Composition, size and shape. Viruses

Mankind became acquainted with viruses at the end of the 9th century, after the works of Dmitry Ivanovsky and Martin Beyerink. Studying non-bacterial lesions of tobacco plants, scientists for the first time analyzed and described 5 thousand types of viruses. Today it is assumed that there are millions of them and they live everywhere.

Alive or not?

Viruses consist of DNA and RNA molecules that transmit gene information in various combinations, an envelope that protects the molecule, and additional lipid protection.

The presence of genes and the ability to reproduce makes it possible to classify viruses as living, and the lack of protein synthesis and the impossibility of independent development classifies them as non-living biological organisms.

Viruses are also capable of alliance with bacteria and mutating. They can transmit information through RNA exchange and evade the immune response, ignoring drugs and vaccines. The question of whether the virus is alive remains open to this day.

The most dangerous enemy

Today, a virus that does not respond to antibiotics is human's worst enemy. Opening antiviral drugs eased the situation a little, but AIDS and hepatitis are still not defeated.

Vaccines provide protection against only a few seasonal strains of viruses, but their ability to quickly mutate makes vaccinations ineffective the next year. The most serious threat to the world's population may be the inability to cope with the next viral epidemic in time.

Influenza is only a small part of the "viral iceberg". The Ebola virus infection in Africa has led to the introduction of quarantine measures around the world. Unfortunately, the disease is extremely difficult to treat, and the percentage of deaths is still high.

A feature of viruses is their incredibly fast ability to multiply. The bacteriophage virus is capable of exceeding the bacterium in reproduction rate by 100 thousand times. Therefore, virologists from all over the world are trying to save humanity from a deadly threat.

The main measures for the prevention of viral infections are: vaccinations, adherence to personal hygiene rules and timely access to a doctor in case of infection. One of the symptoms was heatthat cannot be brought down on your own.

You shouldn't panic if you have a viral illness, but being careful can literally save your life. Doctors say that infections will mutate as long as human civilization will exist, and scientists still have many important discoveries in the origin and behavior of viruses, as well as in the fight against them.

Plan:

Introduction

• 1. History
• 2 Structure
• 3 The role of viruses in the biosphere
• 4 Position of viruses in the living system
• 5 Origin of viruses
• 6 Structure
• 7 Infection mechanism
• 8 Classification
  • 8.1 ICTV classification
  • 8.2 Baltimore classification
• 9 Interesting Facts
Notes
Literature

Introduction

Virus (from lat. virus - poison) is a subcellular infectious agent that can only reproduce inside living cells of the body. By nature, viruses are autonomous genetic elements that have an extracellular stage in the developmental cycle. Viruses are microscopic particles consisting of nucleic acid molecules - (DNA or RNA, some, for example, mimiviruses, have both types of molecules), enclosed in a protein shell, capable of infecting living organisms. The protein envelope in which the genome is packed is called the capsid. The presence of a capsid distinguishes viruses from virus-like infectious nucleic acids - viroids. Viruses, with rare exceptions, contain only one type of genomic nucleic acid; they classify DNA-containing viruses and RNA-containing viruses, on which the Baltimore classification of viruses is based. Previously, prions were also mistakenly attributed to viruses, but later it turned out that these pathogens are special infectious proteins and do not contain nucleic acids.

Currently, viruses are known that multiply in the cells of plants, animals, fungi and bacteria (the latter are usually called bacteriophages or phages). Despite some general patterns of structure and development strategy (associated with a functional community), viruses do not have a common origin. This is confirmed by the fact that the genomes of viruses infecting groups of organisms that are distant among themselves are structurally related, but, moreover, have a common structure of genes and regulatory elements, encode structurally similar proteins, and have common mechanisms for regulating gene expression. Viruses that infect other viruses (satellite viruses) have also been detected.

1. History

For the first time, the existence of a virus (as a new type of pathogen) was proved in 1892 by the Russian scientist D.I.Ivanovsky. After many years of research on diseases of tobacco plants, in a work dated 1892, DI Ivanovsky comes to the conclusion that tobacco mosaic is caused by "bacteria passing through the Chamberlain filter, which, however, are not able to grow on artificial substrates."

Five years later, in the study of diseases in cattle, namely, foot and mouth disease, a similar filterable microorganism was isolated. And in 1898, while reproducing the experiments of D. Ivanovsky by the Dutch botanist M. Beijerinck, he called such microorganisms "filterable viruses." In an 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. Read and his colleagues.

In 1911, Francis Routh proved viral nature cancer - Rous sarcoma (only in 1966, 55 years later, he was awarded the Nobel Prize in Physiology or Medicine for this discovery).

In subsequent years, the study of viruses played an important role in the development of epidemiology, immunology, molecular genetics, and other branches of biology. Thus, the Hershey-Chase experiment became decisive proof of the role of DNA in the transmission of hereditary properties. Over the years, at least six more Nobel Prizes in Physiology or Medicine and three Nobel Prizes in Chemistry were awarded for research directly related to the study of viruses.

In 2002, the first synthetic virus (polio virus) was created at New York University.

2. Structure

Simply organized viruses are composed of a nucleic acid and several proteins that form an envelope around it - capsid... An example of such viruses is the tobacco mosaic virus. Its capsid contains one type of protein with a small molecular weight. Complexly organized viruses have an additional envelope - protein or lipoprotein; sometimes in the outer shells of complex viruses, in addition to proteins, carbohydrates are contained. The causative agents of influenza and herpes are examples of complexly organized viruses. Their outer membrane is a fragment of the nuclear or cytoplasmic membrane of the host cell, from which the virus enters the extracellular environment.

