VIRUSES, the smallest pathogens of infectious diseases. Translated from Latin virus 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 "filtrating 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 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, there are movements of several types of genetic structures, for example, matrix, or informational, RNA (mRNA), transposons, introns, plasmids. Such mobile elements may have been the predecessors, or progenitors, of viruses.
Are viruses living organisms? In 1935, the American biochemist W. Stanley isolated the tobacco mosaic virus in crystalline form, thereby proving its molecular nature. The results obtained have sparked heated debate about the nature of viruses: are they living organisms or just activated molecules? Indeed, inside the infected cell, viruses manifest themselves as integral components of more complex living systems, but outside the cell they are metabolically inert nucleoproteins. Viruses contain genetic information, but cannot independently implement it without having their own mechanism for protein synthesis. When the features of the structure and reproduction of viruses were clarified, the question of whether they are alive gradually lost its significance.
STRUCTURE OF VIRUSES
Complete in structure and infectious, i.e. capable of causing infection, a viral particle outside the cell is called a virion. The core ("core") of the virion contains one molecule, and sometimes two or more molecules of nucleic acid. The protein sheath that covers the virion nucleic acid and protects it from harmful environmental influences is called a capsid. The virion nucleic acid is the genetic material of the virus (its genome) and is represented by deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), but never by these two compounds at once. (Chlamydia, rickettsia, and all other "truly living" microorganisms contain both DNA and RNA.) The nucleic acids of the smallest viruses contain three or four genes, while the largest viruses have up to a hundred genes.
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 "sheathless 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 individual 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 a 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.
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 viral proteins (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 cell of the host organism. 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 entity disappears: its genome becomes part of the cell's genetic apparatus and even replicates in 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). In viruses with a "-" RNA thread, the latter must first be "rewritten" into a "+" thread; 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.
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 features 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.
A group of microscopic pathogens called viroids (i.e. virus-like particles) does not quite fit into the classification system of viruses. Viroids cause many common plant diseases. These are the smallest infectious agents, devoid of even the simplest protein sheath (found in all viruses); they consist only of single-stranded RNA closed in a ring.
VIRAL DISEASES
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.
Distribution 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 poliomyelitis, usually mild, and acquire immunity. If living conditions in these groups improve, the 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 the 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, which had not previously encountered 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 took place 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 attacked 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-containing viruses, this is the family of poxviruses (causing smallpox, vaccinia and other smallpox infections), viruses of the herpes group (herpes sores on the lips, chickenpox), adenoviruses (diseases respiratory tract and eyes), the papovavirus family (warts and other growths of the skin), hepadnaviruses (hepatitis B virus). There are much more RNA-containing viruses that are pathogenic for humans. Picornaviruses (from Latin pico - very small, English RNA - RNA) are 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) - are carried by insects and are the causative agents of tick-borne and Japanese encephalitis, yellow fever, equine meningoencephalitis, Colorado tick-borne fever, Scottish encephalitis and other 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; CHICKEN POX; HEPATITIS; FLU; DENGE FEVER; MONONUCLEOSIS INFECTIOUS; MEASLES; KRASNUHA; 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. To a special group of slow viral infections more recently, for example, Creutzfeldt-Jakob disease and Kuru, degenerative diseases of the brain, with a very long incubation period, were referred to. However, it turned out that they are caused not by viruses, but by the smallest infectious agents of a protein nature - prions (see PRION).
Treatment and prevention. The reproduction of viruses is closely intertwined with the mechanisms of protein and nucleic acid synthesis 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 DNA 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 (intravenous or oral) 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 (see GENE 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 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 strain of the virus, 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, for example 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 Second World War and shortly after its end, methods were developed for studying individual viral particles. Plates with nutrient agar, on which a monolayer (continuous 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, to study the mechanisms of development of viral diseases, experiments on laboratory animals are very important and continue to be conducted at the present time.
AT THE ICOSAHEDRIC TYPE OF SYMMETRY, shown in the diagram of the structure of adenovirus, capsomeres, or protein subunits of the virus, form an isometric protein sheath, consisting of 20 regular triangles.
IN THE CASE OF A SPIRAL SYMMETRY, shown in the diagram of the structure of the tobacco mosaic virus, capsomeres, or subunits of the virus, form a spiral around the hollow tubular core.
COMBINED, or mixed, symmetry in viruses can be represented by different options. The bacteriophage particle shown in the diagram has a "head" of a regular geometric shape and a "tail" with a spiral symmetry.
