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Branches of Virology General virology studies the basic principles of the structure and reproduction of viruses, their interaction with the host cell, the origin and distribution of viruses in nature. One of the most important branches of general virology is molecular virology, which studies the structure and functions of viral nucleic acids, mechanisms of viral gene expression, the nature of organisms’ resistance to viral diseases, and the molecular evolution of viruses. Private virology - studies the characteristics of certain groups of human, animal and plant viruses and develops measures to combat the diseases caused by these viruses. Molecular virology is one of the most important branches of general virology, studying the structure and functions of viral nucleic acids, mechanisms of viral gene expression, the nature of organisms’ resistance to viral diseases, and the molecular evolution of viruses.
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Discovery of viruses The existence of a virus (as a new type of pathogen) was first proven in 1892 by the Russian scientist D.I. Ivanovsky. After many years of research into diseases of tobacco plants, in a work dated 1892, D. I. Ivanovsky comes to the conclusion that tobacco mosaic disease is caused by “bacteria passing through the Chamberlant filter, which, however, are not able to grow on artificial substrates.” Based on these data, the criteria were determined by which pathogens were classified into this new group: filterability through “bacterial” filters, inability to grow on artificial media, and reproduction of the disease picture with a filtrate free of bacteria and fungi. The causative agent of mosaic disease is called by D.I. Ivanovsky in different ways, the term virus had not yet been introduced, allegorically they were called either “filterable bacteria” or simply “microorganisms”)
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Five years later, while studying diseases of cattle, namely foot and mouth disease, a similar filterable microorganism was isolated. And in 1898, when reproducing the experiments of D. Ivanovsky by the Dutch botanist M. Beijerinck, he called such microorganisms “filterable viruses.” In abbreviated form, this name began to denote this group of microorganisms. In 1901, the first human viral disease was discovered - yellow fever. This discovery was made by the American military surgeon W. Reed and his colleagues. In 1911, Francis Rous proved the viral nature of cancer - Rous sarcoma (only in 1966, 55 years later, he was awarded the Nobel Prize in Physiology or Medicine for this discovery
Virology – the science of viruses Anna Fedorenko
Virology is a branch of microbiology that studies viruses (from the Latin word virus - poison).
The existence of a virus (as a new type of pathogen) was first proven in 1892 by the Russian scientist D.I. Ivanovsky. After many years of research into diseases of tobacco plants, in a work dated 1892, D. I. Ivanovsky comes to the conclusion that tobacco mosaic disease is caused by “bacteria passing through the Chamberlant filter, which, however, are not able to grow on artificial substrates.” Based on these data, the criteria by which pathogens were classified into this new group were determined
Five years later, while studying diseases of cattle, namely foot and mouth disease, a similar filterable microorganism was isolated. And in 1898, when reproducing the experiments of D. Ivanovsky by the Dutch botanist M. Beijerinck, he called such microorganisms “filterable viruses.” In abbreviated form, this name began to denote this group of microorganisms.
In 1901, the first human viral disease was discovered - yellow fever. This discovery was made by the American military surgeon W. Reed and his colleagues
In 1911, Francis Rous proved the viral nature of cancer - Rous sarcoma (only in 196, 55 years later, he was awarded the Nobel Prize in Physiology or Medicine for this discovery).
Branches of Virology General Virology General Virology studies the basic principles of the structure and reproduction of viruses, their interaction with the host cell, the origin and distribution of viruses in nature. One of the most important branches of general virology is molecular virology, which studies the structure and functions of viral nucleic acids, mechanisms of viral gene expression, the nature of organisms’ resistance to viral diseases, and the molecular evolution of viruses.
Private virology Private virology studies the characteristics of certain groups of human, animal and plant viruses and develops measures to combat the diseases caused by these viruses.
Molecular virology In 1962, virologists from many countries gathered at a symposium in the USA to summarize the first results of the development of molecular virology. At this symposium, terms that were not entirely familiar to virologists were used: virion architecture, nucleocapsids, capsomeres. A new period in the development of virology began - the period of molecular virology.