3. The role of viruses in the biosphere

Viruses are one of the most common forms of the existence of organic matter on the planet in terms of numbers: the waters of the oceans contain a colossal number of bacteriophages (about 250 million particles per milliliter of water), their total number in the ocean is about 4 × 10 30, and the number of viruses (bacteriophages) in ocean bottom sediments practically does not depend on depth and is very high everywhere. The ocean is home to hundreds of thousands of species (strains) of viruses, the overwhelming majority of which have not been described, much less studied. Viruses play an important role in the regulation of the population size of some species of living organisms (for example, the wildness virus reduces the number of Arctic foxes several times every few years).

4. Position of viruses in the living system

5. Origin of viruses

Viruses are a collective group that has no common ancestor. Currently, there are several hypotheses explaining the origin of viruses.

The origin of some RNA viruses is associated with viroids. Viroids are highly structured circular RNA fragments replicated by cellular RNA polymerase. It is believed that viroids are "escaped introns" - insignificant regions of mRNA cut out during splicing, which accidentally acquired the ability to replicate. Viroids do not encode proteins. It is believed that the acquisition of coding regions (open reading frame) by viroids led to the appearance of the first RNA viruses. Indeed, examples of viruses are known that contain pronounced viroid-like regions (hepatitis Delta virus).

Examples of structures of icosahedral virions.
A. Virus that does not have a lipid envelope (eg, picornavirus).
B. An enveloped virus (eg herpesvirus).
The numbers indicate: (1) capsid, (2) genomic nucleic acid, (3) capsomere, (4) nucleocapsid, (5) virion, (6) lipid envelope, (7) membrane proteins of the envelope.

Viral particles (virions) are a protein capsule - a capsid containing the virus genome, represented by one or more DNA or RNA molecules. The capsid is built from capsomers - protein complexes, consisting, in turn, of protomers... Nucleic acid in a complex with proteins is denoted by the term nucleocapsid... Some viruses also have an outer lipid membrane. Dimensions various viruses range from 20 (parvoviruses) to 500 (mimiviruses) and more nanometers. Virions often have a regular geometric shape (icosahedron, cylinder). Such a capsid structure provides for the identity of the bonds between its constituent proteins, and, therefore, can be built from standard proteins of one or several types, which allows the virus to save space in the genome.

7. The mechanism of infection

Conventionally, the process of viral infection on the scale of one cell can be divided into several overlapping stages:

A rod-shaped particle of the tobacco mosaic virus.
The numbers indicate: (1) the RNA genome of the virus, (2) the capsomere, consisting of only one protomer, (3) the mature region of the capsid.

• Attachment to the cell membrane - the so-called adsorption. Usually, in order for a virion to be adsorbed on the surface of a cell, it must have a protein (often a glycoprotein) in its plasma membrane - a receptor specific for this virus. The presence of a receptor often determines the range of hosts of a given virus, as well as its tissue specificity.

The structure of the virion of a nonicosahedral enveloped virus as exemplified by HIV.
The numbers indicate: (1) the RNA genome of the virus, (2) the nucleocapsid, (3) the capsid, (4) the protein matrix underlying (5) the lipid membrane, (6) gp120 is the glycoprotein by which the virus binds to the cell membrane , (7) gp41 is a transmembrane glycoprotein.
The numbers 8-11 indicate the proteins that make up the virion and are necessary for the virus to early stages infections: (8) integrase, (9) reverse transcriptase, (10) Vif, Vpr, Nef and p7, (11) protease.

In the taxonomy of wildlife, viruses are separated into a separate taxon Vira, forming in the Systema Naturae 2000 classification together with the domains Bacteria, Archaea and Eukaryota root taxon Biota... During the XX century, in systematics, proposals were made to create a dedicated taxon for non-cellular life forms ( Aphanobionta Novak, 1930; the super-kingdom of Acytota Jeffrey, 1971; Acellularia), however such proposals have not been codified.

The taxonomy and taxonomy of viruses is codified and maintained by the International Committee on Taxonomy of Viruses (ICTV), which also maintains The Universal Virus Database ICTVdB.

8.1. ICTV classification

In 1966, the International Committee on the Taxonomy of Viruses adopted a classification system for viruses based on the difference in type (RNA and DNA), the number of nucleic acid molecules (single- and double-stranded) and on the presence or absence of a nuclear envelope. The classification system is a series of hierarchical taxa:

Detachment ( -virales) Family ( -viridae) Subfamily ( -virinae) Genus ( -virus) View ( -virus)

8.2. Baltimore classification

Nobel laureate biologist David Baltimore proposed his own classification scheme for viruses based on differences in the mechanism of mRNA production. This system includes seven main groups:

• (I) Viruses containing double-stranded DNA and lacking an RNA stage (for example, herpes viruses, poxviruses, papovaviruses, mimivirus).
• (Ii) Viruses containing double-stranded RNA (eg rotaviruses).
• (III) Viruses containing a single-stranded DNA molecule (eg parvoviruses).
• (Iv) Viruses containing a single-stranded RNA molecule of positive polarity (eg, picornaviruses, flaviviruses).
• (V) Viruses containing a single-stranded RNA molecule of negative or double polarity (eg, orthomyxoviruses, filoviruses).
• (VI) Viruses containing a single-stranded RNA molecule and having in their life cycle the stage of DNA synthesis on an RNA template, retroviruses (for example, HIV).
• (VII) Viruses containing double-stranded DNA and having in their life cycle a stage of DNA synthesis on an RNA matrix, retroid viruses (for example, hepatitis B virus).

Currently, for the classification of viruses, both systems are used simultaneously, as complementary to each other.

Further division is carried out on the basis of such traits as the structure of the genome (the presence of segments, circular or linear molecules), genetic similarity with other viruses, the presence of a lipid membrane, taxonomic affiliation of the host organism, and so on.

