnikov and Paul Ehrlich for their discoveries of phagocytosis (Mechnikov) and antibodies (Erlich); - 1930 Karl Landsteiner for the discovery of blood groups; - 1931 Otto Warburg for the discovery of the nature and mechanisms of action of the respiratory enzymes of cytochrome oxidases; - 1946 Hermann Moeller for the discovery of mutations; - 1953 Hans Krebs for the discovery of the citric acid cycle; - 1959 Arthur Kornberg and Severo Ochoa for the discovery of the mechanisms of DNA and RNA synthesis; - 1962 Francis Crick, Maurice Wilkinson and James Watson for their discovery of the molecular structure of nucleic acids and their importance for the transmission of information in living systems; - 1963 Francois Jacob, Andre Lvov and Jacques Monod for the discovery of the mechanism of protein synthesis; - 1968 Har Gobind Korana, Marshall Nirenberg and Robert Holley for deciphering the genetic code and its role in protein synthesis; - 1970 Julius Axelrod, Bernard Katz and Ulf von Euler for the discovery of humoral neurotransmitters of nerve endings and the mechanism of their storage, release and inactivation; - 1971 Earl Sutherland for the discovery of the cAMP second messenger (cAMP) and its role in the mechanism of action of hormones; - 1974 Christian de Duve, Albert Claude and Georges Palade for discoveries concerning the structural and functional organization of the cell (ultrastructure and function of lysosomes, Golgi complex, endoplasmic reticulum). 8 PROKARYOTIC AND EUKARYOTIC CELLS Currently, prokaryotic and eukaryotic organisms are distinguished. The former include blue-green algae, actinomycetes, bacteria, spirochetes, mycoplasmas, rickettsia and chlamydia, the latter include most algae, fungi and lichens, plants and animals. Unlike a prokaryotic cell, a eukaryotic cell has a nucleus bounded by a sheath of two membranes and a large number of membrane organelles. More detailed differences are presented in Table. 2. CHEMICAL ORGANIZATION OF THE CELL Of all the elements of the periodic system, D.I. Mendeleev, 86 constantly present in the human body were found, of which 25 are necessary for normal life, 18 of which are absolutely necessary, and 7 are useful. Professor D.R. Williams called them the elements of life. The composition of the substances involved in the reactions associated with the vital activity of the cell includes almost all known chemical elements, and four of them account for about 98% of the mass of the cell. These are oxygen (65 - 75%), carbon (15 - 18%), hydrogen (8 - 10%) and nitrogen (1.5 - 3.0%). The remaining elements are divided into two groups: macroelements (about 1.9%) and microelements (about 0.1%). Macroelements include sulfur, phosphorus, chlorine, potassium, sodium, magnesium, calcium and iron, microelements - zinc, copper, iodine, fluorine, manganese, selenium, cobalt, molybdenum, strontium, nickel, chromium, vanadium, etc. Despite very low content, trace elements play an important role. They affect metabolism. Without them, the normal functioning of each cell individually and the organism as a whole is impossible. The cell is made up of inorganic and organic substances. Water predominates among the inorganic, its relative amount is from 70 to 80%. 9 3- for a o Η h * i u S1 I Η o i o. ev and * i and o V I Η o i o. ev and ol v i i ev i a i l a i) S i l Η i ev Lev X o b s p - ■ή GO X k t th iot- α. φ s re 3 ^ 1° lii SI 1 go s ία- SG ϋ ? o m 4 r" r? O ρ CO o S a) to I s ro Ο * .. with ι w (DID ara. o O ° 5 No. Ρ >*CD "ς ^1 OS og CD J Ρ og 5" t- s § CD J 1 I GO -0 I in * "o ° CO UC o a-Sch ^c η Ss so with 25 5 x ° t- ϊ th \u003d rgio with sh o d! | O\u003e 1 with t-sh," 2 & .° 8 2o JLfco "o fcfc. 5< Г) S t- s о сЗ |g S| go .ι °- о g! oof! «Is 2 >, o: ;ss l: fcfc si ro ^ p 82 |a 58 ι - ι S CD O CD C O co s ΪΙΟ ro 5 β- Ο. O O So |δϋ05 Q eg l + ΙΟ) g £ CD > ■ 5 "as o ctI &.&.Ϊ I CD 3" s" ■ CO ! 10 Water is a universal solvent, all biochemical reactions in the cell take place in it, with the participation of water, its thermoregulation is carried out. Substances that dissolve in water (salts, bases, acids, proteins, carbohydrates, alcohols, etc.) are called hydrophilic. Hydrophobic substances (fats and fat-like) do not dissolve in water. There are organic substances with elongated molecules , in which one end is hydrophilic, the other is hydrophobic; they are called amphipathic. An example of amphipathic substances are phospholipids involved in the formation of biological membranes. Inorganic substances (salts, acids, bases, positive and negative ions) range from 1.0 to 1, 5% of the cell mass Among organic substances, proteins (10 - 20%), fats, or lipids (1 - 5%), carbohydrates (0.2 - 2.0%), nucleic acids (1 - 2%) predominate. low molecular weight substances in the cell does not exceed 0.5%. rum, which consists of a large number of repeating units (monomers). Protein monomers - amino acids (there are 20 of them) simultaneously have two active atomic groups - an amino group (it gives the amino acid molecule the properties of a base) and a carboxyl group (it tells the molecule the properties of an acid) (Fig. 1). Amino acids are interconnected by peptide bonds, forming a polypeptide chain (the primary structure of a protein) (Fig. 2). It twists into a spiral, which, in turn, represents the secondary structure of the protein. Due to a certain spatial orientation of the polypeptide chain, a tertiary structure of the protein arises, which determines the specificity. 1. The general scheme of the amino acid: R is the radical by which amino acids differ from each other; in the frame - the common part for all amino acids 11 Methine groups CH N-terminus H,N-CH-CO-NH * i, Side radicals Fig. 2. A fragment of a polypeptide (according to N. A. Tyukavkina and Yu. I. Baukov, with changes) and the biological activity of a protein molecule. Several tertiary structures combine to form a quaternary structure. Proteins perform essential functions. Enzymes - biological catalysts that increase the rate of chemical reactions in the cell hundreds of thousands - millions of times, are proteins. Proteins, being part of all cellular structures, perform a plastic (building) function. They form the cellular skeleton. Cell movements are also carried out by special proteins (actin, myosin, dynein). Proteins provide transport of substances into the cell, out of the cell and within the cell. Antibodies, which, along with regulatory functions, also perform protective functions, are also proteins. And finally, proteins are one of the sources of energy. Carbohydrates are divided into monosaccharides and polysaccharides. Polysaccharides, like proteins, are built from monomers - monosaccharides. Among the monosaccharides in the cell, the most important are glucose (containing six carbon atoms) and pentose (five carbon atoms). Pentoses are part of nucleic acids. Monosaccharides dissolve well in water, polysaccharides - poorly. In animal cells, polysaccharides are represented by glycogen, in plant cells - mainly by soluble starch and 3. The general formula of triacylglycerol (fat or oil), where R1, R2, R3 are fatty acid residues insoluble by cellulose, hemicellulose, pectin, etc. Carbohydrates are a source of energy. Complex carbohydrates combined with proteins (glycoproteins) and/or fats (glycolipids) are involved in the formation of cell surfaces and cell interactions. Lipids include fats and fat-like substances. Fat molecules are built from glycerol and fatty acids (Fig. 3). Fat-like substances include cholesterol, some hormones, and lecithin. Lipids, which are the main component of cell membranes (they are described below), thereby perform a building function. They are the most important source of energy. So, if with the complete oxidation of 1 g of protein or carbohydrates, 17.6 kJ of energy is released, then with the complete oxidation of 1 g of fat - 38.9 kJ. Nucleic acids are polymeric molecules formed by monomers - nucleotides, each of which consists of a purine or pyrimidine base, a pentose sugar and a phosphoric acid residue. In all cells, there are two types of nucleic acids: deoxyribonucleic (DNA) and ribonucleic (RNA), which differ in the composition of bases and sugars (Table 3, Fig. 4). The RNA molecule is formed by one polynucleotide chain (Fig. 5). The DNA molecule consists of two multidirectional polynucleotide chains twisted one around the other in the form of a double helix. Each nucleotide consists of a nitrogenous base, a sugar, and a phosphoric acid residue. In this case, the bases are located 13 (T) O "ι I 0 \u003d P ~ 0-CH I O" R4 R1 he he * "end Fig. 4. The structure of nucleic acid molecules: I - RNA; II - numbering of carbon atoms in the pentose cycle; III - DNA. An asterisk (") indicates differences in the structure of DNA and RNA. Valence bonds are shown in a simplified way: A - adenine; T - thymine; C - cytosine; G - guanine; U - uracil 14 Fig. 5. Spatial structure of nucleic acids: I - RNA; II-DNA; ribbons - sugar-phosphate backbones; A, C, G, T, U - nitrogenous bases, the lattices between them - hydrogen bonds (according to B. Apberts et al., with changes) inside the double helix, and the sugar-phosphate skeleton - outside. The nitrogenous bases of both chains are interconnected by complementary hydrogen bonds, while adenine is connected only with thymine, and cytosine with guanine. Depending on the number of the atom in relation to the bond with the base, the ends of the chain are designated as 5 "and 3" (see Fig. 4 and 5). DNA carries genetic information encoded by the sequence of nitrogenous bases. It determines the specificity of the proteins synthesized by the cell, i.e. the sequence of amino acids in the polypeptide chain. Together with DNA, genetic information is transmitted to daughter cells, determining shaya (in interaction with environmental conditions) all the properties of the cell. DNA is found in the nucleus and mitochondria, and in plants in chloroplasts. All biochemical reactions in the cell are strictly structured and are carried out with the participation of highly specific biocatalysts - enzymes, 15 or enzymes (Greek en - in, zyme - fermentation, leaven), - proteins, which, when combined with biological molecules - substrates, reduce the activation energy required for the implementation of a particular reaction (activation energy is the minimum amount of energy required for a molecule to enter into a chemical reaction). Enzymes speed up the reaction by 10 orders of magnitude (1010 times). The names of all enzymes are composed of two parts. The first contains an indication either of the substrate, or of the action, or of both. The second part is the ending, it is always represented by the letters "aza". So, the name of the enzyme "succinate dehydrogenase" means that it acts on the compounds of succinic acid ("succinate-"), taking away hydrogen from them ("-dehydrogen-"). According to the general type of action, enzymes are divided into 6 classes. Oxireductases catalyze redox reactions, transferases are involved in the transfer of functional groups, hydrolases provide hydrolysis reactions, lyases add groups to double bonds, isomerases transfer compounds to another isomeric form, and ligases (not to be confused with lyases! ) link molecular groups in the chain. The basis of any enzyme is protein. At the same time, there are enzymes that do not have catalytic activity until a simpler non-protein group, the coenzyme, is added to the protein base (apoenzyme). Sometimes coenzymes have their own names, sometimes they are denoted by letters. Often, the composition of coenzymes includes substances now called vitamins. Many vitamins are not synthesized in the body and therefore must be obtained from food. With their deficiency, diseases (avitaminosis) occur, the symptoms of which, in fact, are manifestations of insufficient activity of the corresponding enzymes. 