Since the late 50s, when a synthetic field of knowledge began to take shape, lying on the border of the inanimate and the living and engaged in the study of the living, the methods of molecular biology poured into virology in an abundant stream. These methods, based on the biophysics and biochemistry of living things, made it possible to quickly study the structure, chemical composition and reproduction of viruses.
If in the 60s the main attention of virologists was fixed on the characteristics of viral nucleic acids and proteins, then by the beginning of the 80s the complete structure of many viral genes and genomes was deciphered and not only the amino acid sequence was established, but also the tertiary spatial structure of such complex proteins , as a glycoprotein of influenza virus hemagglutinin. Currently, it is possible not only to associate changes in the antigenic determinants of the influenza virus with the replacement of amino acids in them, but also to calculate past, present and future changes in these antigens.
Since 1974, a new branch of biotechnology and a new branch of molecular biology - genetic or genetic engineering - began to develop rapidly. She was immediately assigned to the service of virology.
Branches of Virology General virology studies the basic principles of the structure and reproduction of viruses, their interaction with the host cell, the origin and distribution of viruses in nature. One of the most important branches of general virology is molecular virology, which studies the structure and functions of viral nucleic acids, mechanisms of viral gene expression, the nature of organisms’ resistance to viral diseases, and the molecular evolution of viruses. Private virology - studies the characteristics of certain groups of human, animal and plant viruses and develops measures to combat the diseases caused by these viruses. Molecular virology is one of the most important branches of general virology, studying the structure and functions of viral nucleic acids, mechanisms of viral gene expression, the nature of organisms’ resistance to viral diseases, and the molecular evolution of viruses.
Discovery of viruses The existence of a virus (as a new type of pathogen) was first proven in 1892 by the Russian scientist D.I. Ivanovsky. After many years of research into diseases of tobacco plants, in a work dated 1892, D. I. Ivanovsky comes to the conclusion that tobacco mosaic disease is caused by “bacteria passing through the Chamberlant filter, which, however, are not able to grow on artificial substrates.” Based on these data, the criteria were determined by which pathogens were classified into this new group: filterability through “bacterial” filters, inability to grow on artificial media, and reproduction of the disease picture with a filtrate free of bacteria and fungi. The causative agent of mosaic disease is called by D.I. Ivanovsky in different ways, the term virus had not yet been introduced, allegorically they were called either “filterable bacteria” or simply “microorganisms”)
Five years later, while studying diseases of cattle, namely foot and mouth disease, a similar filterable microorganism was isolated. And in 1898, when reproducing the experiments of D. Ivanovsky by the Dutch botanist M. Beijerinck, he called such microorganisms “filterable viruses.” In abbreviated form, this name began to denote this group of microorganisms. Five years later, while studying diseases of cattle, namely foot and mouth disease, a similar filterable microorganism was isolated. And in 1898, when reproducing the experiments of D. Ivanovsky by the Dutch botanist M. Beijerinck, he called such microorganisms “filterable viruses.” In abbreviated form, this name began to denote this group of microorganisms. In 1901, the first human viral disease was discovered - yellow fever. This discovery was made by the American military surgeon W. Reed and his colleagues. In 1911, Francis Rous proved the viral nature of cancer - Rous sarcoma (only in 1966, 55 years later, he was awarded the Nobel Prize in Physiology or Medicine for this discovery
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Kafarskaya Lyudmila Ivanovna
Slide 2: Viruses
Slide 3: Viruses
Viruses (from the Latin virus - poison) are the smallest non-cellular forms of life, standing on the border between living and non-living, having their own genome, capable of reproduction in the cells of living organisms or cell cultures, possessing adaptive properties and variability. The sizes of viruses are measured in nm. 3
Slide 4: Viruses
Groups of viruses: Affecting humans and vertebrates, Birds, fish, arthropods, Plants, microorganisms 4
Slide 5: The discovery of viruses began the development of the science of virology
DI. Ivanovsky (1892) - work on the study of tobacco mosaic disease (plant viruses). The discovery of viruses began the development of the science of virology. He showed that the pathogen is a microorganism capable of passing through bacterial filters and infecting healthy plants, but is not capable of cultivation. 5
Slide 6: Virus discovery
F. Leffler and P. Frosch (1898) - discovery of the virus that causes foot-and-mouth disease in animals; W. Reed and J. Carroll (1901) - isolation of the yellow fever virus in humans; F. d'Herrel and F. Twort (1915 - 1917) discovered viruses in bacteria (bacteriophages). 6
Slide 7: Properties of viruses (virus – poison) Separated into a separate kingdom
Slide 8: Properties of viruses
The presence of a capsid distinguishes viruses from virus-like infectious nucleic acids - viroids. Viroids are plant pathogens that consist of a short fragment (several hundred nucleotides) of circular, single-stranded RNA, not coated with a protein shell. 8
