Viruses are the smallest of all microorganisms. They are measured in millimicrons and angstroms. Several methods are used to determine these particle sizes. So, a suspension of viruses is passed through special filters made of collodion, which have very small pores of a certain size. Filtration is carried out through several filters with different pore sizes. The difference between the pore diameters of the last filter that passed the virus particles and the filter that no longer passed the virus particles indicates the average size of the virus particles. With ultra-high-speed centrifugation (50 and more thousand revolutions per minute), the size of viral particles is determined by a special formula depending on the number of revolutions and the time of particles settling. In this case, the virus is also purified from foreign substances. For this, such speeds are selected at which foreign particles fall out, first large, and then the smallest. At the highest speed, only virus particles are obtained.

Man saw viruses only after 1940, when the electron microscope was built and improved. With an increase of tens and hundreds of thousands of times, it was possible to study the shape, size, and structure of the particles of some viruses.

It was found that both the size and shape of individual individuals (elementary particles) of different types of viruses are quite diverse. There are large viruses (for example, psittacosis, smallpox, trachoma, etc.), medium-sized viruses (influenza, plague, rabies) and small ones (polio, measles, foot-and-mouth disease, encephalitis, viruses of many plants). The table shows the sizes of some viruses, determined in different ways, in millimicrons (according to V. M. Zhdanov and Shen).

The largest viruses are close in size to the smallest bacteria, and the smallest viruses are close to large protein molecules.

In appearance, some viruses are spherical (influenza virus), others are cuboid (pox virus), and still others are bacillus-shaped. Tobacco mosaic virus (TMV) has the form of a thin hexagonal rod 300 mm long and 15 mm in diameter.

In many viral infections (smallpox, rabies, trachoma, etc.), special intracellular bodies, inclusions, specific for each infection, are observed in the cytoplasm or nucleus of the host cell. They are quite large and can be seen with a light microscope.

In most cases, inclusions are a cluster of elementary bodies, viral particles, as if their colony. Their presence in cells helps in the diagnosis of certain diseases.

One of the peculiar properties of many plant viruses is their ability to form crystals. D. I. Ivanovsky was the first to observe inclusions in tobacco leaves affected by TMV, now called Ivanovsky crystals. They consist of elementary particles of the tobacco mosaic virus. Virus crystals can be dissolved, as sugar and salt are dissolved. This virus can be isolated from solution in an amorphous, non-crystalline state. The precipitate can be re-dissolved, then again turned into crystals. If the crystal virus is dissolved a thousand times, then a drop of such a solution will cause a mosaic disease in the plant. So far, crystals of the poliomyelitis virus have been obtained from human and animal viruses. Each crystal is made up of millions of viral particles.

The chemical composition of viruses has been studied primarily in the causative agent of tobacco mosaic. This virus is a pure nucleoprotein, that is, it consists of protein and nucleic acid. The viral nucleoprotein of the tobacco mosaic has a huge molecular weight (40-50 million).

The virus particle has a complex structure. Nucleic acid is located inside the virus particle, it is surrounded by a protein shell. A virus particle usually contains one nucleic acid molecule.

Plant viruses contain ribonucleic acid, phages contain deoxyribonucleic acid. Human and animal viruses contain either RNA or DNA. RNA is found in influenza (1.6%), polio (24%), tobacco necrosis (18%), tobacco mosaic (6%), foot-and-mouth disease (40%), Rous sarcoma (10%) and other viruses. DNA is found in vaccinia viruses (6%), papilloma (6.8%), herpes (3.8%), polyoma (12%), etc.

Now the question of how protein and nucleic acid are connected, how they are fitted to each other, is being intensively studied. To resolve this issue, X-ray crystallography is used. If there are subunits in the virus particle, then this method can determine their number, as well as their relative position. It turned out that most viruses are characterized by a regular, highly ordered arrangement of the elements of the viral particle.

In the poliomyelitis virus, the nucleic acid is folded into a ball, the protein shell consists of 60 identical subunits, which are combined into 12 groups, 5 subunits each. The virus particle has a spherical shape.