16 Several coenzymes play a key role in many important biochemical reactions. An example is coenzyme A (CoA), which ensures the transfer of acetic acid groups. The coenzyme nicotinamide adenine dinucleotide (abbreviated as NAD) provides the transfer of hydrogen ions in redox reactions; the same is true of nicotinamide adenine dinucleotide phosphate (NADP), flavin adenine dinucleotide (FAD), and a number of others. By the way, nicotinamide is one of the vitamins. STRUCTURE OF AN ANIMAL CELL A cell is the main structural and functional unit of living organisms, carrying out growth, development, metabolism and energy, storing, processing and realizing genetic information. A cell is a complex system of biopolymers, separated from the external environment by a plasma membrane (cytolemma, plasmalemma) and consisting of a nucleus and cytoplasm, in which organelles and inclusions are located. The French scientist, Nobel Prize winner A. Lvov, based on the achievements of modern cytology, wrote: “Considering the living world at the cellular level, we find its unity: the unity of structure - each cell contains a nucleus immersed in the cytoplasm; unity of function - metabolism is basically similar in all cells; unity of composition - the main macromolecules in all living beings consist of the same small molecules. To build a huge variety of living systems, nature uses a limited number of building blocks. However, different cells also have specific structures. This is due to the performance of their special functions. The sizes of human cells vary from a few micrometers (for example, small lymphocytes - about 7) 17 to 200 microns (ovum). Recall that one micrometer (µm) = 10 6 m; 1 nanometer (nm) = 109 m; 1 angstrom (E) = 1010 m. The shape of the cells is varied. They can be spherical, ovoid, fusiform, flat, cubic, prismatic, polygonal, pyramidal, stellate, scaly, process, amoeboid, etc. The main functional structures of the cell are its surface complex, cytoplasm and nucleus. The surface complex includes the glycocalyx, the plasma membrane (plasmalemma), and the cortical layer of the cytoplasm. It is easy to see that there is no sharp delimitation of the surface complex from the cytoplasm. In the cytoplasm, hyaloplasm (matrix, cytosol), organelles and inclusions are isolated. The main structural components of the nucleus are the karyolemma (karyotheca), nucleoplasm and chromosomes; loops of some chromosomes can intertwine, and in this area a nucleolus is formed. Chromatin is often referred to as the structural elements of the nucleus. However, by definition, chromatin is the substance of chromosomes. The plasmalemma, karyolemma and part of the organelles are formed by biological membranes. The main structures that form the cell are listed in Table. 4 and are presented in fig. 6. BIOLOGICAL MEMBRANES The structure of biological membranes is most fully reflected in the fluid-mosaic model, the initial version of which was proposed in 1972 by G. Nicholson and S. Singer. The membrane consists of two layers of amphipathic lipid molecules (bilipid layer, or bilayer). Each such molecule has two parts - a head and a tail. The tails are hydrophobic and face each other. The heads, on the other hand, are hydrophilic Ο w S * s > s o X l s t- X t- OUTER layer INTERMEDIATE layer INTERNAL layer 19 Fig. 6. Basic structures of an animal cell: 1 - agranular (smooth) endoplasmic reticulum; 2 - glycocalyx; 3 - plasmalemma; 4 - cortical layer of the cytoplasm; 2 + 3 + 4 = cell surface complex; 5 - pinocytic vesicles; b - mitochondria; 7 - intermediate filaments; 8 - secretory granules; 9 - secretion; 10 - Golgi complex; 11 - transport vesicles; 12 - lysosomes; 13 - phagosome; 14 - free ribosomes; 15 - polyribosome; 16 - granular endoplasmic reticulum; 17 - bordered vesicle; 18 - nucleolus; 19 - nuclear lamina; 20 - perinuclear space limited by the outer and inner membranes of the karyotheca; 21 - chromatin, 22 - pore complex, 23 - cell center, 24 - microtubule, 25 - peroxisome 20 Fig. 7. Structure of a biological membrane: 1 - external proteins; 2 - protein in the thickness of the membrane; 3 - internal proteins; 4 - integral (transmembrane) protein; 5 - phospholipids of the bilipid layer) L C J J and are directed outward and into the cell. Protein molecules are immersed in the bilipid layer (Fig. 7). On fig. 8 is a schematic representation of the phosphatidylcholine phospholipid molecule. One of the fatty acids is saturated, the other is unsaturated. Lipid molecules are capable of rapidly diffusing laterally within one monolayer and very rarely pass from one monolayer to another. CH CH Fig ι- Ch^ 8. Phosphatidylcholine phospholipid molecule: A - polar (hydrophilic) head: 1 - choline, 2 - phosphate, 3 - glycerol: B - non-polar (hydrophobic) tail: 4 - saturated fatty acid, 5 - unsaturated fatty acid, CH=CH - cis double bond 21 The bilipid layer behaves like a liquid with a significant surface tension. As a result, it forms closed cavities that do not collapse. Some proteins pass through the entire thickness of the membrane, so that one end of the molecule faces the space on one side of the membrane, the other on the other. They are called integral (transmembrane). Other proteins are located in such a way that only one end of the molecule faces the near-membrane space, while the other end lies in the inner or outer monolayer of the membrane. Such proteins are called internal or, respectively, external (sometimes both are called semi-integral). Some proteins (usually transported across the membrane and temporarily residing in it) may lie between the phospholipid layers. The ends of protein molecules facing the near-membrane space can bind to various substances located in this space. Therefore, integral proteins play an important role in the organization of transmembrane processes. Semi-integral proteins are always associated with molecules that carry out reactions to perceive signals from the environment (molecular receptors) or to transmit signals from the membrane to the environment. Many proteins have enzymatic properties. The bilayer is asymmetric: different lipids are located in each monolayer, glycolipids are found only in the outer monolayer so that their carbohydrate chains are directed outward. Cholesterol molecules in eukaryotic membranes lie in the inner half of the membrane facing the cytoplasm. Cytochromes are located in the outer monolayer, and ATP synthetases are located on the inner side of the membrane. Like lipids, proteins are also capable of lateral diffusion, but its rate is slower than that of lipid molecules. The transition from one monolayer to another is practically impossible. 22 Bacteriorhodopsin is a polypeptide chain consisting of 248 amino acid residues and a prosthetic group - a chromophore that absorbs light quanta and is covalently bound to lysine. Under the influence of a light quantum, the chromophore is excited, which leads to conformational changes in the polypeptide chain. This causes the transfer of two protons from the cytoplasmic surface of the membrane to its outer surface, as a result of which an electric potential arises in the membrane, causing the synthesis of ATP. Among the membrane proteins of prokaryotes, permeases are distinguished - carriers, enzymes that carry out various synthetic processes, including the synthesis of ATP. The concentration of substances, in particular ions, is not the same on both sides of the membrane. Therefore, each side carries its own electrical charge. Differences in the concentration of ions create, respectively, the difference in electrical potentials. Surface complex The surface complex (Fig. 9) ensures the interaction of the cell with its environment. In this regard, it performs the following main functions: delimiting (barrier), transport, receptor (perception of signals from the environment external to the cell), as well as the function of transmitting information perceived by receptors to deep structures of the cytoplasm. The basis of the surface complex is a biological membrane, called the outer cell membrane (in other words, the plasmalemma). Its thickness is about 10 nm, so it is indistinguishable in a light microscope. The structure and role of biological membranes as such was discussed earlier, while the plasmalemma provides, first of all, a delimiting function in relation to the environment external to the cell. Naturally, it also performs other functions: transport and receptor (perception of signals from the external 23 1 Fig. 9. Surface complex: 1 - glycoproteins; 2 - peripheral proteins; 3 - hydrophilic heads of phospholipids; 4 - hydrophobic tails of phospholipids; 5 - microfilaments, 6 - microtubules, 7 - submembrane proteins, 8 - transmembrane (integral) protein (according to A. Ham and D. Cormack, with changes) for the cell medium). The plasma membrane thus provides the surface properties of the cell. The outer and inner electron-shut layers of the plasma membrane have a thickness of about 2-5 nm, the middle electron-transparent layer is about 3 nm. During freezing-cleavage, the membrane is divided into two layers: layer A, containing numerous, sometimes arranged in groups, large particles 8–9.5 nm in size, and layer B, containing approximately the same particles (but in a smaller amount) and small depressions. Layer A is a cleavage of the inner (cytoplasmic) half of the membrane, layer B is the outer. Protein molecules are immersed in the bilipid layer of the plasmalemma. Some of them (integral, or transmembrane) pass through the entire thickness of the membrane, others (peripheral or external) lie in the inner or outer monolayers of the membrane. Some integral proteins are linked by non-covalent bonds with cytoplasmic proteins. Like lipids, protein molecules are also amphipathic - their hydrophobic regions are surrounded by similar "tails" of lipids, while the hydrophilic ones face out or inside the cell. Proteins carry out most of the membrane functions: many of them are receptors, others are enzymes, and still others are carriers. Like lipids, proteins are also capable of lateral diffusion, but its rate is slower than that of lipid molecules. The transition of protein molecules from one monolayer to another is practically impossible. Since each monolayer contains its own proteins, the bilayer is asymmetric. Several protein molecules can form a channel through which certain ions or molecules pass. One of the most important functions of the plasma membrane is transport. Recall that the "tails" of lipids facing each other form a hydrophobic layer that prevents the penetration of polar water-soluble molecules. As a rule, the inner cytoplasmic surface of the plasma membrane carries a negative charge, which facilitates the penetration of positively charged ions into the cell. Small (18 Da) uncharged water molecules quickly diffuse through membranes; small polar molecules (for example, urea, CO2, glycerol), hydrophobic molecules (O2, N2, benzene) also quickly diffuse; large uncharged polar molecules are not able to diffuse at all (glucose, sucrose). At the same time, these substances diffuse easily through the cytolemma due to the presence in it of membrane transport proteins specific for each chemical compound. These proteins can function on the principle of uniport (transfer of one substance across the membrane) or cotransport (transfer of two substances). The latter can be in the form of a symport (transfer of two substances in one direction), 25 or an antiport (transfer of two substances in opposite directions) (Fig. 10). In transport, the second substance is H*. Uniport and symport are the main ways of transferring most of the substances necessary for its vital activity into the prokaryotic cell. There are two types of transport: passive and active. The first does not require energy, the second is volatile (Fig. 11). Passive transport of uncharged molecules is carried out along a concentration gradient, transport of charged molecules depends on the H+ concentration gradient and the transmembrane potential difference, which are combined into a transmembrane H+ gradient, or an electrochemical proton gradient (Fig. 12). As a rule, the inner cytoplasmic surface of the membrane carries a