Slide 9: Morphology and structure of viruses
9 Morphology and structure of viruses.
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Slide 10: There are 3 forms of existence of viruses
preservation of the virus in the external environment and transfer it to another cell 10
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Slide 11: Structure of viruses - distinguish between simple and complex
NUCLEOCAPSID 11
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Slide 12: Structure of complex (enveloped) virions
Complex virions have an outer shell (supercapsid), consisting of a two-layer lipid membrane (borrowed from the host cell membrane, the virus acquires when leaving the cell), into which the surface glycoproteins of the virus (influenza viruses, retroviruses) are embedded - the supercapsid. 12
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Slide 13: Structure of complex (enveloped) virions
Viral glycoproteins are responsible for adhesion to cellular receptors and penetration into the cell, and have antigenic properties. From the inside, a layer of matrix protein (M-layer) may be adjacent to the supercapsid 13
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Slide 14: Types of symmetry
The capsid shell consists of many identical protein subunits - capsomeres. There are two ways to package capsomers into a capsid—helical (helical viruses) and cubic (spherical viruses). Simple viruses with a spiral type of symmetry (plant viruses) do not cause diseases in humans 14
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Slide 15: Types of symmetry
With the helical type of symmetry, protein subunits are arranged in a spiral, and between them, in a spiral, the genomic nucleic acid (filamentous viruses) is laid out. The nucleic acid is securely closed, a lot of protein is consumed, but the structure is strong. 15
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Slide 16: Types of symmetry
With a cubic type of symmetry, virions can be in the form of polyhedra, most often twenty-hedra - icosahedrons. The capsid consists of identical protein subunits, while a small amount of genetic information is realized (the genome of viruses is small). 16
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Slide 17: Structure of simple (“naked”) virions
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Slide 18: Structure of viruses
Each capsomere consists of 5 (pentomere) or 6 (sextomer) structural protein units. Cubic symmetry is a combination of equilateral triangles that forms a surface with a cavity inside. Capsids of various viruses from a certain number of capsomeres for a given species (poliomyelitis 32) 18
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Slide 19: Simple virus: adenovirus
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Slide 20: Chemical composition of the virion
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Slide 21: Enveloped influenza virus
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Slide 22: Nucleic acids of viruses
DNA can be: 1) single-stranded (rarely) 2) double-stranded (more often) circular double-stranded, but with one shorter chain double-stranded, but with one continuous and the other fragmented chains. 22
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Slide 23: Nucleic acids of viruses
RNA can be: 1) linear double-stranded (rarely, usually with a fragmented genome) 2) single-stranded (more often) 3) linear fragmented; 4) ring; 5) containing two identical single-stranded RNAs. 23
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Slide 24: Nucleic acids
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Slide 25: Nucleic acids
Viral RNAs are divided into two groups depending on their functions. 1st group - RNA, capable of directly translating genetic information to the ribosomes of a sensitive cell, that is, performing the functions of mRNA.-+RNA (positive genome). They have characteristic endings (“caps”) for specific recognition of ribosomes. 25
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Slide 26: Nucleic acids of viruses
Group 2 – “-” RNA is not capable of translating genetic information directly to ribosomes and functioning as mRNA. “-” RNA serves as a template for the formation of mRNA, i.e. During replication, a template (+RNA) is initially synthesized for the synthesis of -RNA. 26
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Slide 27: Viral RNA
Replication of “-” RNA differs from transcription in the length of the resulting molecules: during replication, the length of the RNA corresponds to the mother strand, and during transcription, shortened mRNA molecules are formed. Transcription is carried out by the virus’s own transcriptases, and both short and long RNAs can be formed, followed by translation of mature proteins or precursor proteins. 27
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Slide 28
Single-stranded RNA viruses, like influenza viruses, have segmented genomes. Replication of these RNA fragments occurs in the nucleus and ends with the creation of several unique mRNAs that encode the structure of a specific protein. In this case, the synthesis of each viral protein is regulated independently. 28
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Slide 29: Single-stranded genomes can have 2 RNA polarities with a positive genome + RNA and a negative genome - RNA
