Viruses form an independent kingdom (Vira) and have the following features:

The genome is represented by one nucleic acid - DNA or RNA (respectively, 2 sub-kingdoms are distinguished - riboviruses and deoxyriboviruses).

Non-cellular structure. Nucleic acid is coated with a protein coat - capsid, which consists of separate subunits - capsomers(usually consists of 5-6 polypeptides). The capsid together with nucleic acid forms nucleocapsid. Simple viruses have such a structure (poliomyelitis viruses, adenoviruses, etc.). Complex viruses have an outer envelope - supercapsid, which contains lipids, glycolipids. The supercapsid is partly formed by the host cell.

Lack of protein-synthesizing systems (in the presence of enzymes of adsorption, proliferation, DNA - and RNA - dependent polymerases).

A special (disjunctive) method of reproduction: the proteins of the virus are synthesized on the ribosomes of the affected cell, in other areas - the nucleic acid of the virus, then the viral particles are assembled.

Small size; small viruses (podiovirus, etc.) - 25-30 nm (nanometers); medium (influenza virus, etc.) - 50-125 nm; large (variola virus) - 150-200 nm.

7. Filterability (pass through bacterial filters).

8. Crystallization (extracellular viruses purified from ballast substances, virions, able to form crystals).

9. The form of virioi (distinguish rod-shaped - at rabies virus, etc., in the form of a polyhedron, icosahedron - in adenoviruses, cuboidal forms - in variola virus, spherical - in influenza viruses, capitate(sperm-like) - bacteriophages).

The cultivation of viruses also has its own peculiarities. They are cultivated on actively multiplying cells with increased metabolic activity. I use the following living systems. In the body of laboratory animals: usually infect mice (adults and suckers), rabbits, monkeys (intramuscularly, intranasally, intraperitoneally, intracerebrally, on the cornea). On 9-12-day-old chicken embryos: the dish is cultured on the embryo-allantoic membrane, less often in the allantoic or amniotic subnetwork. On cell culture: more often single-layer tissue culture from actively multiplying cells. Cells are grown on natural nutrient media (embryonic extracts, horse, human serum), enzymatic protein hydrolysates (tryptic hydrolyzate of lactalbumin), on synthetic media (for example, on medium 199, consisting of 63 components, including amino acids, vitamins, glucose, salts , human serum, an indicator of phenol red). The following types of cell cultures are used: primary trypsinized (usually chicken embryo fibroblasts; they are not intertwined and must always be prepared ex tempore; the disadvantage is that they are non-standard); transplanted (the same in all laboratories, since they are a specific clone of cells, for example, cells from portal tissues- human amnion, pig embryo kidney; cells from tumor tissues - HeLa (cervical cancer cells), HEp-2 and others; the disadvantage of this group is that cells often spontaneously degenerate, become atypical, polyploid, and are also spontaneously infected with latent viruses and mycoplasmas); semi-grafted diploid (for example, diploid cells of human lungs; they are stable, do not spontaneously regenerate, not contaminated with viruses and mycoplasmas).

There are the following forms of viral infections. Abortive infection (occurs in an unresponsive immune organism): the virus either does not enter the cell, or after penetration dies and is pushed out of the cell. Productive infection: the virus is adsorbed on sensitive cells and enters the cell by immersing its membrane with the virus inside, into the cytoplasm of the cell ( viro-rexis); in the formed phagosome, the nucleic acid of the virus is freed from the protein envelopes ("stripping the virus"); after the final undressing, the viral nucleic acid that has penetrated into the cell switches the functioning of the cellular genome and the corresponding metabolic systems of the cell for reproduction virus; the formed viral particles leave the cell and invade neighboring cells. Often this interaction ends in cell death, this process is referred to as cytopathicaction(CPD). An early sign of CPP is cessation of mitosis; the cell temporarily swells, then deforms, shrinks, becomes more intensely stained, exfoliates from glass (in cultures) and dies. Sometimes, before death, cells form symplasts(merged multinucleated cells). Virogeny: the viral nucleic acid that has penetrated into the cell integrates (integrates) into the DNA of the host cell (as in the case of a temperate phage) and in the form provirus exists in the cell and is passed on to its offspring. The phenomenon of virogeny is characteristic of both DNA and RNA viruses, since the latter have an enzyme reverse transcriptase(for example, retroviruses).