negative charge, which facilitates the penetration of positively charged ions into the cell. Diffusion (lat. diffusio - spreading, spreading) is the transition of ions or molecules caused by their Brownian movement through membranes from the zone 10. Scheme of functioning of transport proteins: 1 - transported molecule; 2 - cotransported molecule; 3 - lipid bilayer; 4 - carrier protein; 5 - antiport; 6 - symport; 7 - cotransport; 8 - uniport (according to B. Alberts et al.) 26 Extracellular space Pic. 11. Scheme of passive transport along the electrochemical gradient and active transport against the electrochemical gradient: 1 - transported molecule; 2 - channel-forming protein; 3 - carrier protein; 4 - electrochemical gradient; 5 - energy; 6 - active transport; 7 - passive transport (facilitated diffusion); 8 - diffusion mediated by a carrier protein; 9 - diffusion through the channel; 10 - simple diffusion; 11 - lipid bilayer (according to B. Alberts et al.) (++++++++ VI -ψ ^7 nht Fig. 12. Electrochemical proton gradient. Gradient components: 1 - inner mitochondrial membrane; 2 - matrix; 3 - proton motive force due to the membrane potential 4 - proton motive force due to the concentration gradient of protons (according to B. Alberts et al.) 27 where these substances are in a higher concentration, into a zone with a lower concentration until the both sides of the membrane will align.Diffusion can be neutral (uncharged substances pass between lipid molecules or through a channel-forming protein) or facilitated (specific carrier proteins bind the substance and carry it across the membrane).Facilitated diffusion is faster than neutral. Fig. 13 shows a hypothetical model of the functioning of carrier proteins during facilitated diffusion.Water enters the cell by osmosis (Greek osmos - push, pressure). The name mathematically proves the presence in the cytolemma of the smallest temporary pores that arise as needed. Active transport is carried out by carrier proteins, while energy is consumed due to the hydrolysis of ATP or proton potential. Active transport occurs against a concentration gradient. In the transport processes of a prokaryotic cell, the main role is played by the electrochemical proton gradient, while the transfer goes against the concentration gradient of substances. On the cytolemma of eukaryotic cells using a sodium-potassium pump 13. Scheme of the functioning of carrier proteins: 1 - transported substance; 2 - concentration gradient; 3 - transport protein that facilitates diffusion; 4 - lipid bilayer (according to B. Alberts et al.) 28 "*#" ν A ιίίϊίϊϊί Yag ADP+R ); 1 - sodium ion concentration gradient; 2 - potassium binding site; 3 - potassium ion concentration gradient; 4 - sodium binding site. During hydrolysis inside the cell of each ATP molecule, three Na ions are pumped out of the cell and two K * ions are pumped into the cell (according to B. Alberts et al.) the membrane potential is maintained. This pump, which functions as an antiport pumping K+ into the cell against concentration gradients and Na+ into the extracellular medium, is the ATPase enzyme (Fig. 14). At the same time, conformational changes occur in ATPase, as a result of which Na + is transferred through the membrane and excreted into the extracellular environment, and K + is transferred into the cell. The process resembles the facilitated diffusion model depicted in Fig. 13. ATPase also carries out active transport of amino acids and sugars. A similar mechanism is present in the cytolemma of aerobic bacteria. However, their enzyme, instead of hydrolyzing ATP, synthesizes it from ADP and phosphate using a proton gradient. The bacteriorhodopsin described above functions in the same way. In other words, the same enzyme carries out both the synthesis and hydrolysis of ATP. Due to the presence of a total negative charge in the cytoplasm of a prokaryotic cell, a number of 29 uncharged molecules are transferred according to the principle of symport with H*, the energy source is a transmembrane electrochemical gradient H+ (for example, glycine, galactose, glucose), negatively charged substances are transferred according to the principle of symport also with H* due to the Ht concentration gradient, Na+ transport is carried out according to the principle of antiport with H+, which is also transferred into the cell due to the H+ concentration gradient; the mechanism is similar to the NaT K+ pump in eukaryotes. Positively charged substances enter the cell according to the uniport principle due to the transmembrane difference in electrical potentials. The outer surface of the plasmalemma is covered with glycocalyx (Fig. 15). Its thickness is different and fluctuates even in different parts of the surface of one cell from 7.5 to 200 nm. The glycocalyx is a collection of molecules associated with membrane proteins. In composition, these molecules can be chains of polysaccharides, glycolipids, and glycoproteins. Many of the glycocalyx molecules function as specific molecular receptors. The terminal free section of the receptor has a unique spatial configuration. Therefore, only those molecules that are outside the cell can combine with it, 1 - glycocalyx, identified by a special dye (ruthenium red); 2 - ppaemapemma (part of the glycocalyx in this area is removed); 3 - cytoplasm; 4 - caroteca; 5 - chromatin (according to B. Alberts et al., with changes) 30 which also have a unique configuration, but mirror-symmetrical with respect to the receptor. It is due to the existence of specific receptors that the so-called signal molecules, in particular hormone molecules, can be fixed on the cell surface. The more specific specific receptors are in the glycocalyx, the more actively the cell reacts to the corresponding signal substances. If there are no molecules in the glycocalyx that specifically bind to external substances, the cell does not react to the latter. Thus, the glycocalyx, along with the plasmalemma itself, also provides the barrier function of the surface complex. Surface structures of the cytoplasm adjoin the deep surface of the plasmalemma. They bind to plasmalemma proteins and carry out the transfer of information to deep structures, triggering complex chains of biochemical reactions. They, changing their mutual position, change the configuration of the plasmalemma. Intercellular connections When cells come into contact with each other, their plasma membranes enter into interactions. In this case, special unifying structures are formed - intercellular connections (Fig. 16). They are formed during the formation of a multicellular organism during embryonic development and during the formation of tissues. Intercellular connections are divided into simple and complex. In simple junctions, the plasma membranes of adjacent cells form outgrowths like teeth, so that a tooth of one cell is embedded between two teeth of another (dentate junction) or intertwining interdigitations (finger-like junction). Between the plasmalemmas of neighboring cells, an intercellular gap of 15–20 nm in width is always preserved. ί 31 I II III Fig. 16. Intercellular connections: I - tight connection; II - desmosome; III - hemidesmosome; IV - nexus (gap-like connection); 1 - plasma membranes of adjacent cells; 2 - adhesion zones; 3 - electron-dense plates; 4 - intermediate filaments (tonofilaments) fixed in the plate; 5 - intercellular filaments; b - basement membrane; 7 - underlying connective tissue; 8 - connexons, each of which consists of 6 subunits with a cylindrical channel (according to A. Ham and D. Cormack and according to B. Alberts et al., with changes) 32 Complex connections, in turn, are divided into adhesive, closing and conductive. Adhesive junctions include desmosome, hemi-desmosome, and link band (ribbon-like desmosome). The desmosome consists of two electron-dense halves belonging to the plasma membranes of neighboring cells, separated by an intercellular space of about 25 nm in size, filled with a fine-fibrillar substance of a glycoprotein nature. Keratin tonofilaments, resembling head hairpins, are attached to the sides of both lamellae of the desmosome facing the cytoplasm. In addition, intercellular fibers connecting both plates pass through the intercellular space. The hemidesmosome, formed by only one plate with the tonofilaments included in it, attaches the cell to the basement membrane. The clutch belt, or ribbon-like desmosome, is a "ribbon" that goes around the entire surface of the cell near its apical section. The width of the intercellular space filled with fibrous substance does not exceed 15-20 nm. The cytoplasmic surface of the "tape" is compacted and strengthened by a contractile bundle of actin filaments. Tight junctions, or locking zones, pass through the apical surfaces of the cells in the form of belts 0.5–0.6 µm wide. There is practically no intercellular space and glycocalyx in tight contacts between the plasma membranes of neighboring cells. The protein molecules of both membranes are in contact with each other, so the molecules do not pass through tight contacts. On the plasmalemma of one cell there is a network of ridges formed by chains of elliptical protein particles located in the inner monolayer of the membrane, which correspond to grooves and grooves on the plasmalemma of the neighboring cell. Conductive connections include the nexus, or gap-like junction, and the synapse. Through them, water-soluble small molecules with a molecular weight of not more than 1500 Da pass from one cell to another. Many human (and animal) cells are connected by such contacts. In the nexus, between the plasma membranes of neighboring cells, there is a space 2–4 nm wide. Both plasmalemmas are interconnected by connexons - hollow hexagonal protein structures about 9 nm in size, each of which is formed by six protein subunits. The method of freezing and chipping showed that on the inner part of the membrane there are hexagonal particles 8–9 nm in size, and on the outer part there are corresponding pits. Gap junctions play an important role in the function of cells with pronounced electrical activity (for example, cardiomyocytes). Synapses play an important role in the implementation of the functions of the nervous system. Microvilli Microvilli provide an increase in cell surface. This, as a rule, is associated with the implementation of the function of absorption of substances from the environment external to the cell. Microvilli (Fig. 17) are derivatives of the surface complex of the cell. They are protrusions of the plasmalemma 1-2 µm long and up to 0.1 µm in diameter. In the hyaloplasm, there are longitudinal bundles of actin microfilaments; therefore, the length of the microvilli can change. This is one of the ways to regulate the activity of substances entering the cell. At the base of the microvillus in the surface complex of the cell, its microfilaments combine with elements of the cytoskeleton. The surface of microvilli is covered with glycocalyx. With a special activity of absorption, the microvilli are so close to each other that their glycocalyx merges. Such a complex is called a brush border. In the brush border, many glycocalyx molecules have enzymatic activity. 