9. Interesting facts

• In 2008, V.D. Zorkin noted that popular human rights defenders, speaking in European parliaments, demanded legislative protection of the rights of viruses, and he also noted there that ultra-extremists who were convinced that a person is a hostile virus were alongside supporters of the rights of viruses. which should be destroyed in the name of preserving nature.

Notes

1. Cello J, Paul AV, Wimmer E (2002). Chemical synthesis of poliovirus cDNA: generation of infectious virus in the absence of natural template. Science 297 (5583): 1016-8. DOI: 10.1126 / science.1072266 - dx.doi.org/10.1126/science.1072266. PMID 12114528 - www.ncbi.nlm.nih.gov/pubmed/12114528?dopt\u003dAbstract.
2. Bergh O, Børsheim KY, Bratbak G, Heldal M (August 1989). "High abundance of viruses found in aquatic environments." Nature 340 (6233): 467-8. DOI: 10.1038 / 340467a0 - dx.doi.org/10.1038/340467a0. PMID 2755508 - www.ncbi.nlm.nih.gov/pubmed/2755508?dopt\u003dAbstract.
3. 1 2 Elements - science news: By destroying bacterial cells, viruses actively participate in the circulation of substances in the depths of the ocean - elementy.ru/news/430811
4. PLoS Biology: The Marine Viromes of Four Oceanic Regions - www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0040368
5. Elements - science news: Hundreds of thousands of new types of viruses have been discovered in the ocean - elementy.ru/news/430383
6. ScienceNow - "Ancient Virus Gave Wasps Their Sting" - news.sciencemag.org/sciencenow/2009/02/12-02.html?rss\u003d1
7. Elements - science news: riders suppress the immune defenses of their victims with tamed viruses - elementy.ru/news/431008
8. Baltimore D (1974). "The strategy of RNA viruses". Harvey Lect. 70 Series: 57-74. PMID 4377923 - www.ncbi.nlm.nih.gov/pubmed/4377923?dopt\u003dAbstract.
9. Temin HM, Baltimore D (1972). "RNA-directed DNA synthesis and RNA tumor viruses." Adv. Virus Res. 17 : 129–86. PMID 4348509 - www.ncbi.nlm.nih.gov/pubmed/4348509?dopt\u003dAbstract.
10. van Regenmortel MH, Mahy BW (2004). “Emerging issues in virus taxonomy”. Emerging Infect. Dis. 10 (1): 8-13. PMID 15078590 - www.ncbi.nlm.nih.gov/pubmed/15078590?dopt\u003dAbstract.
11. Mayo MA (1999). “Developments in plant virus taxonomy since the publication of the 6th ICTV Report. International Committee on Taxonomy of Viruses ". Arch. Virol. 144 (8): 1659–66. PMID 10486120 - www.ncbi.nlm.nih.gov/pubmed/10486120?dopt\u003dAbstract.
12. de Villiers EM, Fauquet C, Broker TR, Bernard HU, zur Hausen H (2004). "Classification of papillomaviruses". Virology 324 (1): 17-27. DOI: 10.1016 / j.virol.2004.03.033 - dx.doi.org/10.1016/j.virol.2004.03.033. PMID 15183049 - www.ncbi.nlm.nih.gov/pubmed/15183049?dopt\u003dAbstract.
13. "Constitution and human rights in the XXI century" - www.ozon.ru/context/detail/id/4181595/ Chairman of the Constitutional Court of the Russian Federation, Honored Lawyer of the Russian Federation, Doctor of Law, Professor V.D. Zorkin: “How else to call the proposals to defend not only human rights, but also animal rights in parliaments, electing deputies from various animal species? But the popular radicals proclaiming this have agreed to the point that it is necessary to protect the rights of viruses and approve legislation of the appropriate format. " (pp. 21-22), ISBN 978-5-468-00282-7, Virology.
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the smallest pathogens of infectious diseases. Translated from Latinvirus means "poison, poisonous principle." Until the end of the 19th century. the term "virus" has been used in medicine to refer to any infectious agent that causes disease. This word acquired its modern meaning after 1892, when the Russian botanist DI Ivanovsky established the "filterability" of the causative agent of tobacco mosaic disease (tobacco mosaic). He showed that cell sap from plants infected with this disease, passed through special filters that trap bacteria, retains the ability to cause the same disease in healthy plants. Five years later, another filterable agent, the causative agent of foot and mouth disease in cattle, was discovered by the German bacteriologist F. Löffler. In 1898, the Dutch botanist M. Beijerink repeated these experiments in an expanded version and confirmed Ivanovsky's conclusions. He called the "filterable poisonous principle" causing the tobacco mosaic a "filterable virus." This term has been used for many years and has gradually been reduced to a single word - "virus".

In 1901, the American military surgeon W. Reed and his colleagues found that the causative agent of yellow fever is also a filterable virus. Yellow fever was the first human disease to be identified as viral, but it took another 26 years for its viral origin to be definitively proven.

It is generally accepted that viruses arose as a result of the isolation (autonomy) of individual genetic elements of the cell, which, in addition, received the ability to be transmitted from organism to organism. In a normal cell, several types of genetic structures move, for example, matrix, or informational, RNA (mRNA), transposons, introns, and plasmids. Such mobile elements may have been the predecessors, or progenitors, of viruses.

Some viruses, in addition to the capsid, also have an outer envelope consisting of proteins and lipids. It is formed from the membranes of the infected cell containing embedded viral proteins. The terms "naked virions" and "uncoated virions" are used synonymously. The capsids of the smallest and most simply arranged viruses can consist of only one or several types of protein molecules. Several molecules of the same or different proteins are combined into subunits called capsomeres. Capsomeres, in turn, form regular geometric structures of the viral capsid. In different viruses, the capsid shape is a characteristic feature (feature) of the virion.