The modern classification of viruses is based on a number of features, including: the type of nucleic acid, the number of capsomeres, the presence of a supercapsid, sensitivity to ether, the range of susceptible hosts, pathogenicity, geographical distribution, etc.

Features of antiviral immunity. Immunity to viral infections may be due to the following factors. Factors of natural resistance: cellular unresponsiveness (as a result of phylogenesis, a person is immune to many viral diseases of animals and plants); inhibitors - substances of mucoprotein or lipoprotein nature, structurally identical to the receptors of sensitive cells (they circulate freely in the blood, other fluids and block the interaction of the virus with the cell); complement is involved in the formation of a specific (immune) antiviral response (lysozyme and other humoral factors do not play a protective role); phagocytosis is incomplete, but leukocytes, into which the virus has penetrated, produce interferon; interferon is synthesized by the cell after the penetration of the virus, it nonspecifically inhibits the reproduction of any viruses, disrupting the synthesis of viral proteins on ribosomes (only human interferon is active in the human body, which is produced by human leukocytes, or genetically engineered interferon - reaferon, produced by Escherichia coli, into the genome of which the human interferon gene has been introduced; interferon is widely used for the treatment and emergency prevention of viral infections); fever (high temperature interferes with the reproduction of viruses); the age factor (it matters, for example, with rotavirus infection, which children are more likely to get sick with); endocrine factors (hypofunction of many endocrine glands aggravates the course of viral infections); factors of the excretory system (contribute to the release of the body from viruses); the formation of intracellular inclusions may have a protective effect (Guarnieri's little body in case of smallpox, Babesha-Negri's little body in case of rabies).

The features of the acquired antiviral immunity in some cases determine persistent immunity (for example, after measles), in others - short-term (after rhinovirus infection). Antibodies act only on extracellularly located viruses (therefore, treatment with antiviral immunoglobulins is carried out early, until the bulk of the viruses have penetrated into the cells). Cells into which viruses have entered synthesize virus-dependent antigens and become foreign to the body, which leads to their destruction by killer T cells. The local resistance of cells is also important in defense reactions (for example, in a person refractory to poliomyelitis, cells of the nervous tissue and the gastrointestinal tract, to which the poliovirus has tropism, become resistant to the virus). Secretory immunoglobulins (slgA) are the main link of local immunity on the mucous membranes. Vaccination (with viral vaccines) creates not only specific immunity against an individual virus, but also forms resistance to other viruses (not only the production of antibodies and the formation of T-killers is stimulated, but also the production of interferon).

Viruses. Morphology and physiology of viruses

Minsk

LECTURE No. 8

TOPIC: ʼʼRNA - and DNA-containing viruses. HIV AIDS

Specialty - Nursing

Prepared by the teacher - Protko L.I.

Presentation outline:

3. HIV - AIDS. Epidemiology and pathogenesis. Prophylaxis

4. Influenza virus. Epidemiology and pathogenesis. Immunity, prevention

5. Viruses of hepatitis. Epidemiology and pathogenesis. Immunity, prevention

Viral diseases arose in ancient times, but virology as a science began to develop at the end of the 19th century.

In 1892ᴦ. Russian scientist-botanist D.I. Ivanovsky, studying mosaic disease of tobacco leaves, found that this disease is caused by the smallest microorganisms that pass through fine-pored bacterial filters. These microorganisms are called filterable viruses. Later it was shown that there are other microorganisms passing through bacterial filters, in connection with this, the filtered viruses began to be called simply viruses.

Virologists made a great contribution to the study of viruses: M.A. Morozov, N.F. Gamaleya, L.A. Zilber, M.P. Chumakov, A.A. Smorodintsev, V.M. Zhdanov and others.

Viruses are a non-cellular form of living matter. Οʜᴎ are very small. According to the figurative expression of V.M. Zhdanov “their size in relation to the size of average bacteria can be compared with the size of a mouse in relation to an elephant”. It became possible to see viruses only after the invention of the electron microscope.