34 IV Fig. 17. Microvilli and stereocypy: I and II - microvilli; III and IV - stereocypy; I-III-schemes; IV - electron micrograph; 1 - hypocapix; 2 - pasmapemma; 3 - bundles of microfipaments (according to B. Apberts et al., with changes) Particularly large microvilli up to 7 microns in length are called stereocilia (see Fig. 17). They are present in some specialized cells (for example, in sensory cells in the organs of balance and hearing). Their role is not related to absorption, but to the fact that they can deviate from their original position. Such a change in the configuration of the cell surface causes its excitation, the latter is perceived by the nerve endings, and the signals enter the central nervous system. Stereocilia can be considered as special organelles that have evolved through the modification of microvilli. Biological membranes divide the cell into separate areas that have their own structural and functional features - compartments, and also delimit the cell from its environment. Accordingly, the membranes associated with these compartments have their own characteristic features. Ill 35 NUCLEUS A well-formed cell nucleus (Fig. 18) is present only in eukaryotes. Prokaryotes also have nuclear structures such as chromosomes, but they are not contained in a separate compartment. In most cells, the shape of the nucleus is spherical or ovoid, but there are nuclei of other shapes (annular, rod-shaped, spindle-shaped, bean-shaped, segmented, etc.). ). The sizes of the nuclei vary widely - from 3 to 25 microns. The ovum has the largest nucleus. Most human cells have a single nucleus, but there are two nuclei (for example, some neurons, liver cells, cardiomyocytes). Two-, and sometimes multi-nucleus, is associated with polyploidy (Greek polyploos - multiple, eidos - view). Polyploidy is an increase in the number of chromosome sets in the nuclei of cells. We take this opportunity to note that sometimes structures are called multinucleated cells that were formed not as a result of polyploidization of the original cell, but as a result of the fusion of several mononuclear cells. Such structures have a special name - symplasts; they are found, in particular, in the composition of skeletal striated muscle fibers. 10 Fig.18. Cell nucleus: 1 - outer membrane of the karyotheca (outer nuclear membrane); 2 - perinuclear - space; 3 - inner membrane "karyotheca (inner nuclear membrane); 4 - nuclear pamina; 4 5 - pore complex; 6 - ribosomes; 5 7 - nukpeoppasma (nuclear juice); 8 - chromatin; 9 - cistern of granular endoplasmic reticulum; 10 - nucleolus (according to B. Alberts et al., with modifications) 36 In eukaryotes, chromosomes are concentrated inside the nucleus and separated from the cytoplasm by the nuclear envelope, or karyotheca. The karyotheca is formed by the expansion and fusion of cisterns of the endoplasmic reticulum with each other. Therefore, the karyotheca is formed by two membranes - internal and external. The space between them is called the perinuclear space. It has a width of 20 - 50 nm and maintains communication with the cavities of the endoplasmic reticulum. From the side of the cytoplasm, the outer membrane is often covered with ribosomes. In some places, the inner and outer membranes of the karyoteka merge, and a pore forms at the fusion site. The pore does not gape: between its edges, protein molecules are ordered, so that a pore complex is formed as a whole. The pore complex (Fig. 19) is a complex structure that consists of two rows of 37 interconnected protein granules, each of which contains 8 granules located at an equal distance from each other on both sides of the nuclear envelope. These granules are larger than ribosomes. Granules located on the cytoplasmic side of the pore determine the osmiophilic material surrounding the pore. In the center of the opening of the pore, there is sometimes a large central granule associated with the granules described above (possibly, these are particles transported from the nucleus to the cytoplasm). The opening of the pore is closed by a thin diaphragm. Apparently, the pore complexes contain cylindrical channels about 9 nm in diameter and about 15 nm long. Through the pore complexes, selective transport of molecules and particles from the nucleus to the cytoplasm and vice versa is carried out. Pores can occupy up to 25% of the core surface. The number of pores in one nucleus reaches 3000 - 4000, and their density is about 11 per 1 μm2 of the nuclear envelope. Mostly different types of RNA are transported from the nucleus to the cytoplasm. All enzymes necessary for RNA synthesis come from the cytoplasm to the nucleus to regulate the intensity of these synthesis. In some cells, hormone molecules that also regulate the activity of RNA synthesis come from the cytoplasm to the nucleus. The inner surface of the karyoteca is associated with numerous intermediate filaments (see the Cytoskeleton section). Together, they form a thin plate here, called the nuclear lamina (Fig. 20 and 21). Chromosomes are attached to it. The nuclear lamina is associated with pore complexes and plays a major role in maintaining the shape of the nucleus. It is built from intermediate filaments of a special structure. The nucleoplasm is a colloid (usually in the form of a gel). Various molecules are transported along it, it contains a wide variety of enzymes, and RNA enters it from chromosomes. In living cells, it is outwardly homogeneous. 38 Fig. 20. Surface structures of the nucleus: 1 - inner nuclear membrane; 2 - integral proteins; 3 - nuclear lamina proteins; 4 - chromatin fibril (part of the chromosome) (according to B. Alberts et al., with changes) 21. The nucleus and perinuclear region of the cytoplasm: 1 - granular endoplasmic reticulum; 2 - pore complexes; 3 - inner nuclear membrane; 4 - outer nuclear membrane; 5 - nuclear lamina and submembrane chromatin (according to B. Alberts et al., with changes) 39 In living cells, the nucleoplasm (karyoplasm) is outwardly homogeneous (except for the nucleolus). After fixation and processing of tissues for light or electron microscopy, two types of chromatin become visible in the karyoplasm (Greek chroma - paint): well-stained electron-dense heterochromatin formed by osmiophilic granules 10–15 nm in size and fibrillar structures about 5 nm thick, and light euchromatin. Heterochromatin is located mainly near the inner nuclear membrane, in contact with the nuclear plate and leaving free pores, and around the nucleolus. Euchromatin is found between clusters of heterochromatin. In fact, chromatin is a complex of substances that form chromosomes - DNA, protein and RNA in a ratio of 1: 1.3: 2. The basis of each chromosome is formed by DNA, the molecule of which has the form of a spiral. It is packed with various proteins, among which there are histone and non-histone proteins. As a result of the association of DNA with proteins, deoxynucleoproteins (DNPs) are formed. Chromosomes and nucleoli In the chromosome (Fig. 22) the DNA molecule (see Fig. 4 and 5) is packed compactly. Thus, information stored in a sequence of 1 million nucleotides in a linear arrangement would occupy a segment 0.34 mm long. As a result of compaction, it occupies a volume of 1015 cm3. The length of one human chromosome in an extended form is about 5 cm, the length of all chromosomes is about 170 cm, and their mass is 6 x 10~12 g. DNA is associated with histone proteins, resulting in the formation of nucleosomes, which are the structural units of chromatin. Nucleosomes, resembling beads with a diameter of 10 nm, consist of 8 histone molecules (two molecules of histones H2A, H2B, H3 and H4 each), around which a DNA segment is twisted, including 40 dams»» Fig. 22. Levels of DNA packaging in the chromosome: I - nucleosomal thread: 1 - histone H1; 2-DNA; 3 - away from histones; II - chromatin fibril; III - a series of loop domains; IV - condensed chromatin in the loop domain; V - metaphase chromosome: 4 - microtubules of the achromatin spindle (kinetochore); 5 - kinetochore; 6 - centromere; 7 - chromatids (according to B. Apberts et al., with changes and additions) 41,146 base pairs. Between the nucleosomes there are linker regions of DNA consisting of 60 base pairs, and histone HI provides mutual contact between adjacent nucleosomes. Nucleosomes are only the first level of DNA folding. Chromatin is presented in the form of fibrils about 30 nm thick, which form loops about 0.4 μm long each, containing from 20,000 to 30,000 base pairs, which, in turn, are further compacted, so that the metaphase chromosome has an average size. 5 x 1.4 µm. As a result of supercoiling, DNPs in the dividing nucleus of chromosomes (Greek chroma - paint, soma - body) become visible when magnified with a light microscope. Each chromosome is made up of one long DNP molecule. They are elongated rod-shaped structures with two arms separated by a centromere. Depending on its location and the relative position of the arms, three types of chromosomes are distinguished: metacentric, having approximately the same arms; acrocentric, having one very short and one long arm; submetacentric, which have one long and one shorter arm. Some acrocentric chromosomes have satellites (satellites) - small sections of the short arm connected to it by a thin non-staining fragment (secondary constriction). The chromosome contains eu- and heterochromatic regions. The latter in the non-dividing nucleus (outside mitosis) remain compact. The alternation of eu- and heterochromatic regions is used to identify chromosomes. The metaphase chromosome consists of two sister chromatids connected by a centromere, each of which contains one DNP molecule, stacked in the form of a supercoil. During spiralization, the sections of eu- and heterochromatin fit in a regular way, so that alternating transverse bands are formed along the length of the chromatids. They are identified using 42 special colors. The surface of chromosomes is covered with various molecules, mainly ribonucleoproteins (RNPs). Somatic cells have two copies of each chromosome, they are called homologous. They are the same in length, shape, structure, arrangement of stripes, they carry the same genes that are localized in the same way. Homologous chromosomes can differ in the alleles of the genes they contain. A gene is a section of a DNA molecule on which an active RNA molecule is synthesized (see the "Protein Synthesis" section). The genes that make up human chromosomes can contain up to two million base pairs. So, chromosomes are double strands of DNA surrounded by a complex system of proteins. Histones are associated with some sections of DNA. They can cover them or release them. In the first case, this region of the chromosome is not capable of synthesizing RNA, while in the second case, synthesis occurs. This is one of the ways to regulate the functional activity of the cell by derepression and repression of genes. There are other ways to do this as well. Some sections of chromosomes remain surrounded by proteins constantly and in a given cell they never participate in RNA synthesis. They can be called blocked. Blocking mechanisms are varied. Typically, such regions are highly helical and covered not only by histones, but also by other proteins with larger molecules. Despiralized active regions of chromosomes are not visible under a microscope. Only a weak homogeneous basophilia of the nucleoplasm indicates the presence of DNA; they can also be detected by histochemical methods. Such areas are referred to as euchromatin. Inactive highly helical complexes of DNA and high molecular weight proteins stand out when stained in the form of clumps of heterochromatin. Chromosomes are fixed on the inner surface of the karyotheca to the nuclear lamina. 