Virions with a spiral type of symmetry, like the tobacco mosaic virus, have the shape of an elongated cylinder; inside the protein sheath, which consists of separate subunits - capsomeres, there is a coiled nucleic acid (RNA) helix. Virions with an icosahedral type of symmetry (from the Greek.

eikosi - twenty, hedra - surface), like poliovirus, have a spherical, or rather, a multifaceted shape; their capsids are built of 20 regular triangular facets (surfaces) and look like a geodesic dome.

Individual bacteriophages (bacteria viruses; phages) have a mixed type of symmetry. At the so-called. Of "tailed" phages, the head looks like a spherical capsid; a long tubular process - "tail" departs from it.

There are viruses with an even more complex structure. Poxvirus virions (smallpox viruses) do not have a regular, typical capsid: tubular and membrane structures are located between the core and the outer shell.

REPLICATION OF VIRUSES Genetic information encoded in a particular gene can generally be seen as instructions for the production of a particular protein in a cell. Such an instruction is perceived by the cell only if it is sent in the form of mRNA. Therefore, cells in which the genetic material is represented by DNA must "rewrite" (transcribe) this information into a complementary copy of mRNA (see also NUCLEIC ACIDS) ... DNA-containing viruses in the way of replication differ from RNA-containing viruses.

DNA usually exists in the form of double-stranded structures: two polynucleotide chains are hydrogen-bonded and twisted in such a way that a double helix is \u200b\u200bformed. RNA, in contrast, usually exists in the form of single-stranded structures. However, the genome of individual viruses is either single-stranded DNA or double-stranded RNA. Strands (chains) of viral nucleic acid, double or single, can be linear or closed in a ring.

The first stage of viral replication is associated with the penetration of the viral nucleic acid into the host cell. This process can be facilitated by special enzymes that are part of the capsid or outer shell of the virion, and the shell remains outside the cell or the virion loses it immediately after penetrating into the cell. The virus finds a cell suitable for its reproduction by contacting individual parts of its capsid (or outer shell) with specific receptors on the cell surface in a "key-lock" manner. If specific (“recognizing”) receptors on the cell surface are absent, then the cell is not sensitive to viral infection: the virus does not penetrate into it.

In order to realize its genetic information, the viral DNA that has penetrated into the cell is transcribed by special enzymes into mRNA. The resulting mRNA moves to the cellular "factories" of protein synthesis - ribosomes, where it replaces cellular "messages" with its own "instructions" and is translated (read), as a result of which viral proteins are synthesized. The viral DNA itself is repeatedly duplicated (duplicated) with the participation of another set of enzymes, both viral and belonging to the cell.

The synthesized protein, which is used to build the capsid, and the viral DNA multiplied in many copies combine and form new, "daughter" virions. The formed viral progeny leaves the used cell and infects new ones: the virus reproduction cycle repeats. Some viruses, during budding from the cell surface, capture a part of the cell membrane, into which viral proteins have been inserted "in advance", and thus acquire a membrane. As for the host cell, it eventually turns out to be damaged or even completely destroyed.

In some DNA viruses, the reproduction cycle itself in the cell is not associated with the immediate replication of viral DNA; instead, the viral DNA is inserted (integrated) into the DNA of the host cell. At this stage, the virus as a single structural formation disappears: its genome becomes part of the genetic apparatus of the cell and even replicates as part of the cellular DNA during cell division. However, subsequently, sometimes after many years, the virus may appear again - the mechanism of synthesis of viral proteins is triggered, which, combining with viral DNA, form new virions.

In some RNA viruses, the genome (RNA) can directly act as mRNA. However, this feature is typical only for viruses with a "+" RNA strand (ie, with RNA having a positive polarity). Viruses with "

- "The RNA strand must first" overwrite "the" + "strand; only after that the synthesis of viral proteins begins and the virus replicates.

The so-called retroviruses contain RNA as their genome and have an unusual way of transcribing genetic material: instead of transcribing DNA into RNA, as it happens in a cell and is typical for DNA-containing viruses, their RNA is transcribed into DNA. The double-stranded DNA of the virus is then incorporated into the chromosomal DNA of the cell. On the matrix of such viral DNA, new viral RNA is synthesized, which, like others, determines the synthesis of viral proteins. see also RETROVIRUSES.

VIRUS CLASSIFICATION If viruses are indeed mobile genetic elements that have received "autonomy" (independence) from the genetic apparatus of their hosts (different types of cells), then different groups of viruses (with different genome, structure and replication) should have arisen independently of each other. Therefore, it is impossible to build for all viruses a single pedigree linking them on the basis of evolutionary relationships. The principles of "natural" classification used in animal taxonomy are not suitable for viruses.

Nevertheless, a virus classification system is necessary in practice, and attempts to create it have been made repeatedly. The most productive approach turned out to be based on the structural and functional characteristics of viruses: in order to distinguish different groups of viruses from each other, they describe the type of their nucleic acid (DNA or RNA, each of which can be single-stranded or double-stranded), its size (the number of nucleotides in the nucleic acid chain). acids), the number of nucleic acid molecules in one virion, the geometry of the virion and structural features of the capsid and the outer shell of the virion, the type of host (plants, bacteria, insects, mammals, etc.), the characteristics of the pathology caused by viruses (symptoms and nature of the disease), antigenic properties of viral proteins and features of the reaction of the body's immune system to the introduction of the virus.

For many viruses, such as measles, herpes and partly influenza, humans are the main natural reservoir. The transmission of these viruses occurs by airborne droplets or by contact.

The spread of some viral diseases, like other infections, is full of surprises. For example, in groups of people living in unsanitary conditions, almost all children in early age carry polio, usually mild, and acquire immunity. If living conditions in these groups improve, children younger age polio is not usually sick, but the disease can occur at an older age, and then it is often severe.