Crystallization of viruses
In 1932, a young American biochemist, Wendill Stanley, was asked to study viruses. Stanley began by squeezing a bottle of juice from a ton of tobacco leaves infected with the tobacco mosaic virus. He began to study the juice using the chemical methods available to him. He exposed various fractions of the juice to various reagents, hoping to obtain a pure viral protein (Stanley was convinced that a virus is a protein). Once, Stanley received an almost pure fraction of a protein that differed in its composition from proteins of plant cells. The scientist realized that in front of him is what he so persistently sought. Stanley isolated an extraordinary protein, dissolved it in water and put the solution in the refrigerator. The next morning in a flask instead clear liquid there were beautiful silky needle-like crystals. Stanley got a tablespoon of these crystals from a ton of leaves. Then Stanley poured some crystals, dissolved them in water, moistened gauze with this water and rubbed the leaves of healthy plants with it. The plant sap has undergone a whole range of chemical influences. After such "massive processing" the viruses, most likely, should have died.
The rubbed leaves are sick. So, the strange properties of the virus were supplemented by another one - the ability to crystallize.
The crystallization effect was so overwhelming that Stanley for a long time gave up the idea that the virus is a creature. Since all enzymes are proteins, and many enzymes also increase as the body develops, and they can crystallize, Stanley concluded that viruses are pure proteins, rather enzymes.
Scientists soon became convinced that it was possible to crystallize not only the tobacco mosaic virus, but also a number of other viruses.
Five years later, English biochemists F. Bowden and N. Peary found an error in Stanley's definition. 94% of the contents of the tobacco mosaic virus consisted of protein, and 6% was nucleic acid. The virus was not actually a protein, but a nucleoprotein — a combination of protein and nucleic acid.
As soon as electron microscopes became available to biologists, scientists determined that virus crystals consist of several hundred billion particles tightly pressed together. There are so many particles in one crystal of the poliomyelitis virus that they can infect all the inhabitants of the Earth more than once. When it was possible to examine individual viral particles in an electron microscope, it turned out that they come in different shapes, but the outer shell of viruses always consists of proteins that differ in different viruses, which allows them to be recognized using immunological reactions, and the inner content is represented by nucleic acid, which is a unit of heredity.
Components of virusesThe largest viruses (smallpox viruses) approach in size to small bacteria, the smallest (causative agents of encephalitis, poliomyelitis, foot and mouth disease) - to large protein molecules. In other words, viruses have their own giants and dwarfs. (see Fig. 1) To measure viruses, a convention is used called nanometer (nm). One nm is a millionth of a millimeter. The sizes of different viruses vary from 20 to 300 nm.
So, viruses are composed of several components:
core - genetic material (DNA or RNA). The genetic apparatus of the virus carries information about several types of proteins that are required for the formation of a new virus.
a protein coat called a capsid. The envelope is often built from identical repeating subunits - capsomeres. Capsomeres form structures with a high degree of symmetry.
Additional lipoprotein membrane. It is formed from the plasma membrane of the host cell. It is found only in relatively large viruses (flu, herpes). This outer envelope is a fragment of the nuclear or cytoplasmic membrane of the host cell, from which the virus enters the extracellular environment. Sometimes in the outer shells of complex viruses, in addition to proteins, carbohydrates are contained, for example, in causative agents of influenza and herpes.
1. Additional shell
2. Capsomer (protein coat)
3. Core (DNA or RNA)
Each component of virions has certain functions: the protein coat protects them from adverse effects, nucleic acid is responsible for hereditary and infectious properties and plays a leading role in the variability of viruses, and enzymes are involved in their reproduction.
Structurally more complex viruses, in addition to proteins and nucleic acids, contain carbohydrates and lipids. Each group of viruses has its own set of proteins, fats, carbohydrates, and nucleic acids. Some viruses contain enzymes in their composition.
Unlike ordinary living cells, viruses do not consume food or produce energy. They are not able to reproduce without the participation of a living cell. The virus begins to multiply only after it enters a certain type of cell. The poliomyelitis virus, for example, can only live in the nerve cells of humans or highly organized animals such as monkey. Bacterial viruses have a slightly different structure.