The nucleic acid of the tobacco mosaic virus has the form of a spiral or spring. The protein shell of the TMV also consists of separate protein subunits of the same shape and size. There are 2200 subunits in total arranged in 130 turns around the nucleic acid rod. The molecular weight of such a subunit is 18,000. Each subunit is a peptide chain containing 158 specific amino acids, and the sequential arrangement of these amino acids has already been determined. Currently, the sequence of the 6500 nucleotides that form the nucleic acid is being intensively studied. When this problem is solved, then the plan will be known, which determines the type of virus that is formed in the infected cell. The structure, similar to the particles of TMV and poliomyelitis, have other small plant viruses.

In larger viruses, in addition to the nucleic acid, the protein shell, there are also outer shells containing proteins, lipoids, and carbohydrates. Some viruses contain enzymes. So, the influenza virus has the enzyme neuraminidase, the parainfluenza virus has sendai-lysin, the avian myeloblastosis virus contains adenovine triphosphatase. These enzymes dissolve the cell membrane to allow the virus to enter the body of its future host.

In a free state, in the external environment outside a living cell, viruses do not show activity, they only retain their viability, sometimes for a long time. But as soon as viruses meet cells that are sensitive to them, they become active, take root in them and show all signs of vital activity.

Previously, the only method of studying the vital activity of viruses was to infect experimental animals susceptible to them: mice, rabbits, monkeys, etc. It is more convenient and economical to grow viruses in a developing embryo of a chicken egg. The material containing the virus is injected with a syringe into the embryo on the 8-12th day of its development. After a few days of the embryo's stay in the thermostat, pathological changes caused by the virus in the embryo are studied. Then they are inoculated into a fresh embryo of another egg. Recently, the method of single-layer cultures from isolated cells of animal tissues has received the greatest use. Crushed fresh tissue is treated with the enzyme trypsin, which destroys intercellular bonds. The released cells are washed from trypsin, diluted with a nutrient composition (No. 199 containing the necessary amino acids and salts) and placed in test tubes or in special flat cups. In the thermostat, the cells multiply, forming a single-layer layer on the glass. Then this culture of homogeneous cells is infected with a virus and the processes occurring in it are studied under a microscope or by other means. So the laborious and expensive method, such as culture of the polio virus in the liver of monkeys, was replaced by a fast method of growing it in tissue culture.

In 1955 and later, unusual facts were obtained that caused bewilderment among biologists. Chemically, the tobacco mosaic virus was separated into its constituent parts: a protein and a nucleic acid. Each of them individually did not cause mosaic disease in tobacco leaves. But when they were put together again in a test tube (10 parts of protein and 1 part of nucleic acid) and infected tobacco leaves with this mixture, they got a typical mosaic on the leaves, as from the original whole TMV. Electron microscopy revealed typical virus rods, consisting of a protein coat in which a nucleic acid strand was enclosed. Thus, the nucleic acid bound to the protein part and took its normal position in it. The discovery of this phenomenon - virus reciprocity (recovery) - is the greatest achievement of modern microbiology, opening up new paths in biology and medicine.

Further, it turned out that it is enough to rub a leaf of tobacco with only one nucleic acid isolated from TMV in a mild way, as typical necroses appear on the leaf (of course, not in large quantities), in which there were a huge number of typical whole virus particles.

The same results were obtained with human viruses: poliomyelitis, influenza, etc.

Even a hybrid tobacco mosaic virus was obtained from the protein of one type of virus and the RNA of another type of virus, which differed in some respects from the first type virus. During reproduction, this hybrid virus produced offspring only of the virus whose RNA contained the hybrid.

All these facts indicate that nucleic acids play a leading role in the reproduction of viruses and their infectivity. Nucleic acids provide the transfer of hereditary properties. The acids contain hereditary information for the synthesis of full-fledged viral particles inside the cell.

The protein shell of the virus has a protective function, protecting the fragile strand of nucleic acid from external influences, in addition, it helps the virus to penetrate into the cell, determines the specificity of viruses. But some scientists do not consider it possible to limit the importance of proteins in this way. Further research is needed on the role of viral proteins.