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Slide 30: Virus genome
The genome of viruses contains from 3 to 100 or more genes, which are divided into structural, encoding the synthesis of proteins that make up the virion, and regulatory, which change the metabolism of the host cell and regulate the rate of virus reproduction. thirty
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Slide 31: Virus genome
Viral enzymes are also encoded in the genome. These include: RNA-dependent RNA polymerase (transcriptase), which is found in all negative-sense RNA viruses. Poxviruses contain a DNA-dependent RNA polymerase. 31
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Slide 32: Virus genome
Retroviruses have a unique enzyme, an RNA-dependent DNA polymerase called reverse transcriptase. The genome of some viruses contains genes encoding RNases, endonucleases, and protein kinases 32
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Slide 33: The simplest classification of viruses
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Slide 34: DNA viruses
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Slide 35: DNA viruses
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Slide 36: RNA viruses
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Slide 37: RNA viruses
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Slide 38: Viral proteins - acidic dicarboxylic acids predominate
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Slide 39: Structural proteins
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Slide 40: Non-structural proteins
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Slide 41: Lipids
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Slide 42: Carbohydrates (polysaccharides) of cellular origin
Glycosyl residues of surface proteins - glycoproteins; The process of glycosylation occurs in the Golgi apparatus during the transport of proteins to the outer shell of the supercapsid; Functions: protection against the effects of proteases and binding to antibodies, influence on the correct packaging of proteins. 42
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Slide 43: Structure of HIV
(1) RNA genome of the virus, (2) nucleocapsid, (3) capsid, (4) protein matrix, (5) lipid membrane, (6) gp120 - glycoprotein, (7) gp41 - transmembrane glycoprotein. (8-11) - proteins that are part of the virion and are necessary in the early stages of infection: (8) - integrase, (9) - reverse transcriptase, (10) - Vif, Vpr, Nef and p7, (11) - protease. 43
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Slide 44: Structure of HIV
Surface protein gp41 RNA Surface protein gp 120 Matrix protein p 17 Lipid membrane Capsid protein p 24 Reverse transcriptase AIDS virus 44
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Slide 45: Classification
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Slide 46: Classification
The modern classification is universal. It is based on the fundamental properties of viruses, the leading ones being those characterizing the nucleic acid, the morphology of the viruses, the strategy of the viral genome and antigenic properties. 46
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Slide 47: Classification Criteria
Type of nucleic acid (RNA or DNA) and its primary structure - (single or double stranded, linear, circular, continuous or fragmented). Characteristics of virions: the presence of a protein shell (capsid) and/or an additional lipoprotein shell (supercapsid), size and morphology, type of symmetry. Strategy of the viral genome in the host cell. Antigenic and physicochemical properties. Phenomena of genetic interactions. Ecological interactions (range of susceptible hosts, distribution area). Mechanisms of pathogenicity. Methods of transmission and resistance to environmental factors. 47
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Slide 48: Classification Criteria
All viruses are given Latin names. Domain: Viruses The names of families end in viridae, genera – virus. Scientific names of viruses are written with a capital letter and consist of two Latin words meaning genus (in first place and written with a capital letter) and species (in second place and written with a lowercase letter 48
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Slide 49: Taxonomy of viruses
Based on criteria 1 and 2, viruses are divided into subtypes, orders and families, and based on other characteristics - into genera and species. The classification is determined by the International Committee on Taxonomy of Viruses. The modern database contains 1550 viruses: 3 orders, 56 families (22 pathogenic for humans), 203 genera. 49
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Slide 50: Taxonomy of viruses
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Slide 51: Classification of viruses
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Slide 52: Classification of viruses
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Slide 53: Virus life cycle
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Slide 54: Virus life cycle