Many viruses cannot persist in nature for a long time at a low density of dispersal of the host species. The paucity of populations of primitive hunters and collectors of plants created unfavorable conditions for the existence of some viruses; therefore, it is very likely that some human viruses emerged later, with the emergence of urban and rural settlements. It is assumed that the measles virus originally existed among dogs (as the causative agent of fever), and smallpox in humans may have appeared as a result of the evolution of smallpox in cows or mice. The most recent examples of viral evolution include acquired immunodeficiency syndrome (AIDS). There is evidence of genetic similarities between human immunodeficiency viruses and African green monkeys.

"New" infections are usually severe, often fatal, but during the evolution of the pathogen they can become lighter. A good example is the history of myxomatosis virus. In 1950, this virus, endemic to South America and quite harmless for local rabbits, was introduced to Australia along with European breeds of these animals. The disease in Australian rabbits, previously not met with this virus, was fatal in 99.5% of cases. Several years later, the mortality from this disease decreased significantly, in some areas up to 50%, which is explained not only by "attenuating" (weakening) mutations in the viral genome, but also by the increased genetic resistance of rabbits to the disease, and in both cases, effective natural selection occurred under powerful pressure of natural selection.

The reproduction of viruses in nature is supported by different types of organisms: bacteria, fungi, protozoa, plants, animals. For example, insects often suffer from viruses that accumulate in their cells in the form of large crystals. Plants are often affected by small and simply arranged RNA viruses. These viruses do not even have special mechanisms to enter the cell. They are carried by insects (which feed on cell sap), roundworms and by contact, infecting the plant if it is mechanically damaged. Bacterial viruses (bacteriophages) have the most complex mechanism for delivering their genetic material to a sensitive bacterial cell. First, the "tail" of the phage, which looks like a thin tube, attaches to the wall of the bacterium. Then special enzymes of the "tail" dissolve a section of the bacterial wall and the phage genetic material (usually DNA) is injected into the resulting hole through the "tail", like through a syringe needle.

More than ten major groups of viruses are pathogenic for humans. Among the DNA viruses, this is the family of poxviruses (causing smallpox, vaccinia and other smallpox infections), herpes viruses (herpes sores on the lips, chickenpox), adenoviruses (diseases respiratory tract and eyes), the papovavirus family (warts and other skin growths), hepadnaviruses (hepatitis

B ). There are much more RNA-containing viruses that are pathogenic for humans. Picornaviruses (from lat. pico - very small, English.RNA - RNA) - the smallest mammalian viruses, similar to some plant viruses; they cause poliomyelitis, hepatitis A, acute colds... Mixoviruses and paramyxoviruses are the cause of various forms of influenza, measles and mumps (mumps). Arboviruses (from the English.arthropod borne - "carried by arthropods") - the largest group of viruses (more than 300) - carried by insects and are the causative agents of tick-borne and Japanese encephalitis, yellow fever, equine meningoencephalitis, Colorado tick-borne fever, Scottish sheep encephalitis and other dangerous diseases. Reoviruses, which are rather rare causative agents of respiratory and intestinal diseases in humans, have become the subject of special scientific interest due to the fact that their genetic material is represented by double-stranded fragmented RNA. see also VENERAL DISEASES; CHICKENPOX; HEPATITIS; FLU; DENGE FEVER; MONONUCLEOSIS INFECTIOUS; MEASLES; RUBELLA; MENINGITIS; NATURAL POISK; POLIO; RESPIRATORY VIRAL DISEASES; PIGGY; SYNDROME OF ACQUIRED IMMUNODEFICIENCY (AIDS); ENCEPHALITIS.

The causative agents of some diseases, including very serious ones, do not fit into any of the above categories. Until recently, for example, Creutzfeldt-Jakob disease and Kuru, degenerative diseases of the brain with a very long incubation period, were referred to a special group of slow viral infections. However, it turned out that they are not caused by viruses, but by the smallest infectious agents of a protein nature - prions ( cm... PRION).

Treatment and prevention. The reproduction of viruses is closely intertwined with the mechanisms of the synthesis of protein and nucleic acids of the cell in the infected organism. Therefore, creating drugs that selectively suppress the virus, but do not harm the body, is an extremely difficult task. Nevertheless, it turned out that in the largest herpes and smallpox viruses, genomic DNAs encode a large number of enzymes that differ in properties from similar cellular enzymes, and this served as the basis for the development of antiviral drugs. Indeed, several drugs have been created whose mechanism of action is based on suppressing the synthesis of viral DNA. Some compounds that are too toxic for general use (intravenously or by mouth) are suitable for topical use, such as for eye infections with the herpes virus.

It is known that the human body produces special proteins - interferons. They suppress the translation of viral nucleic acids and thus inhibit the reproduction of the virus. Thanks to genetic engineering, interferons produced by bacteria have become available and are being tested in medical practice (cm.GENETIC ENGINEERING) .

The most effective elements of the body's natural defenses include specific antibodies (special proteins produced by the immune system), which interact with the corresponding virus and thereby effectively prevent the development of the disease; however, they cannot neutralize a virus that has already entered the cell. An example is herpes infection: The herpes virus persists in the cells of the nerve nodes (ganglia) where antibodies cannot reach it. From time to time, the virus is activated and causes relapses of the disease.

Usually, specific antibodies are formed in the body as a result of the penetration of the infectious agent. The body can be helped by artificially boosting the production of antibodies, including building immunity in advance, through vaccination. It was in this way, through mass vaccination, that the smallpox disease was practically eliminated all over the world. see also VACCINATION AND IMMUNIZATION.

Modern methods of vaccination and immunization are divided into three main groups. Firstly, this is the use of a weakened virus strain, which stimulates the production of antibodies in the body that are effective against a more pathogenic strain. Secondly, the introduction of a killed virus (for example, inactivated with formalin), which also induces the formation of antibodies. The third option is the so-called. "Passive" immunization, i.e. introduction of ready-made "foreign" antibodies. An animal, such as a horse, is immunized, then antibodies are isolated from its blood, purified and used for administration to a patient to create immediate but short-term immunity. Sometimes antibodies are used from the blood of a person who has had the disease (for example, measles, tick-borne encephalitis).