Today, many methods are used to study viruses: chemical, physical, molecular biological, immunobiological, and genetic.

All viruses are subdivided into infecting humans, animals, insects, bacteria and plants.

Viruses have a wide variety of forms and biological properties, but they all have common structural features. Mature virus particles are called virions.

Unlike other microorganisms containing both DNA and RNA, the virion contains only one of the nucleic acids - either DNA or RNA.

The nucleic acid of viruses must be single-stranded and double-stranded. Almost all viruses containing RNA have single-stranded RNA in their genome, and those containing DNA have double-stranded DNA. In accordance with two types of genetic substance, viruses are divided into RNA- and DNA-containing. 6 families are DNA-containing, 11 families are RNA-containing.

Toxonamic sign	Family	Representatives
DNA-containing
2-stranded DNA, no outer sheath	Adenoviruses	Adenoviruses
Papoviruses	Human papilla, polynomial and warts virus
1-stranded DNA, no outer sheath	Parvoviruses	Adeno-associated viruses
2-stranded DNA, the presence of an outer shell	Herpesviruses	Herpes simplex virus, citalomegolia, chickenpox
Hepadnoviruses	Hepatitis B virus
Poxviruses	Smallpox virus, vaccinia
RNA containing
+ single-stranded RNA, no outer sheath	Picornoviruses	Poliomyelitis virus Coxsackie, ECHO, hepatitis A virus
Coliciviruses	Gastroenteritis virus in children
2-stranded RNA, no outer sheath	Reoviruses	Reoviruses, rotaviruses, orbiviruses
the presence of reverse transcriptase	Retroviruses	HIV, T-leukemia viruses, oncoviruses
+ single-stranded RNA, the presence of an outer shell	Togaviruses	Omsk hemorrhagic fever virus, rubella
+ single stranded RNA	Flaviviruses	Tick-borne encephalitis virus Dengue fever, yellow fever
-single stranded RNA	Bunyaviruses	Bunyamvera virus, Crimean hemorrhagic fever
Arenaviruses	Lymphocytic chormomeningitis viruses͵ Lasso disease
Rhabdoviruses	Rabies virus, vesicular stomatitis
2-stranded RNA, the presence of an outer sheath	Paramyxoviruses	Parainfluenza virus, paratitis measles, RSV
Orthomyxoviruses	Flu virus

The structure of the virion. In the center of the virion there is a nucleic acid, which is surrounded by a capsid. The capsid is made up of protein subunits called capsomeres. A mature virus is a nucleocapsid in chemical structure. The number of capsomeres and the way they are packed are strictly constant for each type of virus. Capsomeres are stacked in the form of a polyhedron with uniform symmetric edges - a cuboidal shape (adenovirus). Coiling is characteristic of influenza viruses. There may be a type of symmetry in which the nucleic acid has the form of a spring around which capsomeres are laid, in this case the virus has a rod-shaped form - a virus that causes tobacco leaf disease.

The phage has a complex type of symmetry: the head is cuboidal, and the process is rod-shaped.

Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, based on the method of detection, viruses are divided into cuboidal, spherical, rod-shaped and spermatozoid forms.

Some viruses with a more complex structure have a shell called peplos. It is formed when the virus leaves the host cell. In this case, the viral capsid is enveloped by the inner surface of the cytoplasmic membrane of the host cell and one or more layers of the supercapsid envelope are formed. Only some viruses have such a shell, for example, the viruses of rabies, herpes. This shell contains phospholipids, which are degraded by ether. Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, acting with ether, you can distinguish a virus with peplos from a virus with a "naked capsid".

In some viruses, capsomeres in the form of thorns (these thorns are blunt) protrude from the outer lipid layer of the envelope. These viruses are called peplomers (influenza virus).

The nucleic acid of the virus is the carrier of hereditary properties, and the capsid and the outer shell have protective functions, as if promoting the penetration of the virus into the cell.

The size of the viruses. Viruses are measured in nanoscale. Their magnitude fluctuates in a wide range from 15-20 to 350-400 nm.