43 In general, chromosomes in a functioning cell provide the synthesis of RNA necessary for the subsequent synthesis of proteins. In this case, the reading of genetic information is carried out - its transcription. Not the entire chromosome is directly involved in it. Different parts of the chromosomes provide the synthesis of different RNA. Particularly distinguished are the sites synthesizing ribosomal RNA (rRNA); not all chromosomes have them. These sites are called nucleolar organizers. The nucleolar organizers form loops. The tops of the loops of different chromosomes gravitate towards each other and meet together. Thus, the structure of the nucleus, called the nucleolus, is formed (Fig. 23). It has three components. The weakly stained component corresponds to chromosome loops, the fibrillar component corresponds to transcribed rRNA, and the globular component corresponds to ribosome precursors. The nucleoli are also visible under a light microscope. Depending on the functional activity of the cell, either smaller or larger regions of organizers are included in the formation of the nucleolus. Sometimes their grouping can take place not in one, but in several places. Rice. 23. The structure of the nucleolus: I - scheme: 1 - karyotheca; 2 - nuclear lamina; 3 - nucleolar organizers of chromosomes; 4 - ends of chromosomes associated with the nuclear lamina; II - nucleolus in the cell nucleus (electron microscope photograph) (according to B. Alberts et al., with changes) 44 In these cases, several nucleoli are found in the cell. Areas in which nucleolar organizers are active are detected not only at the electron-microscopic level, but also by light-optics during special processing of preparations (special methods of silver impregnation). From the nucleolus, ribosome precursors move to the pore complexes. During the passage of the pores, further formation of ribosomes occurs. Chromosomes are the leading components of the cell in the regulation of all metabolic processes: any metabolic reactions are possible only with the participation of enzymes, while enzymes are always proteins, proteins are synthesized only with the participation of RNA. At the same time, chromosomes are also the guardians of the hereditary properties of the organism. It is the sequence of nucleotides in DNA chains that determines the genetic code. The totality of all genetic information stored in chromosomes is called the genome. When preparing a cell for division, the genome is doubled, and during the division itself, it is equally distributed between daughter cells. All problems related to the organization of the genome and the patterns of transmission of hereditary information are presented in the course of genetics. Karyotype The metaphase nucleus can be isolated from the cell, the chromosomes can be moved apart, counted and their shape studied. Cells of individuals of each biological species have the same number of chromosomes. Each chromosome during metaphase has its own structural features. The totality of these features is designated by the concept of "karyotype" (Fig. 24). Knowledge of the normal karyotype is necessary to detect possible deviations. Such deviations always serve as a source of hereditary diseases. 45 1 /φ(ϊ w it) The normal karyotype (set of chromosomes) (gray, kaguop - nut kernel, typos - sample) of a person includes 22 pairs of autosomes and one pair of sex chromosomes (either XX for women, or XY for men) In 1949, M. Barr discovered special dense bodies in the nuclei of cat neurons, which were absent in males.These bodies are also found in the interphase nuclei of other somatic cells of females.They were called bodies of sex chromatin (Barr bodies).In humans, they are have a diameter of about 1 µm and are best identified in neutrophilic segmented leukocytes, where they look like a "drumstick" associated with the nucleus. They are also well distinguishable in buccal mucosal epitheliocytes taken by scraping. Barr bodies represent one inactivated condensed X chromosome. lit PP G Y13 "14 f15 yi6 Wl7f18 I AO ί "* Χ19 Χ20 Λ21 Α22 Xx **ΐ- Fig. 24. Human karyotype (healthy male) (according to B. Albvrts et al. and V.P. Mikhailov, with changes) CYTOPLASMA Osn The main structures of the cytoplasm are hyaloplasm (matrix), organelles and inclusions. Hyaloplasm Physically and chemically, hyaloplasm (Greek hyalos - glass) is a colloid consisting of water, ions and many molecules of organic substances. The latter belong to all classes - to carbohydrates, and to lipids, and to proteins, as well as to complex compounds such as glycolipids, glycoproteins, and lipoproteins. Many of the proteins have enzymatic activity. A number of important biochemical reactions take place in the hyaloplasm, in particular, glycolysis is carried out - the phylogenetically most ancient process of energy release (Greek glykys - sweet and lysis - decay), as a result of which a six-carbon glucose molecule decomposes into two three-carbon molecules of pyruvic acid with the formation of ATP (see. section "Basic reactions of tissue metabolism"). The molecules of hyaloplasm, of course, interact with each other in a very orderly manner, but the nature of its spatial organization is still not clear enough. Therefore, we can only say in general terms that the hyaloplasm is structured at the molecular level. It is in the hyaloplasm that organelles and inclusions are suspended. Organelles Organelles are called elements of the cytoplasm, structured at the ultramicroscopic level and performing specific functions of the cell; organelles are involved in the implementation of those functions of the cell that are necessary to maintain its vital activity. This includes ensuring its energy metabolism, synthetic processes, ensuring the transport of substances, etc. Organelles inherent in all cells are called general-purpose organelles, while those inherent in some specialized types of cells are called special. Depending on whether the structure of the organelle includes a biological membrane or not, membrane and non-membrane organelles are distinguished. 47 General purpose organelles NON-MEMBRANE ORGANELLES.^III Non-membrane organelles include the cytoskeleton, cell center, and ribosomes. CYTOSKELETON The cytoskeleton (cellular skeleton), in turn, is formed by three components: microtubules, microfilaments, and intermediate filaments. Microtubules (Fig. 25) permeate the entire cytoplasm of the cell. Each of them is a hollow cylinder with a diameter of 20 - 30 nm. The microtubule wall has a thickness of 6-8 nm. It is formed by 13 threads (protofilaments) twisted in a spiral one above the other. Each thread, in turn, is made up of tubulin protein dimers. Each dimer is represented by a- and β-tubulin. The synthesis of tubulins occurs on the membranes of the granular endoplasmic reticulum, and the assembly in a spiral takes place in the cell center. Accordingly, many microtubules have a radial direction with respect to centrioles. From here they spread throughout the cytoplasm. Some of them are 2-z-R and s. 2 5. Microtubule structure: ■ tubulin subunits; associated proteins; moving particles 48 are located under the plasmalemma, where they, together with bundles of microfilaments, participate in the formation of the terminal network. Microtubules are strong and form the supporting structures of the cytoskeleton. Part of the microtubules is located in accordance with the forces of compression and tension experienced by the cell. This is especially noticeable in the cells of epithelial tissues, which delimit different environments of the body. Microtubules are involved in the transport of substances within the cell. Protein molecules in the form of short chains are connected (associated) with the microtubule wall at one of their ends in the form of short chains, which are capable of changing their spatial configuration (protein conformation) under appropriate conditions. In the neutral position, the chain lies parallel to the wall surface. In this case, the free end of the chain can bind to particles that are in the surrounding glycocalyx. After binding the particle, the protein changes its configuration and deviates from the wall, thereby moving the blocked particle along with it. The deflected chain passes the particle to the one hanging above it, which also deflects and passes the particle further. Due to the presence of conformable outer chains, microtubules provide the main flows of intracellular active transport. The structure of the microtubule wall can change under various influences on them. In such cases, intracellular transport may be impaired. Among the blockers of microtubules and, accordingly, intracellular transport is, in particular, the alkaloid colchicine. Intermediate filaments 8-10 nm thick are represented in the cell by long protein molecules. They are thinner than microtubules, but thicker than microfilaments, for which they got their name (Fig. 26). Intermediate filament proteins belong to four main groups. Some of their characteristics are given in table. 5. Each group, in its own 49 ^Gb Fig. 2 6. Intermediate filaments in the cell (according to K. de Duve, with changes) turn, includes several proteins (for example, more than 20 types of keratins are known). Each protein is an antigen, so an appropriate antibody can be created against it. If the antibody is labeled in some way (for example, by attaching a fluorescent label to it), then, by introducing it into the body, it is possible to detect the localization of this protein. Proteins of intermediate filaments retain their specificity even with significant changes in the cell, including its malignancy. Therefore, using specific labeled antibodies to intermediate filament proteins, it is possible to establish which cells were the primary source of the tumor. Microfilaments are protein filaments about 4 nm thick. Most of them are formed by molecules Types of intermediate filaments (according to B. Alberts et al.) (52) Glial fibrillar acidic protein (45) Neurofilament proteins (60, 100,130) Nuclear lamins A, B and C (65 - 75) Some structures in which these filaments occur Epithelial cells and their derivatives (hair, nails, etc.) Cells of mesenchymal origin Muscle cells Astrocytes and lemmocytes (Schwann cells) Neurons Nuclear lamina in all cells 50 Pic. 27. Actin microfilament: 1 - actin globules; 2 - tropomyosin; 3 - troponins (according to B. Albvrts et al., with changes) of actins, of which about 10 species have been identified. In addition, actin filaments can be grouped into bundles that form the proper supporting structures of the cytoskeleton. Actin in the cell exists in two forms: monomeric (globular actin) and polymerized (fibrillar actin). In addition to actin itself, other peptides can also take part in the construction of microfilaments: troponins and tropomyosin (Fig. 27). Polymeric actin filaments are able to form complexes with polymeric molecules of myosin protein. When myosin is present in the hyaloplasm as monomers, it does not enter into a complex with actin. The polymerization of myosin requires calcium ions. Its binding occurs with the participation of troponin C (by the name of the calcium element), its release - with the participation of troponin I (an inhibitory molecule), complexing with tropomyosin - with the participation of troponin T. After the actin-myosin complex arises, actin and myosin become capable of move longitudinally relative to each other. If the ends of the complex are fastened to some other intracellular structures, the latter approach each other. This underlies muscle contraction. There are especially many microfilaments in the area of ​​the cytoplasm related to the surface complex. Being connected to the plasmalemma, they are able to change its configuration. This is important for ensuring the entry of substances into the cell through pinocytosis and phagocytosis. The same mechanism is used by the cell 51 in the formation of outgrowths of its surface - lamellopod- (y. The cell can be fixed by the lamellopodia to the surrounding substrate and move to a new place. CELL CENTER The cell center (Fig. 28) is formed by two centrioles (diplosome) and centrosphere. The organelle got its name due to the fact that it is usually located in the deep sections of the cytoplasm, often near the nucleus or near the emerging surface of the Golgi complex.Both centrioles of the diplosome are located at an angle to each other.The main function of the cell center is the assembly of microtubules.Fig.28.Cell center : 1 - triplets of microtubules; 2 - radial spokes; 3 - the central structure of the "cart wheel"; 4 - satellite; 5 - lysosome; 6 - dictyosomes of the Golgi complex; 7 - bordered vesicle; 8 - cistern of granular endoplasmic reticulum; 9 - cisterns and tubules of the agranular endoppasmatic network; 10 - mitochondrion; 11 - residual body; 12 - microtubules; 13 - karyoteka (according to R. Krstic, with changes) Each centriole is a cylinder, the wall of which, in turn, consists of nine complexes of microtubules about 0.5 µm long and about 0.25 µm in diameter. Each complex consists of three microtubules and is therefore called a triplet. The