Accumulation of viruses. To prepare vaccines, it is necessary to accumulate the virus. For this purpose, developing chicken embryos are often used, which are infected with this virus. After incubating the infected embryos for a certain time, the virus accumulated in them due to reproduction is collected, purified (by centrifugation or in another way) and, if necessary, inactivated. It is very important to remove all ballast impurities from the preparations of the virus that can cause serious complications during vaccination. Of course, it is equally important to make sure that no non-inactivated pathogenic virus remains in the preparations. In recent years, various types of cell cultures have been widely used for the accumulation of viruses. METHODS FOR STUDYING VIRUSES Bacterial viruses were the first to become the object of detailed studies as the most convenient model that has a number of advantages over other viruses. Full cycle of phage replication, i.e. the time from infection of a bacterial cell to the release of multiplied viral particles from it occurs within one hour. Other viruses usually accumulate over several days or even longer. Shortly before the Secondworld War II and soon after its end, methods were developed for studying individual viral particles. Plates with nutrient agar, on which a monolayer (solid layer) of bacterial cells has been grown, are infected with phage particles using its serial dilutions. Reproducing, the virus kills the "sheltered" cell and penetrates into neighboring cells, which also die after the accumulation of phage offspring. The area of \u200b\u200bdead cells is visible to the naked eye as a bright spot. Such spots are called "negative colonies" or plaques. The developed method made it possible to study the offspring of individual viral particles, detect the genetic recombination of viruses and determine the genetic structure and methods of phage replication in details that previously seemed incredible.

Work with bacteriophages contributed to the expansion of the methodological arsenal in the study of animal viruses. Prior to this, studies of vertebrate viruses were carried out mainly in laboratory animals; such experiments were very laborious, expensive, and not very informative. Subsequently, new methods appeared based on the use of tissue cultures; bacterial cells used in phage experiments were replaced with vertebrate cells. However, experiments on laboratory animals are very important for studying the mechanisms of development of viral diseases and continue to be carried out at the present time.

LITERATURE Virology... Edited by B. Fields, D. Knight, vol. 1–3, M., 1989

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Infection with a viral infection such as HIV can occur through blood or through sexual contact. Only after three to five years, the patient begins to worry about such symptoms of this infection as malaise, weakness, night sweats, debilitating diarrhea, fever, weight loss and some others.

The child is worried headache, watery eyes, muscle pain, throat pain, nasal congestion, hoarseness, general malaise. Subsequently, a dry and painful cough may occur, which brings the baby a lot of discomfort and pain.

Unlike other forms of life, this form does not have a cellular structure. The virus carries hereditary information that is stored in the DNA or RNA molecule, the top of the molecule is covered with a protein coat.

If you go to the pharmacy for antiviral medicationYou need to know that all medicines used to treat viruses fall into three categories ..

It is important to note that a living organism can be infected with several viruses at once. Most of these infections have some kind of affinity for a particular organ. For example, hepatitis viruses multiply primarily in liver cells.

There are a very large number of the most different types such infections. They lead to various viral diseases. In this article, we will talk about viruses that, getting into the body of children, develop in them various diseases inherent in a given age. These viral diseases are called children's, because most often it is children who get sick with them.

To combat this kind of disease, there are a huge number of drugs, which basically do not have a precisely directed action, and getting into the body kill all the useful flora in it, which often leads to dire consequences. Ideally, of course, it is best to prevent the development of the virus in your body by keeping it at a good level with the help of Bad Tiens.
In case you are sick and take medicines, then it is worth in parallel to carry out prevention with the help of Bad Tyansha to smooth out the harmful effects, side effects medications and maintaining immunity.

Viruses (Latin virus - poison) Is a non-cellular life form that is autonomous genetic structures capable of multiplying in the cells of plants and animals that are sensitive to them.

Viruses are widespread in nature and can cause various diseases of plants, animals and humans.

In outline, virus is a nucleic acid molecule (DNA or RNA) surrounded by a special envelope. Some infections of this type also include enzymes involved in the regulation of the life cycle of the virus. Penetrating into the cells of another organism, this autonomous organism releases its genetic material, which, using the resources of the infected cell, begins to form new viral particles.

In addition to viruses, there are several other non-cellular life forms in nature, such as viroids, virusoids and prions. Viroids are small circular RNA molecules (ribonucleic acid), not surrounded by a membrane, and causing various plant diseases. Virioids are also circular RNA molecules without a protein coat, which, unlike viroids, are not capable of infecting cells of other organisms only in the presence of a helper virus.

Prions are a group of pathogenic protein molecules that can cause various diseases in animals and humans, for example, Jacob-Creutzfeldt disease (mad cow disease), Kuru disease, etc.

Despite the rather simple organic structure, these microorganisms are full representatives of living nature. They are characterized by the main features of life, such as: the ability to reproduce itself, variability, heredity, the ability to adapt to environmental conditions, obedience to the laws of evolution, a certain place in the hierarchy of living organisms.

The structure of viruses
In the structure of all these microorganisms, two main components can be distinguished: nucleic acid - the carrier of genetic information and the shell.