The process of reproduction of viruses is fundamentally different from the process of reproduction of bacteria, protozoa and other cellular organisms.

Four phases of this process are distinguished: attachment of viral particles to the host cell, penetration of the virus into the cell, intracellular reproduction of the virus, and the release of new virus particles from the cell.

The first phase - attachment, or adsorption, of the virus to the cell - has been studied in relation to influenza and polio viruses. The cell wall has a mosaic structure, in some places mucoprotein molecules protrude, in others lipoprotein molecules. The influenza virus is adsorbed on mucoproteins, and the polio virus is adsorbed on lipoproteins. Adsorption can be observed with an electron microscope. At the site of adsorption of the virus, a recess is formed on the cell wall, where the virus particle is drawn. The edges of the recess close, and the virus particle is inside the cell (viropexis). Simultaneously with viropexis, the protein shell of the virus is destroyed. The penetration of the influenza virus into the cell is facilitated by the enzyme of its shell. Thus, nucleic acid, freed from protein shells, enters the cell with the help of the enzymes of the cell itself.

In the third phase, the viral nucleic acid that has entered the cell is included in the cell's metabolism and directs the cell's synthesis apparatus to produce protein and nucleic acid not of the cell, but of new viral particles. The activity of the enzymes involved in the synthesis of the virus is activated, and the other enzymes are inhibited. In addition, new enzymes are created that the cell did not have, but which are necessary for the synthesis of viral particles. It can be assumed that at this time a new unified virus-cell system is organized, switched to the synthesis of viral material. At the beginning of this phase, it is not possible to distinguish any elements of the virus in the cell.

Usually nucleic acids and proteins of the virus are synthesized not simultaneously and in different places of the cell. Nucleic acid synthesis begins first, followed by protein synthesis a little later. After the accumulation of these component parts of the virus, they are combined, assembled into full-fledged viral particles. Sometimes incomplete viral particles are formed, devoid of nucleic acid and therefore incapable of self-production (donuts).

The last phase quickly begins - the release of viral particles from the cell. In any place of the cell, about 100 particles of the virus immediately come out. More complex viruses also have outer shells of the viral nucleoprotein, with which they are enveloped during passage through the cell and exit from it, while the proteins of the host cell are part of the outer shells.

In human and animal viruses, the emergence of new offspring occurs in several cycles. So, in the influenza virus, each cycle lasts 5-6 hours with the release of 100 or more viral particles of one cell, and in total 5-6 cycles are observed within 30 hours. After that, the cell's ability to produce the virus is depleted, and it dies. The entire process of reproduction of the parainfluenza virus Sen Dai from adsorption to exit from the cell lasts 5-6 hours.

Sometimes virus particles do not leave the cell, but accumulate in it in the form of intracellular inclusions, which are very characteristic of different types of viruses. Plant viruses form inclusions having a crystalline form.

A family of microbes called "mycoplasma" is beginning to attract much attention, since recently pathogens of various human and animal diseases have been found in this group. In the form of a latent infection, they often live in many tissue cultures - Hela and others. Mycoplasmas occupy an intermediate position between bacteria and viruses. Filterability through bacterial filters brings them closer to viruses, filterable forms are capable of self-reproduction, intracellular reproduction. The features that bring viruses closer to bacteria include the ability to grow on nutrient media, to form colonies on them, as well as the attitude to antibiotics, sulfonamides and their antigenic structure.

Table of contents of the subject "Types of Microorganisms. Viruses. Virion.":
1. Microorganisms. Types of microorganisms. Classification of microorganisms. Prions.
2. Viruses. Virion. Morphology of viruses. Virus sizes. nucleic acids of viruses.
3. Capsid of the virus. Functions of the capsid of viruses. Capsomeres. Virus nucleocapsid. Helical symmetry of the nucleocapsid. Cubic symmetry of the capsid.
4. Virus supercapsid. Dressed up viruses. Naked viruses. Matrix proteins (M-proteins) of viruses. reproduction of viruses.
5. Interaction of a virus with a cell. The nature of the virus-cell interaction. Productive interaction. Virogeny. Virus interference.
6. Types of cell infection by viruses. The reproductive cycle of viruses. The main stages of the reproduction of viruses. Adsorption of the virion to the cell.
7. Penetration of the virus into the cell. Viropexis. Undressing the virus. Shadow phase (eclipse phase) of virus reproduction. The formation of viral particles.
8. Transcription of the virus in the cell. Translation of viruses.
9. Replication of the virus in the cell. Collection of viruses. Release of progeny virions from the cell.