Interaction of a virus with a cellViruses outside the cell are crystals, but when they enter the cell, they “come to life”. Their reproduction takes place in a special, incomparable way. First, virions enter the cell, and viral nucleic acids are released. Then the details of the future virions are "harvested". Reproduction ends with the assembly of new virions and their release into the environment.
The meeting of viruses with cells begins with its adsorption, that is, attachment to the cell wall. Then the introduction or penetration of the virion into the cell begins, which she herself carries out. However, as a rule, the penetration of the virus into the cytoplasm of the cell is preceded by its binding with a special receptor protein located on the cell surface. Binding to the receptor is carried out due to the presence of special proteins on the surface of the viral particle, which "recognize" the corresponding receptor on the surface of the sensitive cell. Dozens and even hundreds of virions can be adsorbed on one cell. The part of the cell surface to which the virus has joined is immersed in the cytoplasm and turns into a vacuole. The vacuole, the wall of which consists of a cytoplasmic membrane, can merge with other vacuoles or with the nucleus. This is how the virus is delivered to any part of the cell. This process is called viropexis.
The infectious process begins when viruses that have entered the cell begin to multiply, i.e. reduplication of the viral genome and self-assembly of the capsid occurs. For reduplication to occur, the nucleic acid must be released from the capsid. After the synthesis of a new nucleic acid molecule, it is dressed, and a capsid is formed by the viral proteins synthesized in the cytoplasm of the cell. The accumulation of viral particles leads to their exit from the cell. For some viruses, this happens by "explosion", as a result of which the integrity of the cell is violated and it dies. Other viruses are secreted in a manner similar to budding. In this case, the cells of the body can maintain their viability for a long time.
Another way of penetration into the cell in bacteriophages. Thick cell walls prevent the receptor protein, together with the attached virus, from entering the cytoplasm, as is the case when animal cells are infected. Therefore, the bacteriophage inserts a hollow rod into the cell and pushes through it the DNA (or RNA) that is in its head. The genome of the bacteriophage enters the cytoplasm, while the capsid remains outside. In the cytoplasm of the bacterial cell, the replication of the bacteriophage genome begins, the synthesis of its proteins and the formation of the capsid. After a certain period of time, the bacterial cell dies and mature phage particles are released into the environment.
It is amazing how viruses, which are tens and even hundreds of times smaller than cells, skillfully and confidently manage the cellular economy. Reproducing, they deplete cellular resources and deeply, often irreversibly, disrupt the metabolism, which ultimately causes cell death.
The form of plant viruses is generally rod-shaped and round. The dimensions of rod-shaped viruses are 300-480 x 15 nm, and those that have a rounded shape are 25-30 nm. [...]
These are microorganisms that do not have a cellular structure. The sizes of the structural units of viruses (virions) range from 10 to 300 nm. Virions include molecules of ribonucleic (RNA) or deoxyribonucleic (DNA) acids, surrounded by a protein shell. Viruses have a variety of shapes: cubic, spherical, rod-shaped, etc. The reproduction of viruses is carried out by simple division or in a more complex way only within the cells of a living organism. Viruses have specificity of action, that is, certain groups of viruses infect certain living organisms. [...]
Viruses, which are smaller and less complex than cells, cannot live independently. They are just very peculiarly packed pieces of genetic information that can live and reproduce only by infecting a cell. In this case, thousands of viral particles can form in one cell. It is assumed that viruses somehow subjugate the mechanism of cell life and use it for their own purposes. The evolutionary origins of viruses are not entirely clear. They can be considered as highly generated cells or their fragments. The genes of viruses are similar to genes of other forms and can also be mutated. [...]
This virus contains about 20% RNA, and its particles are polyhedron. The diameter of particles in electron micrographs obtained by negative contrasting is from 26 to 30 nm, which depends on the characteristics of preparation of the preparation. The detailed structure of this virus is not clear, but it is of considerable interest, since some isolates contain a satellite virus associated with this virus, described below, as well as in [...]
Another form of dependence is characteristic of the satellite virus of tobacco necrosis virus. It is the smallest known virus. Its RNA contains the amount of information sufficient to encode its own capsid protein and, possibly, a specific RIK polymorase. For other significant, but so far unknown functions, op depends on the presence of an unrelated tobacco necrosis virus. [...]
The virion of the virus is threadlike, 600-700 X 12 microns in size, inactivated at 60-67 ° C, withstands freezing. The carrier is unknown. [...]