Genetic apparatus of viruses... In nature, nucleic acids are the carrier of genetic information. There are two main types of nucleic acids known: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). In most living organisms, nucleic acids are contained in the nucleus and cytoplasm (cell sap). The described microorganisms, although they are non-cellular structures, also contain nucleic acids. By the type of nucleic acid contained, viruses are divided into two classes: DNA-containing and RNA-containing. DNA-containing viruses include hepatitis B viruses, herpes, etc. RNA-containing microorganisms are represented by influenza and parainfluenza, human immunodeficiency virus (HIV), hepatitis A, etc. In these microorganisms, as well as in other living organisms, nucleic acids play the role of the carrier of genetic information. Information about the structure of various proteins (genetic information) is encoded in the structure of nucleic acids in the form of specific sequences of nucleotides (constituents of DNA and RNA). Viral nucleic acid genes encode a variety of enzymes and structural proteins. DNA and RNA of viruses are the material substrate of heredity and variability of these microorganisms - the two main components in the evolution of viruses in particular and of all living nature in general.

Virus envelope... The genetic material of such a mature microorganism is surrounded by a special membrane. In many viruses (such as poliomyelitis), the envelope consists of protein molecules, which combine to form a spatial structure with a cavity inside, in which the nucleic acid of a given microorganism is placed. Other viruses (HIV, hepatitis B, measles, rabies), in addition to the protein coat, also have a second one, which includes proteins and fats. In its composition, this membrane is very similar to an ordinary cell membrane, since this microorganism borrows it from the host cell, but specific viral proteins that perform various functions are also embedded in it.

The virus envelope has many functions. First, it protects the fragile nucleic acid of a microorganism from destruction under the influence of adverse environmental factors. Secondly, the envelope of the virus carries various receptor proteins that recognize the target cell and help this dangerous microorganism to enter it. Thirdly, various components of the viral envelope are recognized by the host organism as antigens and stimulate the development of the immune response. Determination in blood various components a given microorganism or specific antibodies against virus proteins is an important point in the diagnosis of various viral diseases.

Using the resources of the infected cell, the virus synthesizes its own proteins and nucleic acids. In the cytoplasm (internal environment) of the host cell, the newly synthesized proteins and nucleic acids combine to form new viral particles. The mature particles are called virions. By breaking the cell membrane, they enter the intercellular environment or blood and infect new cells.

As a result of the multiplication of these microorganisms, the infected cells undergo profound changes, as a result of which the cell itself may die. In general, the destruction of cells occurs for two reasons: in one case, the cell is destroyed by the viruses themselves, and in others, it is destroyed by the body's own immune system, which recognizes and destroys infected cells. It is cell death that is the reason for the development of various clinical signs of such an infection. For example, in the case of an acute viral infection of the respiratory tract, there is a direct destruction of the epithelium of the nasopharynx, trachea and bronchi by multiplying viruses and the occurrence of symptoms such as pain, cough, mucous secretions, etc. In the case of viral hepatitis B, destruction of liver cells (hepatocytes) occurs by the cells of the human immune system, which recognize and destroy infected cells. Massive destruction of hepatocytes causes the appearance of symptoms and clinical signs such as jaundice, increased liver function tests, and in severe cases, the onset of liver failure.

Reacting to a viral infection, the body's immune system produces a number of factors (antibodies) that resist these microorganisms. The appearance of specific antibodies is observed from the end of the first week of a viral infection. By binding to viruses, antibodies cause them to be inactivated and removed from the body. This period is called the recovery phase. In some cases, after a viral infection, the body becomes protected from re-penetration of the same microorganism due to the developed immunity. Recovering from a viral infection can be complete or partial. In the case of acute viral infections, this microorganism is usually completely removed from the body. However, in some cases, a viral infection takes on a chronic course, in which the apparent clinical recovery is accompanied by the persistence of this infection in the body (hepatitis B).

It is worth noting that some viral infections can cause serious complications or death of the patient.

Bibliography:

1. Borisov LB Medical microbiology, virology, immunology, M.: Medicine, 1995
2. Korotyaev A.I. Medical Microbiology, Immunology and Virology, St. Petersburg. : SpetsLit, 2000
3. Volina E.G. Fundamentals of General Microbiology, Immunology and Virology, M.: Medicine, 2004

Viruses.

(Storage and transmission of genetic information by viruses)

COMPOSITION, SIZE AND FORM.

Schematically, viruses are hereditary material packed in a protective protein envelope, sometimes containing also lipid and carbohydrate components. In a hereditary substance - a molecule or several molecules of RNA or DNA - the "minimum consumer basket" is necessarily encoded: enzymes for copying these viral nucleic acids, as well as proteins that make up the viral particle (virion).

If in all organisms of a cellular structure, the hereditary substance is double-stranded DNA molecules, then viruses can contain not only DNA, but also RNA, and both types of nucleic acids are found in both double-stranded and single-stranded forms. Each virus has a specific form of nucleic acid. Molecules of viral RNA and DNA are unbranched (sometimes circular) polymers built from many links - nucleotides, in one such molecule - from several thousand to several hundred thousand nucleotides. Viral nucleic acids are long strands, more flexible in the case of single-stranded molecules and more elastic in the case of double-stranded ones.

There are several basic options for the "appearance" of virions. Viruses built only from nucleic acid and protein can resemble a rigid rod-shaped or flexible filamentous helix, a sphere, and also a structure that has, as it were, a head and a tail process. Lipids, if present, form an outer membrane in which some viral proteins are incorporated, and such a lipoprotein envelope envelops the protein "core" with the nucleic acid "sealed" in it.

The sizes of viral particles also vary significantly. The "thinnest" ones have a diameter of about 10 nm, and their length in the most extended reaches 2 microns. The diameter of spherical virions ranges from -20 to 300 nm. The largest known viruses are relatives of the smallpox virus, and their virions can be up to 450 nm long and 260 nm wide and thick.

DISTRIBUTION IN NATURE.

There are viruses that multiply in the cells of animals, plants, bacteria and fungi.

The structural features of the infected cell are one of the factors on which the form of the virion depends.

Some viruses have a very strict registration. For example, the polio virus can live and multiply only in cells (and even then not in all) humans and primates.

STORAGE AND TRANSFER OF GENETIC INFORMATION.