Viruses. Virion. Morphology of viruses. Virus sizes. nucleic acids of viruses.

Extracellular form - virion- includes all constituent elements (capsid, nucleic acid, structural proteins, enzymes, etc.). Intracellular form - virus- can be represented by only one nucleic acid molecule, since, when it enters the cell, the virion breaks down into its constituent elements.

Morphology of viruses. Virus sizes.

Nucleic acids of viruses

Viruses contain only one type of nucleic acid, DIC or RNA, but not both types at the same time. For example, smallpox, herpes simplex, Epstein-Barr viruses are DNA-containing, and togaviruses, picornaviruses are RNA-containing. The genome of the viral particle is haploid. The simplest viral genome encodes 3-4 proteins, the most complex - more than 50 polypeptides. Nucleic acids are represented by single-stranded RNA molecules (excluding reoviruses, in which the genome is formed by two strands of RNA) or double-stranded DNA molecules (excluding parvoviruses, in which the genome is formed by one strand of DNA). In the hepatitis B virus, the strands of the double-stranded DNA molecule are unequal in length.

Viral DNA form circular, covalently linked supercoiled (for example, in papovaviruses) or linear double-stranded structures (for example, in herpes and adenoviruses). Their molecular weight is 10-100 times less than the mass of bacterial DNA. Transcription of viral DNA (mRNA synthesis) is carried out in the nucleus of a virus-infected cell. In viral DNA, at the ends of the molecule, there are direct or inverted (180" unfolded) repeating nucleotide sequences. Their presence ensures the ability of the DNA molecule to close into a ring. These sequences, present in single- and double-stranded DNA molecules, are a kind of viral DNA markers.

Rice. 2-1. Sizes and morphology of the main causative agents of human viral infections.

Viral RNA represented by single- or double-stranded molecules. Single-stranded molecules can be segmented - from 2 segments in arenaviruses to 11 segments in rotaviruses. The presence of segments leads to an increase in the coding capacity of the genome. Viral RNA subdivided into the following groups: plus strands of RNA (+RNA), minus strands of RNA (-RNA). In various viruses, the genome can form +RNA or -RNA strands, as well as double strands, one of which is -RNA, the other (complementary to it) - +RNA.

Plus-strand RNA are represented by single chains with characteristic endings (“caps”) for ribosome recognition. This group includes RNAs that can directly translate genetic information on the ribosomes of a virus-infected cell, that is, perform the functions of mRNA. Plus strands perform the following functions: they serve as mRNA for the synthesis of structural proteins, as a template for RNA replication, and they are packaged into a capsid to form a daughter population. RNA minus strands are unable to translate genetic information directly on ribosomes, meaning they cannot function as mRNA. However, such RNAs serve as templates for mRNA synthesis.

Infectivity of nucleic acids of viruses

Many viral nucleic acids are infectious in themselves, as they contain all the genetic information necessary for the synthesis of new viral particles. This information is realized after the penetration of the virion into the sensitive cell. Nucleic acids of most +RNA- and DNA-containing viruses exhibit infectious properties. Double-stranded RNAs and most RNAs are not infectious.

The scene of action is the laboratory of the Nikitsky Botanical Garden at the Russian Academy of Sciences, where the biologist Dmitry Iosifovich Ivanovsky (1864-1920) studies the mysterious mosaic disease of tobacco. The causative agent of the disease in a plant passes through the smallest bacterial filters, does not grow on and does not give symptoms when healthy plants are infected with filtrates from diseased ones.

It was then, in 1892, that the scientist concluded that it was not bacteria. And he calls the pathogen viruses (from the Latin virus, - poison). Dmitry Ivanovsky tried to see viruses all his life, but we saw the morphology of viruses in the 30s of the XX century, when electron microscopes were invented.