Alfalfa mosaic virus (ALV) particles differ from other plant viruses in their bacillic form. The structure of these viruses has some features that are characteristic of both rod-shaped and isometric viruses. Five components (b0, 1a, bb, M and B) were isolated from the VML viral preparation. At least four of them were found to be necessary for the onset of infection (ch. [...]
The size and shape of microbes. The size of bacteria ranges from tenths of a micron to a few microns. On average, the body diameter of most bacteria is in the range of 0.5-1 microns, and the average length in rod-shaped bacteria is 1-5 microns. The resolution of modern bacteriological microscopes is 0.2 microns. Therefore, in order to see ultramicrobes (viruses, bacteriophages), you need to use an electron microscope that can increase the volume by a factor of millions and has a resolution of 0.4 mmq. . [...]
Single viruses of one kind or another are formations of various shapes (round, rod-shaped or other shapes), inside which there is a nucleic acid (DNA or RNA) enclosed in a protein shell (capsid). [...]
AT general view viruses are submicroscopic formations consisting of protein and nucleic acid and organized in the form of viral particles, often called viral corpuscles, virions, virospores or nucleocapsids. [...]
In some electron micrographs, they observed discoid particles of almost the same diameter as the intact virus. In these particles, a central channel was visible, the diameter of which varied, surrounded by 10 radially located subunits. [...]
Filterable forms of bacteria differ from filterable viruses in that they can also develop on artificial nutrient media. [...]
The bacteria contain 1-4% fats, 8-14% proteins and 80-85% water. The trace amounts contain phosphorus, potassium, calcium, magnesium, iron and other elements. Viruses do not have a cellular structure and have a size of 10-100 nm. [...]
The causative agent of the disease is the Beap yellow mosaic virus (Phaseolus virus 2 Smith). The virus is inactivated at a temperature of 70 ° C. It affects all leguminous plants, cannot be transmitted with seeds. [...]
The causative agents are the ara-bis mosaic virus and the raspberry ringspol virus. Both viruses belong to the same group, have isometric particles with a diameter of about: Yu im. They are transferred by contact-mechanical means, soil nematodes and grafting. On the leaves are light green or yellowish spots, of different sizes and shapes with indistinct edges. The leaves are small, deformed, the plants are depressed. In case of severe damage, plants of susceptible varieties die within a year. [...]
NOLOGY for the extraction of bacteria, viruses and chemical pollutants from water ", which consists in the fact that microorganisms passing through the cellulose sorbent" stick "into the structure of the sorbent due to electrostatic interaction." As a result, “the water becomes 100% disinfected from viruses, 100% from almost all bacteria, and 95-100% from E. coli bacteria. Impurities are removed from water in a complex way: this occurs due to the mechanical retention of particles in the porous structure of the filter material, due to molecular sorption, electrostatic interaction and ion exchange. " Personally, I don't see anything PRINCIPALLY NEW in this technology, but there is one original moment in the Life-Giving Source. I quote: "The shape of the upper part of the filter in the form of a church dome has a beneficial energetic and psychological effect on people drinking purified water." Then follows a table comparing the "Life-Giving" with all sorts of "aquaphors" and "instapurs" (sic), with which he, of course, wipes his nose. [...]
Bacteriophages and filterable viruses do not have the usual cellular structure, therefore, an organized cell is not the last unit of life. This is confirmed by the facts of the transition of visible forms of bacteria to "invisible", non-cellular forms, called filterable forms of visible bacteria. [...]
Alfalfa mosaic. The causative agent is alfalfa mosaic virus (Medicago virus 2 Smith). It is transmitted by contact-mechanical means, aphids, seeds. Symptoms: first, small rounded yellowish spots appear on the leaves, then oblong or irregular spots between lateral veins, light yellow or whitish lines along the veins. The leaves are small and deformed. In summer, symptoms are often masked. Latent infection is not uncommon. The virus has a wide range of hosts: it infects wild and cultivated plants of many families: Moths, Solanaceae, Asteraceae, Pumpkin, etc. [...]
In addition to organisms with a cellular structure, there are also non-cellular life forms - viruses and bacteriophages. By the way, viruses were discovered in 1892 by the Russian biologist D.I. Ivanov, and their name in translation means "poison", which, in general, in common use for many people reflects their impact on health. [...]