A distinctive property of viruses is that they are metabolically inert and cannot independently transform genetic information into new infectious particles, but are able to reproduce in sensitive cells. Reproduction (replication) of viruses is a process during which a virus, using its own genetic material and the synthetic apparatus of the host cell, reproduces offspring similar to itself. 54
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Slide 55: Virus life cycle
Viral replication involves three processes: viral nucleic acid replication, viral protein synthesis, and virion assembly. The reproduction cycle of viruses varies from 6-8 hours (picornaviruses) to 40 hours or more (some herpesviruses). Virus replication at the single cell level consists of several successive stages: 55
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Slide 56: Life cycle stages
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Slide 57: Virus life cycle
The passage of all these stages constitutes one reproduction cycle. Reproduction of the virus is accompanied by suppression of the biological functions of the cell and disturbances in cellular metabolism, and complete destruction of the cell with the release of viral progeny is possible (cytopathogenic effect) 57
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Slide 58: Virus life cycle
The first stages of the development of a virus in a cell, in general terms, consist in the construction of early proteins, enzyme proteins necessary for the virus to replicate (double) their nucleic acid. Late proteins are involved in the formation of protein shells of daughter viral particles 58
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Slide 59
Vesicle with envelope Endosome Translation Budding Endoplasmic reticulum Golgi apparatus Synthesis of envelope proteins Nucleus 59
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Slide 60: 1. Adsorption
Glycoprotein (complex) or protein (simple) viruses interacts with a receptor on the cell surface (glycoproteins, glycolipids, etc.) Virus tropism is the ability of a virus to infect a certain range of specialized cells. Adsorption of herpes virus on the cytoplasmic membrane 60
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Slide 61: Adsorption
The initial stages of adsorption are nonspecific and are caused by the electrostatic interaction of virions and the cell membrane. Ca2+ ions are required (neutralize excess anionic charges of the virus and cell surface, reduce electrostatic repulsion). The process is reversible. 61
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Slide 62: Adsorption
Approximately 104-106 receptor molecules (binding sites) are expressed on the cell membrane. There are high-affinity receptors (primary) and co-receptors (secondary) or low-affinity. Initially, single sections of the virion bind to the primary receptor; it is not strong. Irreversible adsorption is observed with multiple connections of the virion with cell receptors (stable multivalent binding). 62
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Slide 63: 1. Adsorption
The AIDS virus attaches to the CD4 glycoprotein on T-helper cells, and the antireceptor of the virus is the gp 120 glycoprotein. Effective adsorption of HIV requires coreceptors (chemokine receptors on T-helper cells). 63
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Slide 64: Adsorption
Often, the binding of viruses to cells leads to irreversible changes in the structure of the virion. When penetration does not occur, the virus can separate from the cell and re-adsorb onto another (orthomyxoviruses and paramyxoviruses), which carry neuraminidase on their surface. These viruses can be separated from their receptors by the cleavage of neuraminic acid from the polysaccharide chain of the receptors. 64
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Slide 65: 2. Penetration is an energy dependent process and occurs almost instantly after attachment
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Slide 66: Virus penetration into a cell
Penetration begins after adsorption, requires energy, and does not occur at 0°C. After adsorption, the whole virion or genome and polymerases penetrate into the cell through the cytoplasmic membrane at the “hole” with the clathrin protein, where the receptor is located. Simple viruses (polioviruses) undergo a process of receptor-dependent endocytosis (viropexis) and appear in the cytoplasm in the form of vesicles (endosomes). Endosomes can subsequently fuse with lysosomes 66
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Slide 67: 2.Penetration: endocytosis
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Slide 68: 2. Entry: endocytosis
Cell membrane Endosome Lysosome Release of nucleocapsid Enveloped vesicle Adsorption of virion Fusion of virus and endosome membranes Bordered pit 68
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Slide 69: Penetration: endocytosis
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Slide 70: Complex viruses-penetration
To penetrate the cell, 2 methods are used. First: after binding to specific receptors, they cause their aggregation and form an invagination in the membrane (immersion pit). The proton pump reduces the pH in the endosome to 5.0, the hydrophobic components of the virus polypeptides change, which promotes their fusion with the endosome membrane and penetration into the cytoplasm by receptor-dependent endocytosis. 70