But it is this date that is considered the beginning of the science of virology, and Dmitry Ivanovsky is its founder.

amazing kingdom

The distinguishing features of viruses are as follows:

Part of the organic world of the planet

To date, more than 6,000 viruses have been described, but it is estimated that there are more than a hundred million. This is the most numerous biological form on the planet, and it is represented in all ecosystems (ubiquitous (ubiquitous) distribution).

Their appearance on the planet today is not clear. One thing is known - when the first cellular life forms appeared, viruses already existed.

Alive and not alive

These amazing organisms have two forms of their existence, which are significantly different from each other.

The virion is essentially an inanimate part of life. And the genome of the virus in the cell is its living component, because it is there that the reproduction of viruses occurs.

Morphology and ultrastructure of viruses

In this context, we are talking about a virion - an extracellular form.

The size of virions is measured in nanometers - 10 -9 meters. Influenza viruses are medium in size - 80-120 nanometers, and the smallpox virus is a giant with dimensions of 400 nanometers.

The structure and morphology of viruses is similar to astronauts. Inside the capsid (a protein shell, sometimes containing fats and carbohydrates), as in a "space suit", is the most valuable part - nucleic acids, the virus genome. Moreover, this “cosmonaut” is also represented in a minimal amount - only directly hereditary material and a minimum of enzymes for its replication (copying).

Outwardly, the "suit" can be rod-shaped, spherical, bullet-shaped, in the form of a complex icosahedron, or not at all regular in shape. It depends on the presence in the capsid of specific proteins that are responsible for the penetration of the virus into the cell.

How does the pathogen enter the host?

There are many ways of penetration, but the most common is airborne. Myriads of tiny particles are thrown into space not only when coughing or sneezing, but simply when breathing.

Another way for virions to enter the body is contagious (direct physical contact). This method is inherent in a fairly small group of pathogens, this is how herpes, sexually transmitted infections, AIDS are transmitted.

The method of infection through a carrier, which can be different groups of organisms, is quite complicated. A vector that has acquired a pathogen from a reservoir of infection becomes a site for viruses to replicate or progress through developmental stages. The rabies virus is just such a pathogen.

What happens in the host body

With the help of external proteins of the capsid, the virus attaches to the cell membrane and penetrates through endocytosis. They enter the lysosomes, where, under the action of enzymes, they get rid of the “space suit”. And the nucleic acids of the pathogen enter the nucleus or remain in the cytoplasm.

Nucleic acids of the pathogen are built into the chains of nucleic acids of the host, and the reaction of replication (copying) of hereditary information is launched. When a sufficient number of viral particles accumulate in the cell, the virions use the energy and plastic mechanisms and resources of the host.

The last stage is the release of virions from the cell. Some viruses lead to complete destruction of cells and enter the intercellular space, while others enter it through exocytosis or budding.

Pathogen strategies

The structure of the morphology of viruses leads to the complete dependence of the pathogen on the energy and protein-synthesizing potential of the cell, the only condition is that it replicates its nucleic acids according to its own schedule. Such an interaction is called productive (it is natural for a virus, but not for a cell). Having exhausted the supply of the cell, the virus leads to its death.

Another type of interaction is consensual. In this case, the virus genome, integrated into the host genome, replicates covalently with the cell's own nucleic acids. And then the development of the scenario can go in two directions. The virus behaves quietly and does not manifest itself. Young virions leave the cell only under certain conditions. Either the pathogen genes are constantly working, producing a large number of the young generation, but the cell does not die, but they leave it through exocytosis.

Complexities of taxonomy

The classification and morphology of viruses is different in various sources. The following features are used to classify them:

• The type of nucleic acid (RNA-containing and DNA-containing) and the method of its replication. The most common classification of viruses proposed by the American virologist David Baltimore in 1971.
• Morphology and structure of the virus (single-stranded, double-stranded, linear, circular, fragmented, not fragmented).
• Dimensions, type of symmetry, number of capsomeres.
• The presence of a supercapsid (outer shell).
• antigenic properties.
• Type of genetic interaction.
• Circle of potential hosts.
• Localization in the host cell - in the nucleus or in the cytoplasm.