triplets, located relative to each other at an angle of about 50°, consist of three microtubules (from inside to outside): complete A and incomplete B and C, each with a diameter of about 20 nm. Two handles extend from tube A. One of them is directed to the tube C of the neighboring triplet, the other is directed to the center of the cylinder, where the inner handles form the shape of a star or wheel spokes. Each microtubule has a typical structure (see earlier). The centrioles are mutually perpendicular. One of them rests with its end against the side surface of the other. The first is called the child, the second is the parent. The daughter centriole arises from the doubling of the mother centriole. The maternal centriole is surrounded by an electron-dense rim formed by spherical satellites connected by a dense material to the outer side of each triplet. The middle part of the maternal centriole may also be surrounded by a complex of fibrillar structures called a halo. Triplets of microtubules are united at the base of the maternal centriole by electron-dense clusters - roots (appendages). Towards the end of the satellites and to the halo region, tubulins are transported through the cytoplasm, and it is here that the assembly of microtubules occurs. Once assembled, they are separated and sent to different parts of the cytoplasm to take their place in the structures of the cytoskeleton. It is possible that satellites are also a source of material for the formation of new centrioles during their replication. The region of hyaloplasm around the centrioles and satellite is called the centrosphere. Centrioles are self-regulating structures that double in the cell cycle (see Cell Cycle section). When doubling, at first both centrioles diverge, and a small centriole formed by nine single microtubules appears perpendicular to the basal 53 end of the maternal one. Then two more are attached to each of them by self-assembly from tubulin. Centrioles are involved in the formation of the basal bodies of cilia and flagella and in the formation of the mitotic spindle. RIBOSOMES Ribosomes (Fig. 29) are bodies 20 x 30 nm in size (sedimentation constant 80). The ribosome consists of two subunits - large and small. Each subunit is a complex of ribosomal RNA (rRNA) with proteins. The large subunit (sedimentation constant 60) contains three different rRNA molecules associated with 40 protein molecules; the small one contains one rRNA molecule and 33 protein molecules. Synthesis of rRNA is carried out on chromosome loops - nucleolar organizers (in the region of the nucleolus). The assembly of ribosomes is carried out in the region of the pores of the karyotheca. The main function of ribosomes is to assemble protein molecules from amino acids delivered to them by transfer RNA (tRNA). Between the subunits of the ribosome there is a gap in which the messenger RNA (mRNA) molecule passes, and on the large subunit - Fig. 2 9. Ribosome: I - mapa subunit; II - larger subunit; III - association of subunits; upper and lower rows - images in different projections (according to B. Apberts et al., with changes) of the groove in which the emerging protein chain is located and along which it slides. Amino acids are assembled according to the sequence of nucleotides in the mRNA chain. In this way, the transmission of genetic information is carried out. Ribosomes can be found in the hyaloplasm singly or in groups in the form of rosettes, spirals, curls. Such groups are called polyribosomes (polysomes). Thus, an mRNA molecule can stretch over the surface of not only one, but several adjacent ribosomes. A significant part of the ribosomes is attached to membranes: to the surface of the endoplasmic reticulum and to the outer membrane of the karyotheca. Free ribosomes synthesize a protein necessary for the life of the cell itself, attached - a protein to be removed from the cell. The number of ribosomes in a cell can reach tens of millions. MEMBRANE ORGANELLES Each membrane organelle represents a structure of the cytoplasm bounded by a membrane. As a result, a space is formed inside it, delimited from the hyaloplasm. The cytoplasm is thus divided into separate compartments with their own properties - compartments (English compartment - compartment, compartment, compartment). The presence of compartments is one of the important features of eukaryotic cells. Membrane organelles include mitochondria, endoplasmic reticulum (ER), Golgi complex, lysosomes, and peroxisomes. Some authors also classify microvilli as common organelles. The latter are sometimes referred to as special organelles, but in fact they are found on the surface of any cell and will be described together with the surface complex of the cytoplasm. K. de Duve combined the EPS, the Golgi complex, lysosomes and peroxisomes with the concept of vacuum (see the section “Golgi complex”). 55 MITOCHONDRIA Mitochondria are involved in the processes of cellular respiration and convert the energy released in the process into a form available for use by other cell structures. Therefore, the figurative name "energy stations of the cell", which has become trivial, has been assigned to them. Mitochondria, unlike other organelles, have their own genetic system necessary for their self-reproduction and protein synthesis. They have their own DNA, RNA and ribosomes, which differ from those in the nucleus and other sections of the cytoplasm of their own cells. At the same time, mitochondrial DNA, RNA, and ribosomes are very similar to prokaryotic ones. This was the impetus for the development of the symbiotic hypothesis, according to which mitochondria (and chloroplasts) arose from symbiotic bacteria (L. Margulis, 1986). Mitochondrial DNA is circular (like bacteria) and makes up about 2% of a cell's DNA. Mitochondria (and chloroplasts) are able to multiply in the cell by binary fission. Thus, they are self-reproducing organelles. At the same time, the genetic information contained in their DNA does not provide them with all the proteins necessary for complete self-reproduction; some of these proteins are encoded by nuclear genes and enter the mitochondria from the hyaloplasm. Therefore, mitochondria in relation to their self-reproduction are called semi-autonomous structures. In humans and other mammals, the mitochondrial genome is inherited from the mother: during fertilization of the egg, the mitochondria of the sperm do not penetrate into it. Such a seemingly abstract, purely theoretical proposition has found a purely practical application in recent years: the study of the sequence of DNA components in mitochondria helps to reveal genealogical relationships along the female line. This can be essential 56 for the identification of a person. Historical and ethnographic comparisons were also interesting. So, in ancient Mongolian legends, it was stated that the three branches of this people descended from three mothers; studies of mitochondrial DNA have indeed confirmed that members of each branch have such special features that others do not. The main properties of mitochondria and the functions of their structural components are summarized in Table. 6. In a light microscope, mitochondria look like rounded, elongated or rod-shaped structures 0.3-5 µm long and 0.2-1 µm wide. Each mitochondrion is formed by two membranes - external and internal (Fig. 30). Table 6 Morphofunctional organization of mitochondria Structure Outer membrane Intermembrane space Inner membrane Submitochondrial particles Matrix Composition Approximately 20% of the total mitochondrial protein Enzymes of lipid metabolism Enzymes that use ATP to phosphorylate other nucleotides Respiratory chain enzymes, cytochromes, succinate dehydrogenase Transport proteins ATP synthetase Enzymes (except for succinate dehydrogenase) DNA, RNA, ribosomes, enzymes involved in the expression of the mitochondrial genome Function Transport Transformation of lipids into intermediate metabolites Phosphorylation of nucleotides Creation of an electrochemical proton gradient Transfer of metabolites into and out of the matrix Synthesis and hydrolysis of ATP Citric acid cycle, conversion of pyru- cotton wool, amino acids and fatty acids into acetylcoenzyme A Replication, transcription, translation 57 Between them there is an intermembrane space 10 - 20 nm wide. The outer membrane is even, while the inner one forms numerous cristae, which may look like folds and ridges. Sometimes cristae look like tubules with a diameter of 20 - 60 nm. This is observed in cells that synthesize steroids (here, mitochondria not only provide respiration processes, but also participate in the synthesis of these substances). Thanks to the cristae, the area of ​​​​the inner membrane increases significantly. The space bounded by the inner membrane is filled with colloidal mitochondrial matrix. It has a fine-grained structure and contains many different enzymes. The matrix also contains its own genetic apparatus of mitochondria (in plants, in addition to mitochondria, DNA is also contained in chloroplasts). From the side of the matrix, many electron-dense submitochondrial elementary particles (up to 4000 per 1 μm2 of the membrane) are attached to the surface of the cristae. Each of them has the shape of a mushroom (see Fig. 30). Rice. 30. Mitochondria: I - general structure scheme: 1 - outer membrane: 2 ~ inner membrane: 3 - cristae: 4 - matrix; II - diagram of the structure of the crista: 5 - fold of the inner membrane: 6 - mushroom bodies (according to B. Alberts et al. and C. de Duve, with changes) 58 Round head with a diameter of 9-10 nm through a thin stem with a diameter of 3-4 nm attached to the inner membrane. These particles contain ATPases - enzymes that directly provide for the synthesis and breakdown of ATP. These processes are inextricably linked with the tricarboxylic acid cycle (the citric acid cycle, or the Krebs cycle, see the section "Basic reactions of tissue metabolism"). The number, size and location of mitochondria depend on the function of the cell, in particular on its need for energy and on the place where energy is spent. So, in one hepatic cell their number reaches 2500. Many large mitochondria are contained in cardiomyocytes and myosymplasts of muscle fibers. In sperm, mitochondria rich in cristae surround the axoneme of the intermediate part of the flagellum. There are cells in which mitochondria are extremely large. Such a mitochondrion can branch and form a three-dimensional network. This is shown by reconstructing the cell structure from separate successive sections. On a flat section, only parts of this mitochondrion are visible, which creates the impression of their multiplicity (Fig. 31). Rice. 31. Giant mitochondria: Reconstruction from serial electron microscope photographs of muscle fiber sections (according to Yu. S. Chentsov, with changes) a compartment bounded by a membrane that forms many intussusceptions and folds (Fig. 32). Therefore, in electron microscopic photographs, the endoplasmic reticulum looks like many tubules, flat or rounded cisterns, membrane vesicles. On the membranes of the EPS, various primary synthesis of substances necessary for the life of the cell takes place. They can be conditionally called primary because the molecules of these substances will undergo further chemical transformations in other compartments of the cell. Rice. 32. Endoplasmic reticulum: 1 - tubules of a smooth (agranular) network; 2 - tanks of a granular network; 3 - outer nuclear membrane covered with ribosomes; 4 - pore complex; 5 - inner nuclear membrane (according to R. Kretin, with changes) 60 Most substances are synthesized on the outer surface of the EPS membranes. Then these substances are transported through the membrane into the compartment and there they are transported to the sites of further biochemical transformations, in particular to the Golgi complex. At the ends of the EPS tubules, they accumulate and then separate from them in the form of transport bubbles. Each vesicle is thus surrounded by a membrane and travels in the hyaloplasm to its destination. As always, microtubules take part in the transport. Among the products synthesized on EPS membranes, we especially note those substances that serve as a material for assembling cell membranes (the final assembly of membranes is carried out in the Golgi complex). There are two types of EPS: granular (granular, rough) and agranular (smooth). Both are the same structure. The outer side of the membrane of the granular ER, facing the hyaloplasm, is covered with ribosomes. Therefore, under light microscopy, the granular endoplasmic reticulum looks like a basophilic substance, giving a positive color for RNA. This is where protein synthesis takes place. In cells specialized in protein synthesis, the granular endoplasmic reticulum looks like parallel fenestrated (fenestrated) lamellar structures communicating with each other and with the perinuclear space, between which there are many free ribosomes. The surface of the smooth ER is devoid of ribosomes. The network itself is a set of small tubes with a diameter of about 50 nm each. Glycogen granules are often located between the tubules. In some cells, a smooth network forms a pronounced labyrinth (for example, in hepatocytes, in Leydig cells), in others - circular plates (for example, in oocytes). Carbohydrates and lipids are synthesized on the membranes of the smooth network, among them glycogen and cholesterol. 