Methods for measuring viruses.

1. Filtration through bacterial filters with a known spore size

2. Ultracentrifugation - large viruses sediment faster

3. Photographing viruses in an electron microscope

The chemical composition of viruses. The amount and content of DNA and RNA viruses are not the same. In DNA, the molecular weight ranges from 1‣‣‣10 6 to 1.6‣‣‣10 8, and in RNA, from 2‣‣‣10 6 to 9.0‣‣‣10 6.

Proteins in virions are found in an insignificant number. Οʜᴎ consist of 16-20 amino acids. In addition to capsid proteins, there are also internal proteins associated with nucleic acid. Proteins determine the antigenic properties of viruses, and also, due to the dense packing of polypeptide chains, protect the virus from the action of host cell enzymes.

Lipids and carbohydrates are found in the outer shell of complex virions. The host cell membrane is the source of lipids and carbohydrates. Polysaccharides, which are part of some viruses, determine their ability to cause agglutination of erythrocytes.

Virus enzymes. Viruses do not have their own metabolism; therefore, they do not need metabolic enzymes. At the same time, some viruses were found to have enzymes that facilitate their penetration into the host cell.

Identification of viral antigens. Viral antigens in infected host cells can be detected using immunofluorescence techniques. Preparations containing cells infected with viruses are treated with specific immune luminescent sera. When viewing the particles, a characteristic glow is observed. The type of virus is determined by the correspondence of the specific luminescent serum that caused the luminescence.

The introduction of the virus into the cell, its interaction with the host cell and reproduction(reproduction) are composed of a series of successive stages.

Stage 1. Begins with the process of adsorption at the expense of the virion and cell receptors. In complex virions, receptors are located on the surface of the membrane in the form of spine-like outgrowths, in simple virions - on the surface of the capsid.

Stage 2. Penetration of the virus into the host cell proceeds differently for different viruses. For example, some phages pierce the membrane with their sprout and inject nucleic acid into the host cell. Other viruses enter the cell by pulling in a viral particle using a vacuole, ᴛ.ᴇ. at the site of introduction in the cell membrane, a depression is formed, then its edges are closed and the virus appears in the cell. This retraction is commonly called viropexis.

Stage 3. "Stripping of the virus" (disintegration). It is important to note that for its reproduction, the viral nucleic acid is freed from the protein covers that protect it. The undressing process can begin during adsorption, or it can occur when the virus is already inside the cell.

Stage 4. At this stage, replication (reproduction) of nucleic acids and synthesis of viral proteins occurs. This stage occurs with the participation of the host cell's DNA or RNA.

Stage 5. Assembly of the virion. This process is facilitated by the self-assembly of protein particles around the viral nucleic acid. Protein synthesis can begin immediately after viral nucleic acid synthesis, or after an interval of several minutes or several hours. In some viruses, self-assembly occurs in the cytoplasm. Others have host cells in the nucleus. The formation of the outer shell always occurs in the cytoplasm.

Stage 6. The release of the virion from the host cell occurs by percolation of the virus through the cell membrane or through a hole formed in the host cell.

The types of interaction between the virus and the cell. The first type - productive infection - is characterized by the formation of new virions in the host cell

The second type - an abortive infection - essentially consists in the fact that the replication of the nucleic acid is interrupted.

The third type is characterized by the incorporation of viral nucleic acid into the DNA of the host cell; there is a form of coexistence of the virus and the host cell (virogeny). In this case, the synchronicity of viral and cellular DNA replication is ensured. In phages, this is commonly referred to as lysogeny.

Microscopic examination. With individual viral infections, specific intracellular bodies are observed in the cytoplasm or nuclei of the host's cells - inclusions that have diagnostic value. The sizes of viral particles and bodies-inclusions can be artificially increased by special methods of processing preparations with mordant and impregnation and observed with immersion microscopy. Smaller virions that lie outside the sight of an optical microscope are detected only with electron microscopy. There are different points of view regarding intracellular inclusions. Οʜᴎ the authors believe they are a collection of viruses. Others believe that they arise as a result of the cell's reaction to the introduction of viruses.