As you know, protein synthesis is carried out in ribosomes, and the amino acid sequence of the synthesized proteins is set by the messenger RNA (mRNA) molecules. When describing the variety of methods for storing and transmitting genetic information in viruses, it is convenient to designate mRNA molecules as (+) RNA.

There is a large group of viruses, the genetic material of which is mRNA. The genome of such viruses is called positive. This includes, for example, the viruses of poliomyelitis and tick-borne encephalitis, and in plants - tobacco mosaic. Once in the host cell, viral RNA provides the synthesis of its own proteins. After that, its reproduction begins. At the final stage, virions are assembled from the accumulated viral proteins and RNA.

The genome of another group of viruses is not represented by mRNA molecules, but by their complementary copy, that is, by (-) RNA molecules. Among them are influenza, measles, rabies, yellow dwarf potato viruses. The infectious process cannot begin with the synthesis of proteins recorded in a mirror form, because ribosomes do not recognize (-) RNA. But replication of viral RNA also seems impossible, since the cell does not have its own enzymes capable of carrying out this process. Viruses with a negative RNA genome solve this problem in the following way: they introduce their genome into the infected cell not in a "naked" form, as viruses of the first group do, but in the form of more complex structures containing, in particular, DNA-dependent RNA polymerase. This viral enzyme, synthesized in the previous cycle of propagation, is packaged in the virion in a form convenient for delivery to the cell. The infectious process begins with the fact that the viral enzyme copies the viral genome, forming complementary RNA molecules, that is, (+) RNA. These molecules already "find a common language" with ribosomes. Viral proteins are formed, including DNA-dependent RNA polymerase, which, on the one hand, ensures the multiplication of the viral genome in a given cell, and on the other, is "preserved for future use" in the newly formed virions.

There are viruses that form twins with negative RNA; in their genome, along with regions corresponding to (-) RNA, there are sequences of positive polarity.

In the third group of viruses, hereditary information is stored in the form of double-stranded (or ±) RNA. Together with viral RNA, the enzyme DNA-dependent RNA polymerase enters the cell, which ensures the synthesis of (+) RNA molecules. In turn, (+) RNA does two things: it provides the production of viral proteins in ribosomes and serves as a matrix for the synthesis of new chains of viral RNA polymerase. Chains of (+) and (-) RNA, combining with each other, form a double-stranded (±) RNA - a genome that is packed into a protein shell.

The fourth group is double-stranded DNA viruses. Although the genome of these viruses can be conventionally depicted as (±) DNA, in many cases there are regions in each of the two DNA strands corresponding to both positive and negative polarity.

The next group is viruses with a single-stranded DNA genome, which can be represented by molecules of both positive and negative polarity. Once in the cell, the viral genome first turns into a double-stranded form, this transformation is provided by the cellular DNA-dependent DNA polymerase.

The sixth group - retroviruses - including, in particular, such a "celebrity" as the human immunodeficiency virus (HIV). The genome of these forms is single-stranded (+) RNA, but the infectious process develops according to a completely different scenario. An unusual enzyme (revertase) is encoded in the viral genome, which has the properties of both DNA-dependent and DNA-independent DNA polymerase. This enzyme enters the infected cell along with the viral RNA and ensures the synthesis of its DNA copy, first in single-stranded form [(-) DNA], and then in double-stranded [(±) DNA]. Further events develop according to the usual schedule: synthesis of viral (+) RNA, synthesis of viral proteins, formation of virions, exit from the cell.

The seventh group is retroid viruses, of which the hepatitis B virus is best known. The composition of these viruses includes double-stranded DNA, but it replicates differently than the viruses of the fourth group. There, viral DNA is copied by DNA-dependent DNA polymerase. Here, first (+) RNA is read from the viral DNA, which then serves as a matrix for the synthesis of two components of the virion: proteins and DNA. DNA synthesis is carried out by a viral enzyme with reverse transcriptase activity according to the scheme that is implemented in retroviruses.

TYPES OF INTERACTION WITH THE CELL.

There are two main types of interaction between the virus and the cell, the fundamental difference between which is the degree of autonomy of the virus from its "host". There are compromise viruses that are more prone to obey cellular control. The genome of these virions is included in the cellular chromosome, while the viral DNA is covalently linked to the cellular one. Viral genes, as it were, are transformed into cellular ones. Further events can develop in different ways. In one case, they are almost inactive. Cells and their chromosomes divide, and together with the chromosomes, the hidden viral genome gets into each daughter cell. And under certain circumstances, the virus is activated.

In another case, new and new generations of virions are constantly produced in the infected cell, but the cell does not die.

DECODED BY THE GENE OF THE VIRUS OF ATYPICAL PNEUMONIA.

Scientists from the United States and Canada have announced a complete decoding of the genome of the virus that causes SARS. It is expected that this discovery will make it possible to conduct more accurate tests, which among many suspected diseases, it will be possible to identify with certainty the actual cases of infection. “Having this information is extremely important for faster analyzes and should certainly help us develop antibodies and vaccines,” said Julie Gerberding, director of federal center for Disease Control and Prevention in the US state of Atlanta.
The center has already performed two tests for antibodies to SARS, but they were not accurate enough for widespread use. "The discovery of the complete sequence should lead to more accurate genetic analyzes," notes Gerberding.

CONCLUSION.

Thus, it can be noted that both the internal content and form and behavior of viruses are very diverse and individual.

RNA negative viruses are much more complex. the virion contains not only RNA, but also enzymes that are capable of replicating it. The introduction into the cell not only of its own RNA, but also of RNA polymerase provides the production of many (+) RNA molecules (including mRNA), which can compete with cellular mRNA not only by skill, but also by number.

LITERATURE.

"Virology", 3 volumes / Ed. B. Fields, D. Nipe. M .: "Mir", 1989

Baturin Alexander