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Slide 71: Fusion of the supercapsid shell of the virus with the cell membrane
One of the surface proteins (fusion protein) interacts with the lipid bilayer of the cell; as a result, the lipid bilayers of the virus and the cell merge into a common membrane. The contents of the virion pass into the cell, and the virion envelope remains on the surface of the cell. Fusion of the supercapsid shell of the virus with the cell membrane 71
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Slide 72: 2. Penetration - membrane fusion
Penetration of the human immunodeficiency virus into lymphatic tissue 2. Penetration - fusion of membranes 72
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Slide 73: “Undressing” (deproteinization) and transport to the replication site
Deproteinization is the process of removing or disintegrating part or all of the protein coat of a virus in order to make the genome accessible to cellular transcription and translation mechanisms. 73
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Slide 74: 3. “Undressing” (deproteinization) and transport to the replication site
Proteolytic enzymes of the cell remove completely or partially the capsid shell 74
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Slide 75: 5. Virion assembly, maturation and release from cells
Simple viruses are formed by self-assembly: nucleic acid interacts with capsid proteins; Complex viruses are formed in several stages: first, the nucleocapsid is formed, interaction with cell membranes (external or internal) 5. Assembly of virions, maturation and exit from cells 75
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Slide 76: Virion assembly, maturation and release from cells
“dressing” with a supercapsid shell from the host cell membrane; In some viruses, a protein M-layer is formed under the shell. 76
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Slide 77: 5. Virion assembly, maturation and release from cells
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Slide 78: 5. Budding
The nucleic acid and capsid protein of the virus are assembled into a nucleocapsid; Glycoprotein precursor proteins pass through the ER and Golgi apparatus; Mature glycoproteins are integrated into the plasma membrane of cells, displacing host glycoproteins; The nucleocapsid interacts with glycoproteins and a complex is formed that undergoes exocytosis. 78
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Slide 79: 5. Budding
Electron micrograph of a C-type retrovirus of the MLV group at different stages of virion formation 1 - Initial stage of virion formation 2 - Budding of the virion 3 - Mature virion 79
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Slide 80: Budding
In some cases (ortho- and paramyxoviruses), during or after protrusion, cutting and structural rearrangement of one of the surface proteins occurs, which gives the newly formed virion the ability to infect cells. 80
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Slide 81: 5. Cytolysis
Assembly is completed in the nucleus or cytoplasm of the host cell; The virus disrupts the vital activity of the cell and leads to its death (necrotic death); Cellular enzymes destroy the cytoplasmic membrane; The virus enters the extracellular environment. 81
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Slide 82: Cytolysis
Disintegration of infected cells is a prerequisite for the release of all viruses that assemble and acquire infectivity intracellularly 82
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Slide 83: Virus reproduction
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Slide 84: Virus reproduction
The key point in viral replication is the use of host protein-synthesizing structures for viral synthesis. The virus must provide the protein-synthesizing apparatus of the eukaryotic cell with mRNA, which the cell must recognize and translate. 84
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Slide 85: Virus reproduction
in the host cell: a) neither in the nucleus nor in the cytoplasm are there enzymes necessary for transcription of mRNA from the viral RNA genome, b) in the cytoplasm there are no enzymes capable of transcribing viral DNA. 85
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Slide 86: Virus reproduction
Cellular transcriptase for the synthesis of viral mRNAs can only be used by viruses that contain DNA and are able to penetrate the nucleus. All other viruses are forced to create their own enzymes to synthesize mRNA. 86
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Slide 87: Virus reproduction
The synthesizing apparatus of eukaryotic cells is adapted only for the translation of monocistronic mRNAs, since it does not recognize internal initiation sites in mRNA. Viruses are forced to synthesize either separate mRNAs for each gene (monocistronic mRNA), or an mRNA that includes several genes and encodes a “polyprotein”, which is then cut into individual proteins. 87
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Slide 88: Stages of reproduction
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Slide 89: Virus reproduction
Translation occurs on cellular ribosomes, on which the synthesis of cellular proteins is suppressed and viral proteins are translated. There are 2 ways of forming viral proteins depending on the length of the mRNA. Short, monocistronic mRNAs encode a separate, mature viral protein. 89