Genetics of viruses. Modification in viruses is due to the characteristics of the host cell in which the virus reproduces. The modified viruses acquire the ability to infect cells similar to those in which they were modified. The modification manifests itself differently in different viruses.

Mutation - in viruses, it occurs under the influence of the same mutagens that cause mutation in bacteria. A mutation occurs during nucleic acid replication. Mutations affect various properties of viruses, for example, sensitivity to temperature, etc.

Genetic recombination in viruses can result from the simultaneous infection of a host cell with two viruses, while individual genes can be exchanged between the two viruses and recombinants are formed containing the genes of the two parents.

Genetic reactivation of genes sometimes occurs when an inactivated virus is crossed with a complete one, which leads to the salvation of the inactivated virus.

Spontaneous and directed genetics of viruses are of great importance in the development of the infectious process.

Resistance to environmental factors. Most viruses are inactivated by exposure to high temperatures.
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However, there are exceptions, for example, the hepatitis virus is heat-resistant.

Viruses are not sensitive to low temperatures. Ultraviolet rays from the sun have an inactivating effect on viruses. Scattered sunlight acts on them less actively. Viruses are resistant to glycerol, which makes it possible to keep them in glycerol for a long time. Οʜᴎ antibiotic resistant.

Acids, alkalis, disinfectants inactivate viruses. At the same time, some viruses inactivated with formalin retain their immunogenic properties, which makes it possible to use formalin to obtain vaccines.

The susceptibility of animals. The range of susceptible animals for some viruses is very wide, for example, many animals are sensitive to rabies viruses. Some viruses only affect one species of animal, for example, the canine plague virus only affects dogs. There are viruses that animals are not sensitive to - the measles virus.

Organotropy of viruses. Viruses have the ability to infect certain organs, tissues and systems. For example, the rabies virus attacks the nervous system.

Release of viruses into the environment. From a sick body, viruses can be excreted in the feces, for example, the polio virus the rabies virus is excreted in saliva.

The main ways of transmission of viruses. Airborne, food, contact and household, transmission.

Antiviral immunity. The human body has an innate resistance to certain viruses. For example, a person is not susceptible to the canine plague virus.

Antiviral immunity is determined by both cellular and humoral defense factors, nonspecific and specific.

Non-specific factors. A powerful inhibitor of viral reproduction is a protein substance - interferon. In a healthy body, it is contained in an insignificant amount, and viruses contribute to the production of interferon and its amount increases significantly. It is nonspecific as it blocks the reproduction of various viruses. Moreover, it has tissue specificity, ᴛ.ᴇ. cells of different tissues form different interferon. It is believed that its mechanism of action essentially consists in the fact that it interferes with protein synthesis in the host cell and thereby stops the reproduction of the virus.

Specific factors of antiviral immunity include neutralizing antibodies, hemagglutinating and precipitating antibodies.

Basic methods of research of viruses.

1. Hemagglutination reaction, hemagglutination delay reaction, indirect hemagglutination reaction. Complement binding reaction

2. The reaction of neutralization of viruses in tissue culture

3. Method of immunofluorescence

4. Histological method - identification of inclusions

5. Biological method

Viruses. Morphology and physiology of viruses - concept and types. Classification and features of the category "Viruses. Morphology and physiology of viruses" 2017, 2018.

Rice. 4.1

The morphology of viruses is studied using electron microscopy, since their size is small (18-400 nm) and comparable to the thickness of the bacterial membrane. The form of virions can be different: rod-shaped (tobacco mosaic virus), bullet-shaped (rabies virus), spherical (poliomyelitis viruses, HIV), filamentous (filoviruses), in the form of a spermatozoon (many bacteriophages). Distinguish between simple and complex viruses (Table 4.1).

Just arranged viruses (no shell)

An example of simply arranged viruses is the hepatitis A virus and the papillomavirus with an icosahedral type of symmetry (Fig. 4.1 and 4.2). The nucleic acid of viruses is associated with a protein envelope - a capsid, consisting of capsomeres.