There is no clear boundary between living and nonliving substances, which is confirmed by the existence of viruses. The latter have the characteristics of both living and non-living. A generally accepted definition for them has not yet been formulated. It is usually believed that viruses are the least organized forms of life that do not have their own metabolism and can exist only inside the cells of other organisms. They do not multiply outside the cells. At the same time, the ability of viruses to reproduce, even if in contact with other cells, is a sign of living things. [...]
The soil contains various microorganisms: bacteria, actinomycetes or radiant fungi, fungi, viruses, etc. Most of them process the forest litter (humus layer), improve the soil structure, and convert organic compounds into digestible forms. With an increase in soil acidity and the formation of soluble forms of toxic metals, the activity of microorganisms, especially in the processing of forest litter, decreases. [...]
The inactivating effect of electrolysis products and chlorine is greatly influenced by the amount and form of residual chlorine (free or bound). The study of the dynamics of inactivation by electrolysis products and chlorine of the model poliomyelitis virus, Escherichia coli and Escherichia coli phage showed that in the presence of residual chlorine only in a bound state, by 30 minutes of contact, Escherichia coli died completely, and the phage virus - only by 80 and 60%, respectively. With traces of free residual chlorine, by 20 minutes of contact, E. coli and phage were inactivated by more than 99%, and the virus was inactivated only by 90%. When the content of free residual chlorine in the water is 0.1-0.3 mg / l, by 10 minutes of contact, it was completely disinfected in relation to E. coli and phage, and by 30 minutes only an insignificant amount of active viruses was detected. The difference between the degree of inactivation of the studied microorganisms was statistically significant in all cases. Under the tested conditions of disinfection with electrolysis products and chlorine of water containing microorganisms in equal concentrations, Escherichia coli was less stable than the phage, and the phage was less resistant than the virus. Therefore, E. coli and phage can serve as reliable sanitary indicators of effective water disinfection with electrolysis products and chlorine against enteroviruses. Basically, this refers to those cases when, due to unfavorable epidemic sanitary conditions, the concentration of enteroviruses in the water of reservoirs can significantly increase and reach the level of E. coli (E. L. Lovtsevich, L. A. Sergunina, 1968). [...]
So, after the invention of antibiotics, the main enemy of man was not the simplest fungi and unicellular, but viruses. There are the first symptoms that retroviruses are coming to replace viruses - pre-viral, more ancient forms of life, building their organization not on the basis of a DNA molecule, but on the basis of RNA. One of the most famous representatives of this life form is the AIDS retrovirus. [...]
Microorganisms invisible under a microscope are called ultra microbes. Of this group of ultra-microscopic forms, bacteriophages - filterable viruses and invisible forms of bacteria - are the most important in human practice. It was possible to observe ultramicrobes only in an electron microscope, which gives an increase of up to 45,000 times. Viruses (Fig. 85) are particles composed of proteins and nucleic acid (DNA or RNA). They do not have the usual cellular structure. The non-cellular form of life also includes bacteriophages (Fig. 86), which are elongated formations with a thickened end. [...]
The infectious process is a complex of reactions in a macroorganism that arise in response to the introduction and reproduction of microbes, viruses, etc. in it. It is not always accompanied by the presence of signs of the disease. For example, with microbearer or asymptomatic infection, there are no clinical signs, although its pathogen is present in the body and affects its various systems, causing the immunological restructuring of the latter. If the infectious process is accompanied by the manifestation of clinical signs, then this form of infection is called an infectious disease. Hence, an infectious disease is the so-called manifest form of infection. [...]
These viruses are characterized by similarity in morphological characteristics, reactions to electromagnetic radiation, reproduction, etc. Their main components are: C, H, N, P, O, carbohydrates and lipids. It is known that Prak-Pries and all oncoviruses are thermally unstable and are destroyed at temperatures from 50 to 70 ° C, depending on the type of oncovirus. [...]
This group includes colloidal (mineral and organomineral) particles of soils and grounds, as well as undissociated and insoluble forms of humic substances that impart color to water. The latter are washed out into natural water bodies from forest, boggy and peat soils, and are also formed in the water bodies themselves as a result of the life of aquatic plants and algae. This group can also include viruses and other organisms approaching in size to colloidal particles. Since among them there are pathogenic (pathogenic) organisms, their removal from the water is a very responsible event. [...]