It is the choice of the main criterion and the morphology of viruses that determines various approaches to the classification of viruses in microbiology. It's not quite easy. The difficulty lies in the fact that we begin to study the morphology and structure of the virus only when they lead to pathological processes.

Picky and not so picky

By host choice, these pathogens are extremely diverse in their preferences. Some attack only one biological species - they have a very strict "registration". For example, it eats flu viruses of cats, gulls, pigs, which are completely safe for other animals. Sometimes the specialization is surprising - the bacteriophage P-17 virus infects only males of one variety of Escherichia coli.

Other viruses behave quite differently. For example, bullet-shaped viruses, whose morphology is similar to a bullet, cause completely different diseases and, at the same time, their range of hosts is extremely wide. Such viruses include the rabies virus, which infects all mammals, or the vesicular stomatitis virus (transmitted, by the way, through insects).

Microbiology: lecture notes Tkachenko Ksenia Viktorovna

1. Morphology and structure of viruses

Viruses are microorganisms that make up the kingdom of Vira.

Features:

2) do not have their own protein-synthesizing and energy systems;

3) do not have a cellular organization;

4) have a disjunctive (separated) mode of reproduction (the synthesis of proteins and nucleic acids occurs in different places and at different times);

6) viruses pass through bacterial filters.

Viruses can exist in two forms: extracellular (virion) and intracellular (virus).

The shape of the virions can be:

1) rounded;

2) rod-shaped;

3) in the form of regular polygons;

4) filiform, etc.

Their sizes range from 15–18 to 300–400 nm.

In the center of the virion is a viral nucleic acid covered with a protein coat - a capsid, which has a strictly ordered structure. The capsid is made up of capsomeres. Nucleic acid and capsid make up the nucleocapsid.

The nucleocapsid of complexly organized virions is covered with an outer shell, the supercapsid, which can include many functionally different lipid, protein, and carbohydrate structures.

The structure of DNA and RNA viruses does not fundamentally differ from the NCs of other microorganisms. Some viruses have uracil in their DNA.

DNA can be:

1) double-stranded;

2) single-stranded;

3) ring;

4) double-stranded, but with one shorter chain;

5) double-stranded, but with one continuous and the other fragmented chains.

RNA can be:

1) single-strand;

2) linear double-strand;

3) linear fragmented;

4) ring;

Viral proteins are divided into:

1) genomic - nucleoproteins. Provide replication of viral nucleic acids and virus reproduction processes. These are enzymes, due to which the number of copies of the parent molecule increases, or proteins, with the help of which molecules are synthesized on the nucleic acid matrix that ensure the implementation of genetic information;

2) proteins of the capsid shell - simple proteins with the ability to self-assemble. They add up to geometrically regular structures, in which several types of symmetry are distinguished: spiral, cubic (form regular polygons, the number of faces is strictly constant) or mixed;

3) proteins of the supercapsid shell are complex proteins, diverse in function. Due to them, the interaction of viruses with a sensitive cell occurs. They perform protective and receptor functions.

Among the proteins of the supercapsid shell, there are:

a) anchor proteins (at one end they are located on the surface, while at the other they go into the depth; they provide contact of the virion with the cell);

b) enzymes (can destroy membranes);

c) hemagglutinins (cause hemagglutination);

d) elements of the host cell.

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Chapter 6

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Chapter 10 The world of viruses and its evolution Per. G. Janus Viruses were discovered as something completely unremarkable, namely an unusual variety of infectious agents, and possibly a special kind of toxins that cause plant diseases, such as tobacco mosaic. Since these agents

Viruses are microorganisms that make up the kingdom of Vira.

Features:

2) do not have their own protein-synthesizing and energy systems;

3) do not have a cellular organization;

4) have a disjunctive (separated) mode of reproduction (the synthesis of proteins and nucleic acids occurs in different places and at different times);

6) viruses pass through bacterial filters.

Viruses can exist in two forms: extracellular (virion) and intracellular (virus).