61 The smooth network is also involved in the synthesis of steroid hormones (in Leydig cells, in cortical endocrinocytes of the adrenal gland). Smooth ER is also involved in the release of chloride ions in the parietal cells of the epithelium of the gastric glands. Being a depot of calcium ions, the smooth endoplasmic reticulum is involved in the contraction of cardiomyocytes and skeletal muscle fibers. It also delimits future platelets in megakaryocytes. Its role is extremely important in the detoxification by hepatocytes of substances that come from the intestinal cavity through the portal vein into the hepatic capillaries. Through the lumens of the endoplasmic reticulum, the synthesized substances are transported to the Golgi complex (but the lumens of the network do not communicate with the lumens of the cisterns of the latter). Substances enter the Golgi complex in vesicles, which are first detached from the network, transported to the complex, and finally merge with it. From the Golgi complex, substances are also transported to their places of use in membrane vesicles. It should be emphasized that one of the most important functions of the endoplasmic reticulum is the synthesis of proteins and lipids for all cell organelles. GOLGI COMPLEX The Golgi complex (Golgi apparatus, intracellular reticular apparatus, CG) is a collection of cisterns, vesicles, plates, tubules, sacs. In a light microscope, it looks like a grid, but in reality it is a system of tanks, tubules and vacuoles. Most often, three membrane elements are detected in CG: flattened sacs (cistern), vesicles and vacuoles (Fig. 33). The main elements of the Golgi complex are dictyosomes (Greek dyction - network). Their number varies in different cells from one to several hundred. 62 Fig. 33. Various forms of the Golgi complex (according to B. Alberts et al. and according to R. Krstic, with changes) Dictyosomes are interconnected by channels. A single dictyosome is most often cup-shaped. It has a diameter of about 1 µm and contains 4–8 (average 6) flattened cisterns lying in parallel and permeated with pores. The ends of the tanks are widened. Bubbles and vacuoles are split off from them, surrounded by a membrane and containing various substances. Many membranous vesicles (including bordered ones) have a diameter of 50–65 nm. Larger secretory granules have a diameter of 66 to 100 nm. Some of the vacuoles contain hydrolytic enzymes, these are precursors of lysosomes. The widest flattened tanks face the EPS. Transport bubbles, carrying substances - products of primary syntheses, are attached to these tanks. Synthesis of polysaccharides continues in the cisterns, complexes of proteins, carbohydrates and lipids are formed, in other words, the brought macromolecules are modified. Here, the synthesis of polysaccharides, the modification of oligosaccharides, the formation of protein-carbohydrate complexes, and the covalent modification of transported macromolecules take place. As the substance is modified, it moves from one tank to another. Outgrowths appear on the side surfaces of the tanks, where substances move. The outgrowths split off in the form of vesicles, which move away from the CG in various directions along the hyaloplasm. The side of the CG, where substances from the EPS enter, is called the cis-pole (forming surface), the opposite side is called the trans-pole (mature surface). Thus, the Golgi complex is structurally and biochemically polarized. In the direction from the cis-pole to the trans-pole, the membrane thickness increases (from 6 to 8 nm), as well as the content of cholesterol and carbohydrate components in membrane glycoproteins. The activity of acid phosphatase, the activity of thiamine pyrophosphatase decreases in the direction from the emerging surface to the mature one. The last cistern of the transside and the bordered vesicles surrounding it contain acid phosphatase. This is especially interesting in connection with the question of the origin of lysosomes. The fate of the vesicles split off from the CG is different. Some of them go to the cell surface and remove the synthesized substances into the extracellular matrix. Some of these substances are metabolic products, while others are specially synthesized products with biological activity (secrets). Most often, in such cases, the vesicle membrane merges with the plasma membrane (there are other methods of secretion - see the section "Exocytosis"). In connection with this function, CG is often located on the side of the cell where substances are excreted. If it is carried out evenly from all sides, CG is represented by multiple dictyosomes interconnected by channels. 64 In the process of packing substances into bubbles, a significant amount of membrane material is consumed. It must be replenished. Membrane assembly is another function of the CG. This assembly is made from substances coming, as usual, from the EPS. Elements of membrane blocks are created in the cavities of dictyosomes, then embedded in their membranes, and finally separated with vesicles. The specific structure of the membrane depends on where it will be delivered and where it will be used. The membranes of the Golgi complex are formed and maintained by the granular endoplasmic reticulum - it is on it that membrane components are synthesized. These components are transported by transport vesicles budding from the intermediate zones of the network (transfusion) to the emerging surface of the dictyosome and fusing with it (cis-fusion). Vesicles are constantly budding from the trans side, and the membranes of the tanks are constantly being renewed. They supply the cell membrane, glycocalyx and synthesized substances to the plasma membrane. This ensures the renewal of the plasma membrane. The secretory pathway and membrane renewal are shown in Fig. 34. “Membranes never form de novo. They always arise from pre-existing membranes by adding additional constituents. Each generation transfers to the next, mainly through the egg, a stock of pre-formed (pre-existing) membranes, from which, directly or indirectly, all membranes of the body are formed by growth ”(K. de Duve, 1987). A. Novikov (1971) developed the concept of GERD (G - (complex) Golgi, ER - endoplasmic reticulum (network), L - lysosomes). GERL (Fig. 35) includes the last, mature dictyosome sac, irregularly shaped, with numerous thickenings (prosecretory granules, or condensing vacuoles), which, budding, turn into secretory 65 8 9 10 Fig. 34. Scheme of the secretory pathway and membrane renewal: 1 - the area where the synthesis of proteins takes place, intended for export from the cell; 2 - the area where the synthesis of proteins intended for membrane renewal occurs; 3 - area where glycoeylation occurs (1 + 2 + 3 - granular endoplasmic network); 4 - transport vesicles, where the formation of disulfide bridges occurs; 5 - Golgi complex, where the addition of lipids, sulfation, removal of side chains, terminal glycosylation occurs; b - prosecretory granule, where proteolytic refinement occurs; 7 - secretory granule, where the secretion is concentrated; 8 - plasmalemma; 9 - ecocytosis; 10 - embedding in the membrane; 11 - assembly of the membrane elements (according to K. de Duve, with changes) 66 Pic. 35. Scheme of the GERL complex (Golgi, Endoplasmic Reticulum, Lysosomes): 1 - tanks of the granular endoplasmic reticulum; 2 - transport bubbles; 3 - cis-cistern of the Golgi complex; 4 - lysosomes; 5 - connecting tubules; 6 - trans-cistern of the Golgi complex; 7 - condensation secretory vacuoles (according to R. Krstic, with changes) granules. Adjacent to it are the cisterns of the granular endoplasmic reticulum, devoid of ribosomes. There are channels between the GERL and the tank underneath. From GERD, which contains acid phosphatase, lysosomes, also containing this enzyme, bud off. It is possible that substances from the underlying cisterns of the Golgi complex and directly from the adjoining cisterns of the endoplasmic reticulum enter the GERL. R. Krstic (1976) pointed out the presence of direct channels between GERL and adjacent cisterns of the endoplasmic reticulum. In addition, elongated finger-like processes of the cisterns of the endoplasmic reticulum are introduced into the pores of the GERL. From GERL, finger-like processes extend, which are introduced into the pores of the penultimate cistern of the dictyosome. From what has been said, it is clear that in CG not only diverse syntheses are completed, but also a separation of the synthesized products takes place, sorting depending on their further destination. Such a 67 KG function is called segregation. One of the most important manifestations of the segregation function of the Golgi complex is the sorting of substances and their movement, which are carried out with the help of bordered vesicles. The main role in this process is played by membrane "address marks" - receptors that recognize specific markers according to the "lock - key" principle. For example, lysosomal enzymes are sorted in the Golgi complex by a membrane-bound receptor protein that “recognizes” mannose-6-phosphate, selects enzymes, and promotes their packaging into vesicles bordered by clathrin. The latter bud in the form of transport vesicles containing the indicated receptor in the membrane. Thus, they function as shuttles that deliver the mannose-6-phosphate receptor from the trans surface of the Golgi complex to the lysosomes and back; in other words, the receptor runs between strictly specialized membranes. As already noted, the Golgi complex is the main structure of the vacuome, it divides it into endoplasmic and exoplasmic domains and at the same time unites them functionally. The membranes of the endoplasmic domain differ from those of the exoplasmic domain. The latter are similar to the plasmalemma. Currently, the vacuome is called the vacuolar apparatus and includes, in addition to the Golgi complex and associated vacuoles, lysosomes and peroxisomes, also phagosomes with endosomes and the plasmalemma itself. Substances circulate in the cell, being packaged in membranes (movement of cell contents in containers, Fig. 36). The Golgi complex (namely GERL) is also the center of membrane circulation. At the same time, before the return of the membrane, which budded from the plasmalemma during endocytosis, the endosome is released from the substances transported into the cell. 68 Fig. 36. Scheme of movement of cell contents in containers ("shuttles"): A - endoplasmic domain; B - ekeoppasmatic domain; 1 - endoplasmic network; 2 - Golgi complex; 3 - plasmalemma; 4 - lieosomes; 5 - endosomes; b - “shuttle” of the Golgi lysosome through the plasmalemma and endosome; 7 - "shuttle" Golgi-plasmalemma; 7a - crinophagic deviation; 8a, 86 - pathways for the return of plasmalemma membranes; 8c - "shuttle" endosome-lysosome; 9 - autophagic segregation; 10 - "shuttle" llasmalemma-lysosome (bypassing the endosome); 11 - "shuttle" endosome-lysosome; 12 - "shuttle" of the laemalemma-endosome; 13 - direct "shuttle" of the Golgi lysosome; arrows with bright ends - the paths of movement (according to K. de Duve, with changes) The position of the Golgi complex in the cell is due to its functional specialization. In secreting cells, it is located between the nucleus and the excretion surface. So, in goblet cells, the nucleus is displaced to the basal end, and the Golgi complex is located between it and the apical surface. In the cells of the endocrine glands, from which the secret is excreted into the blood capillaries that surround the cell on all sides, the Golgi complex is represented by many superficially lying dictyosomes. In hepatocytes, dictyosomes 69 are located in groups: some near the biliary areas, others near the vascular ones. In plasma cells, when studied under a light microscope, the complex occupies a light zone near the nucleus; it is surrounded by a granular endoplasmic reticulum and looks like a “light courtyard” against its basophilic background. In all cases, mitochondria are concentrated near the Golgi complex. This is due to the energy-dependent reactions occurring in it. lysosomes Each lysosome (Fig. 37) is a membrane vesicle with a diameter of 0.4 - 0.5 microns. Its content is a homogeneous osmiophilic fine-grained material. It contains about 50 types of various hydrolytic enzymes in a deactivated state (proteases, lipases, phospholipases, nucleases, glycosidases, phosphatases, including acid phosphatase; the latter is a marker of lysosomes). The molecules of these enzymes, as always, are synthesized on the ribosomes of the granular ER, from where they are transported by transport vesicles to the CG, where they are modified. Primary lysosomes bud from the mature surface of the CG cisterns. All lysosomes of the cell form a lysosomal space, in which an acidic environment is constantly maintained with the help of a proton pump - pH ranges from 3.5-5.0. The membranes of lysosomes are resistant to the enzymes contained in them and protect the cytoplasm from their action. This is due to the special conformation of the molecules of the lysosomal membrane, in which their chemical bonds are hidden. Damage or violation of the permeability of the lysosomal membrane leads to the activation of enzymes and severe cell damage up to its death. The function of lysosomes is intracellular lysis (“digestion”) of macromolecular compounds 70 16 17 Pic. 37. Scheme of the structure and functioning of lysosomes (possible ways of forming secondary lysosomes by fusion of targets with primary lysosomes containing newly synthesized hydrolytic enzymes): 1 - phagocytosis; 2 - secondary lysosome; 3 - phagosome; 4 - residual body; 5 - multivesicular body; b - purification of lysosomes from monomers; 7 ~ pinocytosis; 8 - autophagosome; 9 - the beginning of autophagy; 10 - section of the agranular endoppasmatic network; 11 - granular endoplasmic reticulum; 12 - proton pump; 13 - primary lysosomes; 14 - Golgi complex; 15 - membrane recycling; 16 - plasmalemma; 17 - crinophagia; dotted arrows - directions of motion (according to K de Duve and B. Alberts et al., with modifications) 71 and particles. The latter can be own organelles and inclusions or particles that entered the cell from outside during endocytosis (see the section “Endocytosis”). The trapped particles are usually surrounded by a membrane. Such a complex is called a phagosome. The process of intracellular lysis is carried out in several stages. First, the primary lysosome fuses with the phagosome. Their complex is called the secondary lysosome (phagolysosome). In the secondary lysosome, enzymes are activated and break down the polymers that have entered the cell into monomers. This happens gradually, so secondary lysosomes are identified due to the presence of osmiophilic material of different electron density in them. Cleavage products are transported across the lysosomal membrane into the cytosol. Undigested substances remain in the lysosome and can remain in the cell for a very long time in the form of residual bodies surrounded by a membrane. Residual bodies are no longer classified as organelles, but as inclusions. Another way of transformation is also possible: the substances in the phagosome are completely cleaved, after which the phagosome membrane disintegrates. Fragments of membranes are sent to the CG and used in it to assemble new ones. Secondary lysosomes can fuse with each other, as well as with other primary lysosomes. In this case, peculiar secondary lysosomes are sometimes formed - multivesicular bodies. In the process of cell life at different hierarchical levels of its organization, starting from molecules and ending with organelles, structures are constantly being restructured. Near damaged or requiring replacement sections of the cytoplasm, usually in the vicinity of the Golgi complex, a semilunar double membrane is formed, which grows, surrounding the damaged zones on all sides (see Fig. 37). This structure then fuses with lysosomes. In such an autophagosome (autosome), organelle structures are lysed. 72 In other cases, during macro- or micro-autophagy, structures to be digested (eg, secretion granules) are invaginated into the lysosomal membrane, surrounded by it, and digested. An autophagic vacuole is formed. As a result of multiple microautophagy, multivesicular bodies are also formed (for example, in brain neurons and cardiomyocytes). Along with autophagy, some cells also undergo crinophagy (Greek krinein - to sift, separate) - the fusion of primary lysosomes with secretory granules. In the lysosomes of non-renewable cells, as a result of repeated autophagization, lipofuscin, the pigment of aging, accumulates. Thus, autophagy is one of the mechanisms for the renewal of intracellular structures - intracellular physiological regeneration. Autophagy eliminates organelles that have lost their activity in the process of their natural aging. Organelles that have become redundant are also eliminated if the intensity of physiological processes in the cell decreases during normal life. Autophagy is one of the ways to regulate functional activity. Since the changes in the latter are cyclic, autophagy is one of the mechanisms for the implementation of biological rhythms at the cellular level. In some cases, undigested residues accumulate in the lysosomes, leading to their overload (“chronic constipation”). The release of undigested residues by exocytosis and their accumulation in the extracellular environment can cause damage to extracellular structures. Therefore, this mechanism is rarely implemented. The most common three types of digestive disorders of the cell: intracellular release, extracellular release and overload (K. de Duve, 1987). 73 PEROXISOMS Peroxisomes (Fig. 38) are membranous vesicles with a diameter of 0.2 to 0.5 µm. Like lysosomes, they split off from the cisternae of the trans-pole of CG. There is also a point of view that peroxisome membranes are formed by budding from a smooth endoplasmic reticulum, and enzymes are synthesized by cytosol polyribosomes, from where they enter the peroxisome. Under the bubble membrane, a central denser part and a peripheral region are distinguished. There are two forms of peroxisomes. Small peroxisomes (0.15–0.25 μm in diameter) are present in almost all mammalian (and human) cells, contain fine-grained osmiophilic material, and morphologically differ little from primary lysosomes. Large peroxisomes (more than 0.25 μm in diameter) are present only in some tissues (liver, kidneys). They have a crystalline core, which contains enzymes in a concentrated form. Along with peroxisomes, there are other membrane microbodies with a diameter of 0.5 to 10 μm containing various enzymes. Rice. 3 8. Peroxisome: 1 - peroxisome membrane; 2 - crystalloid; 3 - inclusions of glycogen near the peroxisome (according to C. de Duve, with modifications) 74 Peroxisomes contain enzymes (peroxidase, catalase and D-amino acid oxidase). Peroxidase is involved in the exchange of peroxide compounds, in particular hydrogen peroxide, which is toxic to the cell. Molecular oxygen is used for biochemical reactions in peroxisomes. Peroxisomes are also involved in the neutralization of many other toxic compounds, such as ethanol. Catalase makes up about 40% of all proteins among peroxisome enzymes. Peroxisomes are also involved in the metabolism of lipids, cholesterol, and purines. Special organelles Recall that organelles are called special if only cells that perform special specialized functions have them. These are the brush border, stereocilia, basal labyrinth, cilia, kinetocillia, flagella, myofibrils. Among the special organelles in the infusion

The book is intended for students of schools with in-depth study of biology, applicants and students of higher educational institutions studying in areas and specialties in the field of medicine, biology, ecology, veterinary medicine, as well as for school teachers, graduate students and university professors.

Detailed modern data on the structure and vital activity of cells and tissues are presented, all cellular components are described. The main functions of cells are considered: metabolism, including respiration, synthetic processes, cell division (mitosis, meiosis). A comparative description of eukaryotic (animal and plant) and prokaryotic cells, as well as viruses, is given. Photosynthesis is considered in detail. Particular attention is paid to classical and modern genetics. The structure of tissues is described. A significant part of the book is devoted to the functional human anatomy.
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Detailed modern data on the structure and life of animals are presented. The most common groups of invertebrates and vertebrates are considered at all hierarchical levels - from ultrastructural to macroscopic. Particular attention is paid to the comparative anatomical aspects of various systematic groups of animals. A significant part of the book is devoted to mammals.
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Detailed modern data on the structure, life activity and taxonomy of plants, fungi, lichens and slime molds are presented. Particular attention is paid to plant tissues and organs, the structural features of organisms in a comparative aspect, as well as reproduction. Taking into account the latest scientific achievements, photosynthesis is described.
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For the first time, issues of the unified state exam (USE) are discussed and recommendations are given for preparing for it.
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Title: Biology for applicants to universities.

The guide presents modern data on the structure, functions and development of living organisms, their diversity, distribution on Earth, relationships with each other and with the environment. Problems of general biology (structure and function of eukaryotic and prokaryotic cells, viruses, tissues, genetics, evolution, ecology) are considered; functional human anatomy; morphology and taxonomy of plants, as well as fungi, lichens and slime molds; zoology of invertebrates and vertebrates.
For the first time, issues of the unified state exam (USE) are discussed and recommendations are given for preparing for it. The book is intended for schoolchildren and applicants entering universities in areas and specialties in the field of medicine, biology, ecology, veterinary medicine, agronomy, animal science, pedagogy, as well as for school teachers. Students can also use it with success.

Download and read Biology for university applicants. Bilich G.L., Kryzhanovsky V.A. 2008