The second group of impurities combines hydrophilic and hydrophobic mineral and organomineral colloidal particles of soils and grounds, undissociated and insoluble forms of high molecular weight humic substances and detergents. The kinetic stability of hydrophobic impurities is characterized by the ratio of the forces of the gravitational field and Brownian motion; their aggregate stability is due to the electrostatic state of the interface and the formation of diffuse layers or the creation of stabilizing layers on the particle surface. This group also includes viruses and other microorganisms that are similar in size to colloidal particles. [...]
Bracke's density gradient centrifugation method can be used to isolate and quantify plant viruses. As it turned out, this method is fraught with many possibilities and is currently widely used in the field of virology and molecular biology. When conducting studies by centrifugation in a density gradient, the centrifuge tube is partially filled with a solution, the density of which decreases from the bottom to the meniscus. Sucrose is most commonly used to create a gradient in the fractionation of plant viruses. Before centrifugation, virus particles can either be distributed throughout the solution volume or applied to the top of the gradient. Bracke proposed three different methods of density gradient centrifugation. With isopycpic (equilibrium) centrifugation, the process continues until all particles in the gradient reach a level where the density of the medium is equal to their own density. Thus, the fractionation of particles occurs in this case in accordance with the differences in their density. Sucrose solutions are not dense enough for isopycnic separation of many viruses. In high speed zonal centrifugation, the virus is first applied to a previously created gradient. Particles of each type are sedimented at the same time through a gradient in the form of a zone, or a strip, with a speed depending on their size, shape and density. In this case, centrifugation is terminated while the particles continue to sediment. Equilibrium zonal centrifugation is similar to high-speed zonal centrifugation, but in this case centrifugation continues until the isopycnic state is reached. The role of the density gradient in high speed centrifugation is to inhibit convection and to fix different kinds of molecules in specific zones. The theory of density gradient centrifugation is complex and not well understood. In practice, however, this is a simple and elegant method that is widely used when working with plant viruses. [...]
The main feature of the AHC CEC localized in the matrix (as well as of oncoviruses in the cell) is the presence of an interface between two media with different conductivity. In fig. 2.11 shows electron microscopy data showing adenovirus, epstein-Barr virus (EBV) and ЦЭЧ in ShchGK. Fig. 2.11 it can be seen that all formations of the same scale, have a shape close to spherical, consisting of a core and a shell, in chemical composition each shell contains electrically active ions, clearly marked boundaries for viruses and CEC with their matrices. [...]
It appears on leaves in early spring as a yellow speck. By mid-summer, this symptom disappears, but the affected leaves sometimes become wrinkled. The fruits are small, often irregular and with tubercles along the seam. Their maturation is delayed. The causative agent of the disease - Peach mosaic virus is transmitted by vaccination and budding. Plum aphid is believed to carry the virus. [...]
Despite many discoveries, there are still many blank spots in the picture of biogenesis. Only the major milestones can be considered indisputable. Thus, there is no doubt now that the emergence of the biosphere was an exceptional, single event. A tiny virus and a giant sea monster, a single-celled algae and a tree fern that disappeared millions of years ago, are all just branches and leaves on the same phylogenetic tree. Life forms always and everywhere reveal, so to speak, "blood kinship", and all her children are genetically related. From the day when the first creature appeared on Earth, life comes only from life. [...]
The cell is the basic structural and functional unit of all living organisms, an elementary living system. It can exist as a separate organism (bacteria, protozoa, some algae and fungi), and as part of the tissues of multicellular organisms. Only viruses are non-cellular life forms. [...]
According to the proposed scheme, at the first stage of the process, the formation of the enzyme-substrate complex EI of the restriction endonuclease EcoR I and double-stranded plasmid DNA occurs. The key point of the scheme is the formation of a complex E-II of the restriction endonuclease EcoR I with a circular form of DNA containing a single-stranded break, obtained as a result of hydrolysis of a phosphodiester bond in one of the DNA strands. Further, depending on the conditions (nature of the substrate, temperature, etc.) ) either the cleavage of the second DNA strand within the same E - II complex can occur with the formation of a complex of the E-III enzyme with a linear form of DNA or the dissociation of the E-P complex with the formation of a free enzyme and circular DNA containing a single-stranded break, which leads to accumulation of form II in solution. This scheme made it possible to explain the differences in the mechanisms of hydrolysis of DNA of the SV 40 virus on the one hand and DNA of ColE I and bacteriophage G4 on the other. In the case of the SV 40 virus DNA, dissociation of the E-11 enzyme-substrate complex occurs, leading to the accumulation of the circular form of DNA in solution. It was suggested that the differences in the mechanism of hydrolysis of these DNA molecules (virus SV 40; DNA ColE I and bacteriophage G4) are the result of the interaction of the EcoR I restriction enzyme with various nucleotide sequences flanking the EcoR I restriction enzyme recognition site. However, this assumption does not allow explaining the differences in the mechanism of hydrolysis of circular DNA ColE I depending on temperature (see above). [...]