The shape of the virions can be:

1) rounded;

2) rod-shaped;

3) in the form of regular polygons;

4) filiform, etc.

Their sizes range from 15–18 to 300–400 nm.

In the center of the virion is a viral nucleic acid covered with a protein coat - a capsid, which has a strictly ordered structure. The capsid is made up of capsomeres. Nucleic acid and capsid make up the nucleocapsid.

The nucleocapsid of complexly organized virions is covered with an outer shell, the supercapsid, which can include many functionally different lipid, protein, and carbohydrate structures.

The structure of DNA and RNA viruses does not fundamentally differ from the NCs of other microorganisms. Some viruses have uracil in their DNA.

DNA can be:

1) double-stranded;

2) single-stranded;

3) ring;

4) double-stranded, but with one shorter chain;

5) double-stranded, but with one continuous and the other fragmented chains.

RNA can be:

1) single-strand;

2) linear double-strand;

3) linear fragmented;

4) ring;

Viral proteins are divided into:

1) genomic - nucleoproteins. Provide replication of viral nucleic acids and virus reproduction processes. These are enzymes, due to which the number of copies of the parent molecule increases, or proteins, with the help of which molecules are synthesized on the nucleic acid matrix that ensure the implementation of genetic information;

2) proteins of the capsid shell - simple proteins with the ability to self-assemble. They add up to geometrically regular structures, in which several types of symmetry are distinguished: spiral, cubic (form regular polygons, the number of faces is strictly constant) or mixed;

3) proteins of the supercapsid shell are complex proteins, diverse in function. Due to them, the interaction of viruses with a sensitive cell occurs. They perform protective and receptor functions.

Among the proteins of the supercapsid shell, there are:

a) anchor proteins (at one end they are located on the surface, while at the other they go into the depth; they provide contact of the virion with the cell);

b) enzymes (can destroy membranes);

c) hemagglutinins (cause hemagglutination);

d) elements of the host cell.

Viruses are classified into those containing DNA (herpes simplex virus) and those containing RNA (human immunodeficiency virus).

According to the structure of capsomeres. Isometric (cubic), spiral, mixed.

By the presence or absence of an additional lipoprotein membrane

Behind the host cells

The most commonly used classification of viruses currently proposed by Nobel Prize winner David Baltimore. It is built on the type of nucleic acid that is used by the virus to carry hereditary material, and on how it is expressed and replicated. It should be noted that such a classification does not reflect the phylogenetic relationships between virus species, since viruses, according to the now generally accepted view, have mechanisms of origin that are different from all other organisms.

Unlike cellular organisms, whose genetic information is stored in the form of double-stranded DNA, the virus genome can be stored in the form of both double- and single-stranded nucleic acids. In this case, this acid can be both DNA and RNA, the matrix form of which (mRNA) is used in cells as an intermediate product in the translation of genetic information in the process of protein synthesis. The RNA genomes of viruses can be encoded in two opposite directions: either the genes are located in the direction from the 5" end of the molecule to the 3" end (positive direction, or + polarity), similar to the direction of genes in mRNA in cells, or genes the viral genome are arranged in the opposite direction (negative direction, or -polarity).

The taxonomy of viruses is basically similar to the taxonomy of cellular organisms. The taxonomic categories used in the classification of viruses are as follows (suffixes for the formation of Latin names are given in brackets):

Row ( -virales)

A family ( -viridae)

Subfamily ( -virinae)

Genus ( -virus)

But in the nomenclature of viruses there are some features that distinguish it from the nomenclature of cellular organisms. Firstly, the names of not only species and genera, but also series and families are written in italics, and secondly, unlike the classical Linnaean nomenclature, the names of viruses are not binomial (i.e. formed from the name of the genus and the epithet of the species - for more details see .. in the article "Scientific classification"). Usually the names of viruses are formed in the form [Disease]-virus.

In general, about 80 families have been described, which include approximately 4000 individual types of viruses.

The distribution of families into rows has begun recently and is proceeding slowly; at present (2005), only three series of diagnostic characters have been identified and described, and most of the described families are unclassified.