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Slide 90
Long polycistronic RNAs bind to polyribosomes, the giant polyprotein precursor is translated, cut by viral and cellular proteases into individual viral (structural and nonstructural proteins) 90
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Slide 91: Virus reproduction
Viruses belonging to different families use different types of genome strategies to achieve the ultimate goal - the formation of mature offspring. Viruses containing double-stranded DNA synthesize mRNA in the same way as the host cell, using DNA-dependent RNA polymerase. 91
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Slide 92: Reproduction of double-stranded DNA viruses (class I)
Replication by the usual mechanism, usually in the nucleus (exception: poxviruses); Host cell RNA polymerase is involved in transcription; viral proteins regulate its activity; Short early and late mRNAs are formed, on which early and late proteins are synthesized; For translation, viruses use the cellular protein biosynthesis apparatus (ribosomes and translation factors); Complex viruses can have their own DNA polymerase and synthesize their own proteins 92
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Slide 93: Reproduction of double-stranded DNA viruses (class I)
Double-stranded DNA viruses contain NAs of linear (herpes-, adeno- and poxviruses) and ring-shaped (papovaviruses) forms. Replication of double-stranded viral DNA proceeds by the usual semi-conservative mechanism: after the DNA strands unwind, new strands are complementarily added to them. In all viruses except poxviruses, transcription of the viral genome occurs in the nucleus. 93
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Slide 94
DNA i-RNA Transcription Early proteins Translation of i-RNA Late proteins Copies of DNA Reproduction of double-stranded DNA viruses (class I) Progeny of the virus 94
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Slide 95: Reproduction of double-stranded DNA viruses (class I)
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Slide 96: Reproduction of single-stranded DNA (Class II)
Representatives of single-stranded DNA viruses are parvoviruses. The viral genome enters the cell nucleus, and cellular DNA polymerases are used to create a double-stranded viral genome, a replicative form. In this case, on the original viral DNA (+ strand), a minus strand of DNA is complementarily synthesized, which serves as a matrix in the synthesis of plus strand DNA for new generations of viruses. At the same time, mRNA is synthesized and viral proteins are translated, which return to the nucleus, where virions are assembled. 96
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Slide 97: Reproduction of single-stranded DNA (Class II)
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Slide 98
s/s DNA Transcription Cellular proteins mRNA Proteins d/s DNA Reproduction of single-stranded DNA viruses (class II) Progeny of the virus 98
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Slide 99: Reproduction of single-stranded DNA viruses (class II)
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Slide 100: Reproduction of double-stranded RNA viruses (Class III)
This group includes reo- and rotaviruses; they have a segmented genome, the mRNA of each segment encodes a separate polypeptide chain. The process of viral nucleic acid replication, transcription and translation occurs in the cytoplasm of the cell. The information contained in double-stranded RNA must first be copied into single-stranded (+) RNA, which functions as mRNA. 100
Slide 106: Reproduction of single-stranded (+)RNA viruses (class IV)
Virus-encoded RNA polymerase (RNA transcriptase) synthesizes the complementary (-) strand of RNA using genomic RNA as a template. Newly synthesized (-) RNA molecules are stored as a template for further production of the required amount of genomic (+) strand RNA. 106
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Slide 107: Reproduction of single-stranded (+)RNA viruses (class IV)
Newly formed RNA molecules can be stored in the cytoplasm as mRNA or used as precursor molecules for virion (genomic) RNA. The process is completed by self-assembly of virions and packaging of genomic +RNA into capsids. 107
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Slide 108: Reproduction of single-stranded (+)RNA viruses (class IV)
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Slide 116: Reproduction of retroviruses
Double-stranded DNA copies of the genome take a circular form, are transported into the nucleus and integrated (with the help of integrase) into the DNA of the chromosome, a “provirus” is formed, transcribed by cellular RNA polymerases, and mRNA molecules identical to the viral genome are created. 116
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Slide 117: Reproduction of retroviruses
The molecules of these RNAs are transported into the cytoplasm in an unspliced form or in the form of several spliced mRNAs. Genomic RNA is a messenger for the translation of a series of polyprotein molecules. The protease then cleaves the polyprotein molecule into polypeptides, the precursors of individual structural and non-structural proteins. Retroviruses are characterized by a combination of integrative and productive infection 117