The disease is known in many countries of the world. In the USSR, it was found in Ukraine, Moldova, Estonia and Georgia and is subject to internal quarantine. Plum, cherry plum, mirabelle, apricot and peach are affected. The causative agent of the disease is Plum pox (\u003d Prunus virus 7 Smith). The form of the virus is threadlike, size 760X20 named after [...]
Further development of research on the study of the mechanism of hydrolysis of plasmid DNA by restriction endonucleases received in the works of Halford et al. ... Thus, the reaction mechanism is similar to that proposed for the hydrolysis of DNA of the EU 40 virus by the restriction enzyme EcoI I. [...]
In addition to the above "general" functions, the presence of homeostasis of the body, there is another very important feature: living matter, as it were, creates another habitat, namely the possibility of settling the body with other living beings for permanent or temporary habitation. It is a new biotic habitat created by life. Many experts consider viruses to be the creatures that inhabit this environment. So, I.A. Shilov (2000) believes that the exceptional simplicity of their structure is a secondary phenomenon, even more likely it is a newly emerged form of living beings that has completely assimilated the intracellular environment in organisms of other levels. The second confirmation of this thesis is that viruses have a high degree of complexity and diversity of the genetic system. The simplification of the structure, which became possible due to the obligatory unconditional connections of viruses with the host-organism, providing stable living conditions, affected even the fundamental properties inherent in the overwhelming majority of life forms: viruses do not have irritability and lack their own protein synthesis apparatus. Viruses are not capable of independent existence, and their connection with the cell is not only a spatial, but also a rigid functional connection with which the cell and the virus represent a kind of unity. [...]
Short-term alkaline treatment of HPLC at 30 ° C and high ionic strength in situ causes breaks, leading to the formation of RNA fragments, rather uniform in size, in which s2 [...]
The number of people affected by malaria, hepatitis, HIV and many other diseases is enormous. Many physicians believe that one should not speak about "victory", but only about temporary success in the fight against these diseases. History of the fight infectious diseases is very short, and the unpredictability of changes in the environment (especially in urban) can negate these gains. For this reason, the "return" of infectious agents is recorded among viruses. Many viruses "break away" from the natural base and move to a new stage that can live in the human environment - they become causative agents of influenza, viral cancer and other diseases. Perhaps this form is HIV. [...]
The change in the weight average molecular weight and radius of rotation was judged on the basis of light scattering data. For HPMC RNA, using both degradation methods, they found that the radius of rotation increased before the onset of intense degradation of the molecule, while the radius of rotation and the weight average molecular weight of TMV RNA decreased from the very beginning of this process. Strazielli et al. Explained this finding by suggesting that the RNA of HPMC exists in the form of a closed loop. However, these results can be interpreted in a different way. For example, Hazelkorn showed that TMV RNA and HPMT RNA were sedimented together under conditions of pH and ionic strength similar to those used by Strazielli et al. In contrast to this, the circular and lichgeous forms of DNA of the phage cpX174 are easily distinguishable by their sedimentation properties [1,515]. Kuyper, on the basis of sedimentation data under various conditions, suggested that isolated RNA of the cucumber mosaic virus (strain Y) can exist in two forms: an open chain and a circular structure. However, these data, as well as in the case described above, can be explained in different ways. [...]
Bacterial DNA is a high-polymeric compound consisting of a large number of nucleotides - polynucleotides with a molecular weight of about 4 million. A DNA molecule is a chain of nucleotides, where their location has a specific sequence. In the sequence of the arrangement of nitrogenous bases, the genetic information of each species is encoded. Violation of this sequence is possible with natural mutations or under the influence of mutagenic factors. In this case, the microorganism acquires or loses any property. He inherited traits change, that is, a new form of microorganism appears. In all microorganisms - prokaryotes and eukaryotes - the carriers of genetic information are nucleic acids - DNA and RNA. Only a few viruses are an exception: they have no DNA, and hereditary information is recorded or reflected only in RNA.