Rice. 4.2. Diagram of the structure of the papillomavirus (contains double-stranded circular DNA)

Complex viruses (with a shell)

In complex viruses (for example, herpes viruses, influenza, flaviviruses), glycoprotein spikes depart from the lipoprotein envelope, for example, hemagglutinins, which are involved in hemagglutination and hemadsorption reactions. The herpesvirus and flavivirus have an icosahedral symmetry, while the influenza virus has a helical nucleocapsid symmetry.

Table 4.1. Simple (without a shell) and complex (with a shell) viruses
Simple, or non-enveloped, viruses are composed of a nucleic acid and a protein coat called a capsid (from lat. capsa- case). The capsid consists of repeating morphological subunits - capsomeres. Nucleic acid and capsid interact with each other to form a nucleocapsid.	Symmetry type A capsid or nucleocapsid can be spiral, icosahedral (cubic), or complex symmetry. The icosahedral type of symmetry is due to the formation of an isometrically hollow body from a capsid,
Complex, or enveloped, viruses are surrounded by a lipoprotein membrane (supercapsid, or peplosome) outside the capsid. This envelope is a derived structure from the membranes of a virus-infected cell. On the envelope of the virus there are glycoprotein spines, or spines (peplomeres). Under the envelope of some viruses is the matrix M-protein.

Rice. 4.3.

Rice. 4.4.

Rice. 4.5

Rice. 4.6 .

Reproduction of viruses

There are three types of interaction between the virus and the cell:
- the productive type, in which new virions are formed that exit the cell in different ways: during its lysis, that is, by an "explosive" mechanism (non-enveloped viruses); by budding through cell membranes (enveloped viruses), as a result of exocytosis;
- the abortive type, characterized by the interruption of the infectious process in the cell, therefore, new virions are not formed;
- an integrative type, or virogeny, which consists in integration, i.e., the insertion of viral DNA in the form of a provirus into the cell chromosome and their coexistence (joint replication).
The productive type of interaction of the virus with the cell - the reproduction of the virus goes through several stages: 1) adsorption of virions on the cell; 2) penetration of the virus into the cell;
3) "undressing" and release of the viral genome (deproteinization of the virus); 4) synthesis of viral components;
5) the formation of viruses; 6) the release of virions from the cell.

Reproduction mechanism of viruses

The reproduction mechanism differs in viruses that have: 1) double-stranded DNA; 2) single-stranded DNA; 3) plus-single-stranded RNA; 4) minus single-stranded RNA; 5) double-stranded RNA;
6) identical plus-stranded RNA (retroviruses).
Double-stranded DNA viruses - viruses containing double-stranded DNA in a linear form (for example, herpes viruses, adenoviruses and poxviruses) or in a circular form (like papillomaviruses).
Replication of double-stranded viral DNA takes place by the usual semi-conservative mechanism: after unweaving the DNA strands, new strands are complementary to them. In all viruses, except for poxviruses, transcription of the viral genome occurs in the nucleus.
Reproduction of hepatnaviruses (hepatitis B virus) is unique in its mechanism.
The genome of hepadnaviruses (Fig. 4.7) is represented by double-stranded circular DNA, one strand of which is shorter (incomplete metatarsus) than the other. After penetration of the core of the virus into the cell (1) the incomplete strand of the DNA genome is completed; a complete double-stranded circular DNA (2) is formed and the maturing genome (3) enters the cell nucleus. Here, cellular DNA-dependent RNA polymerase synthesizes various mRNAs (for the synthesis of viral proteins) and RNA pregenome (4) - a template for replication of the viral genome. Then mRNA is transferred to the cytoplasm and translated to form virus proteins. The core proteins of the virus collect around the pregenome. Under the action of the RNA-dependent DNA polymerase of the virus, a minus-strand of DNA (5) is synthesized on the pregenome matrix, on which a plus-strand of DNA is formed (6). The virion membrane is formed on the HBs-containing membranes of the endoplasmic reticulum or the Golgi apparatus (7). The virion leaves the cell by exocytosis.

Rice. 4.7.

Single-stranded DNA viruses. Parvoviruses are representatives of single-stranded DNA viruses (Fig. 4.8).