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Slide 122: Features of viral infections
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Slide 123: Features of viral infections
Viral infections occur in the form of a productive (acute) infection or persistence. A productive, or acute, viral infection is accompanied by the reproduction of virions in the host cells and the rapid release of the pathogen from the body. Persistence is characterized by the long-term presence of the virus in the human body. Persistence of a viral infection manifests itself in a latent, chronic and slow form. 123
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Slide 124: Features of viral infections
Latent asymptomatic infection is characterized by long-term, possibly lifelong carriage of the virus, which does not leave the body and is not released into the environment. This is due to its defectiveness, as a result of which it cannot reproduce with the formation of a full-fledged virus or the formation of a state of virogenesis, characterized by the incorporation of viral nucleic acid into the genome of the cell and being in a repressive state 124
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Slide 125: Features of viral infections
As a result of synchronous replication with cellular DNA, the virus is transmitted to new cells. Sometimes, when the repressor is inactivated, the virus reproduces, the progeny leaves the cell, and as a result, the development of an acute (productive) infection is observed 125
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Slide 126
A latent infection in the form of virogeny occurs with herpes. Spontaneous activation of viral information contained in the cell genome leads to relapses of the disease throughout a person’s life. 126
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Slide 127
Form 2 persistence occurs as a chronic infection, accompanied by periods of improvement and exacerbation over many months and even years. In this case, the virus is periodically released from the patient’s body. Chronic infection can be caused by adenoviruses 127
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Last presentation slide: Virology
The third form of persistence is slow infections. They are characterized by a very long incubation period, the duration of which is estimated at many months and even years. There is a gradual increase in symptoms of the disease, ending in severe disorders or death of the patient 128
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Characteristics of virology as a science: discovery of viruses; principles of modern classification of viruses, their groups, chemical composition, physical structure; properties of viral nucleic acids; viral proteins, their features; biosynthesis of DNA-containing viruses.
cheat sheet, added 05/23/2014
History of the study of viruses, the creation of their synthetic analogues. Structure, structure and classification of bacteriophages. Stages of infection and penetration into the cell. Activation of the body's immune system. Bypassing protection and initiating translation of the RNA body of the virus.
abstract, added 04/01/2014
History of the development of microbiology, virology and immunology, subject, tasks, methods. Systematics, morphology and ecology of microorganisms. Classification, structure and features of the biology of viruses. Biotechnology and genetic engineering. Types and mechanisms of immunity.
course of lectures, added 03/13/2015
The place of viruses in the biosphere. Evolutionary origin. Structure and properties. Classification. Bacteriophages. Life cycle of viruses. Cancer problems. Oncogenic effect of viruses. The mechanism of the transforming effect of oncogenic viruses on the cell. Interferon.
abstract, added 07/17/2008
Structure and basic properties of viruses. Life cycle of bacteriophages. Oncogenic effect of viruses. Features of the transduction phenomenon. The mechanism of the transforming effect of oncogenic viruses on the cell. Clinical use of interferon and its products.
abstract, added 09/30/2009
The concept of a virus as a non-cellular life form, their vital activity when they enter a bacterial or eukaryotic cell. Diversity of virus structure. History of the study of viruses, main symptoms, routes of their transmission and methods of therapeutic therapy.
presentation, added 04/25/2016
The formation of virology as a science. Development of a cell culture method, research of encephalitis viruses. Study of the control of gene expression in prokaryotic organisms. Conducting molecular genetic research. Chemical composition of complex virions.
abstract, added 11/12/2013
History of the discovery of viruses. Discovery of the first human viral disease, yellow fever, in 1901. Helical and icosahedral capsids. The structure of T-phage Escherichia coli with a mixed type of symmetry. Classes of DNA-containing tumor viruses.
abstract, added 06/07/2016
The nature and origin of viruses, their components, structure, classification and features of interaction with the cell. The significance of the results of the experiments of Hershey and Chase for the development of genetics. Methods of transmission of viral diseases. Biological role of viruses.