The absorbed virus delivers the genome to the cell nucleus. Parvoviruses use cellular DNA polymerases to create a double-stranded viral genome, the so-called replicative form of the latter. At the same time, on the original viral DNA (plus-strand), a minus-DNA strand is complementary synthesized, which serves as a matrix in the synthesis of a plus-DNA strand for new generations of viruses. In parallel, mRNA is synthesized, translation of viral proteins occurs, which return to the nucleus, where virions are collected.
Plus single-stranded RNA viruses. This is a large group of viruses (picornaviruses, flaviviruses, togaviruses, etc.), in which the genomic RNA plus-strand performs the function of mRNA (Fig. 4.9).

The virus (1), after endocytosis, releases in the cytoplasm (2) genomic plus-RNA, which, like mRNA, binds to ribosomes (3): a polyprotein (4) is translated, which is cleaved into 4 structural proteins (NSP 1-4), including RNA -dependent RNA polymerase. This polymerase transcribes genomic plus-RNA into a minus-strand of RNA (template), on which (5) RNA copies of two sizes are synthesized: the full plus-strand of 49S genomic RNA; incomplete strand of 26S mRNA encoding C-capsid protein (6) and E1-3 envelope glycoproteins. Glycoproteins are synthesized on ribosomes associated with the membranes of the endoplasmic reticulum, then incorporated into the membrane and glycosylated. Additionally, glycosylated in the Golgi apparatus (7), they are incorporated into the plasmalemma. The C-protein forms a nucleocapsid with genomic RNA, which interacts with the modified plasmalemma (8). Viruses leave the cell by budding (9).
Minus single-stranded RNA viruses (rhabdoviruses, paramyxoviruses, orthomyxoviruses) contain an RNA-dependent RNA polymerase.
The genomic minus-strand of paramyxovirus RNA that has penetrated into the cell (Fig. 4.10) is transformed by viral RNA-dependent RNA polymerase into incomplete and complete plus-strands of RNA. Incomplete copies play the role of mRNA for the synthesis of viral proteins. Full copies are an intermediate matrix for the synthesis of minus strands of genomic RNA of offspring.

Figure 4.8.

Rice. 4.9.

Rice. 4.10

The virus binds to envelope glycoproteins with the cell surface and fuses with the plasmalemma (1). From the genomic minus RNA strand of the virus, incomplete plus RNA strands are transcribed, which are mRNA (2) for individual proteins and the complete minus RNA strand, a template for the synthesis of genomic minus RNA of the virus (3). The nucleocapsid binds to a matrix protein and a glycoprotein-modified plasmalemma. The release of virions is by budding (4).

Double-stranded RNA viruses... The reproduction mechanism of these viruses (reoviruses and rotaviruses) is similar to the reproduction of minus single-stranded RNA viruses.
The peculiarity of reproduction is that the plus strands formed during transcription function not only as mRNA, but also participate in replication: they are templates for the synthesis of minus RNA strands. The latter, in combination with RNA plus strands, form genomic double-stranded RNAs of virions. Replication of viral nucleic acids of these viruses occurs in the cytoplasm of cells.
Retroviruses (plus-strand diploid RNA viruses that reverse transcribed), such as human immunodeficiency virus (HIV).

HIV binds to the gp glycoprotein 120 (1) with receptorCD4 T-helpers and other cells. After shell merge

Rice. 4.11.

CPP - morphological changes in cells visible under a microscope (up to their rejection from glass) resulting from intracellular reproduction of viruses.
HIV with the cell plasmalemma in the cytoplasm releases genomic RNA and viral reverse transcriptase, which synthesizes a complementary minus DNA strand (linear cDNA) on the genomic RNA matrix. With the latter (2), the plus strand is copied to form a double strand of circular cDNA (3), which integrates with the chromosomal DNA of the cell. From the recombinant DNA provirus (4), genomic RNA and mRNA are synthesized, which provide the synthesis of components and the assembly of virions. Virions leave their cells by budding (5): the core of the virus "dresses" in the modified plasmalemma of the cell.

Cultivation and indication of viruses

Viruses are cultivated in the body of laboratory animals, in developing chicken embryos and in cell (tissue) cultures. Viruses are indicated on the basis of the following phenomena: cytopathogenic action (CPE) of viruses, formation of intracellular inclusions, plaque formation, hemagglutination reaction, hemadsorption or "color" reaction.

Rice. 4.13

Inclusions- the accumulation of virions or their individual components in the cytoplasm or cell nucleus, detected under a microscope with special staining. The variola virus forms cytoplasmic inclusions - Guarnieri's little bodies; herpes viruses and adenoviruses are intranuclear inclusions.

Rice. 4.14.

"Plaques" or "negative" colonies are limited areas of cells destroyed by viruses, cultured on a nutrient medium under an agar coating, visible as light spots against the background of stained living cells. One virion produces offspring in the form of one "plaque". "Negative" colonies of different viruses differ in size, shape, therefore, the "plaque" method is used to differentiate viruses, as well as to determine their concentration.

Rice. 4.12.

Figure 4.15.

The hemagglutination reaction is based on the ability of some viruses to cause agglutination (adhesion) of erythrocytes due to viral glycoprotein spikes - hemagglutinins.

The ability of cell cultures infected with viruses to adsorb erythrocytes on their surface.

Rice. 4.16.

The "color" reaction is assessed by the change in the color of the indicator in the culture medium. If viruses do not multiply in cell culture, then living cells in the process of metabolism release acidic products, which leads to a change in the pH of the medium and, accordingly, the color of the indicator. When viruses are produced, normal cell metabolism is disrupted (cells die), and the medium retains its original color.

- these are the smallest particles of life, they are 50 times smaller than bacteria. Usually viruses cannot be seen under a light microscope, since their specimens are more than half the length of the light wave. The dormant individuals of the virus are called virion. Viruses exist in two forms: resting, or extracellular (viral particles, or virions), and reproducing, or intracellular (complex "virus - host cell").

The forms of viruses are different, they can be threadlike, spherical, bullet-like, rod-shaped, polygonal, brick-like, cubic, while some have a cube-shaped head and a process. Each virion is composed of nucleic acid and proteins.

In virions of viruses, only one type of nucleic acid is always present - either RNA or DNA. Moreover, both the one and the other can be single-stranded and double-stranded, and DNA can be linear or circular. RNA in viruses is always only linear, but it can be represented by a set of RNA fragments, each of which carries a certain part of the genetic information necessary for reproduction. By the presence of one or another nucleic acid, viruses are called DNA-containing and RNA-containing. It should be especially noted that in the kingdom of viruses, the function of the guardian of the genetic code is performed not only by DNA, but also by RNA (it can also be double-stranded).

Viruses have a very simple structure... Each virus has only two parts - cores and capsid... The core of the virus, which contains DNA or RNA, is surrounded by a protein envelope - a capsid (lat. capsa- "container", "box", "case"). Proteins protect the nucleic acid, and also cause enzymatic processes and minor changes in proteins in the capsid. The capsid consists of one-type protein molecules arranged in a certain way - capsomers. Usually this is either a spiral type of laying (Fig. 22), or a type symmetric polyhedron(isometric type) (fig. 23).

All viruses are conventionally divided into simple and complex. Simple viruses consist only of a nucleic acid core and a capsid. Complex viruses on the surface of the protein capsid they also have an outer shell, or supercapsid, containing a bilayer lipoprotein membrane, carbohydrates and proteins (enzymes). This outer shell (supercapsid) is usually post-swollen from the membrane of the host cell. Material from the site

On the surface of the capsid there are various outgrowths - thorns, or "carnations" (they are called with fibers), and processes. With them, the virion attaches to the surface of the cell, into which it then penetrates. It should be noted that on the surface of the virus there are also special attachment proteins, binding the virion to specific groups of molecules - receptors(lat. recipio -"I receive", "I accept"), located on the surface of the cell into which the virus enters. Some viruses attach to protein receptors, others to lipids, while others recognize carbohydrate chains in proteins and lipids. In the process of evolution, viruses "learned" to recognize cells sensitive to them by the presence of special receptors on the cell surface of the hosts.