How viruses and molecules are connected. Biology test "Molecular genetic level
Viruses differ from inanimate matter in two properties: the ability to reproduce similar forms to themselves (multiply) and the possession of heredity and variability.
Viruses are arranged very simply. Each viral particle consists of RNA or DNA enclosed in a protein coat called capsid (Fig. 16).
2. Vital activity of viruses.
Having penetrated the cell, the virus changes the metabolism in it, directing all its activities to the production of viral nucleic acid and viral proteins. Self-assembly of viral particles from synthesized nucleic acid molecules and proteins occurs inside the cell. Until the moment of death, a huge number of viral particles have time to be synthesized in the cell. Ultimately, the cell dies, its membrane bursts, and viruses leave the host cell (Fig. 17).
Lodging in cells living organisms, viruses cause many dangerous diseases: in humans - flu, smallpox, measles, polio, mumps, rabies, AIDS and many others; in plants - mosaic disease of tobacco, tomatoes, cucumbers, leaf twisting, dwarfism, etc.; in animals - foot and mouth disease, swine and bird plague, infectious anemia of horses, etc.
Test questions for the section "Molecular level of living nature"
Each option will be asked 10 questions
each question must be answered in one complete sentence
- What elements are included in carbohydrates? Write down general formula carbohydrates.
- What carbohydrates are found in nucleic acids (DNA and RNA)?
- Write down the names of the most important disaccharides.
- Write down the names of the most important polysaccharides.
- What polysaccharides are part of the cell walls of plant and fungal cells?
- What carbohydrates are stored in plant and animal cells as reserve substances?
- Write down the general amino acid formula.
- What are the primary and secondary structures of proteins?
- What are the tertiary and quaternary structures of proteins represented by?
- What is denaturation?
- What molecules are biopolymers?
- What are enzymes?
- What is the name of the enzyme site that interacts with the substrate molecule?
- Where are the DNA molecules in the cell?
- What nitrogenous bases are included in DNA nucleotides? RNA?
- how many hydrogen bonds is formed between complementary nitrogenous bases in DNA?
- What are the functions of DNA and RNA in a cell?
- What carbohydrates are included in DNA nucleotides? RNA?
- What organic molecules, besides proteins, have catalytic activity?
- What types of RNA are distinguished in a cell?
- Where are the RNA molecules in the cell?
- What molecules do fats consist of?
- How much energy is released during fat oxidation versus carbohydrates?
- Which molecules are the guardians genetic information?
- What molecules are the main building blocks of a cell? Primary and backup energy source?
- What carbohydrate and what nitrogenous base are included in ATP?
- What amount of energy is released during the decomposition of ATP to AMP and 2 H molecules 3 PO 4?
- Why does the body need vitamins for normal metabolism?
- What nucleic acids can be found in viruses?
- List 5 human diseases caused by viruses.
Assignments of part A. Choose one correct answer from the four suggested
A1. The lowest level of organization of the living is:
1) atomic
2) cellular
3) molecular
4) organismic
A2. Among the listed substances, it is not a biological polymer:
2) glucose
3) glycogen
4) hemoglobin
A3. Inorganic substances cells are:
1) carbohydrates and fats
2) nucleic acids and water
3) proteins and fats
4) water and mineral water
A4. Cell organic matter providing storage hereditary information and its transmission to descendants, the basis of its genetic apparatus:
3) carbohydrates
4) nucleic acids
A5. Of the listed carbohydrates, the monosaccharide is:
2) starch
3) sucrose
4) fructose
A6. Lipid molecules are composed of:
1) amino acid
2) monosaccharides
3) water and minerals
4) glycerin and higher fatty acids
A7. Compared to the oxidation of 1 g of carbon, the oxidation of fats of the same mass produces energy:
1) half as much
2) twice as much
3) four times more
4) the same amount
A8. Organic substances, which are the main building material of cell structures and take part in the regulation of the processes of its vital activity, are:
1) proteins
3) carbohydrates
4) nucleic acids
A9. The whole variety of proteins is formed due to the various combinations in their molecules:
1) 4 amino acids
2) 20 amino acids
3) 28 amino acids
4) 56 amino acids
A10. The highest level of spatial structural configuration of the hemoglobin molecule:
1) primary
2) secondary
3) tertiary
4) quaternary
A11. Monomers of nucleic acid molecules are:
1) nucleotides
2) monosaccharides
3) amino acids
4) higher fatty acids
A12. The DNA contains sugar:
2) glucose
3) fructose
4) deoxyribose
A13. Indicate a pair of complementary nucleotides in a DNA molecule:
2) AT
A14. For the DNA site ACCGTAATG, indicate the complementary strand:
1) AAGGTSAGT
2) THGTSTAACTS
3) TCTSGTTATSG
4) TGGZATTATS
A15. ATP includes:
1) ribose, adenine, three phosphoric acid residues
2) ribose, adenine, one phosphoric acid residue
3) ribose, deoxyribose, three phosphoric acid residues
4) deoxyribose, adenine, three phosphoric acid residues
A16. ATP plays an important role in the metabolism of organisms because:
1) is the structural basis of nucleotides
2) contains microenergy communication
3) is usually the end product of metabolism
4) it can be quickly obtained from the environment surrounding the body
A17. Vitamins are water-soluble:
2) C
A18. By chemical composition most enzymes are:
2) proteins
3) carbohydrates
4) nucleic acids
2) viruses
3) bacteria
4) unicellular plants
A20. Viruses are composed of:
1) cellulose membrane, cytoplasm, nucleus
2) protein membrane and cytoplasm
3) nucleic acid and protein coat
4) several microscopic cells
Assignments for part B. Choose three correct answers from the six proposed
IN 1. The DNA molecule differs from mRNA in that:
1) it is coiled
2) consists of two polynucleotide chains
3) consists of one polynucleotide chain
4) has the ability to self-double
5) does not have the ability to self-double
6) serves as a matrix for the assembly of the polypeptide chain
IN 2. Carbohydrates have the following functions:
1) signal
2) structural
3) transport
4) regulatory
5) energy
6) enzymatic
Match the content of the first and second columns
AT 3. Correlate organic matter and the function it performs in the cell and / or in the body
a b v G d 5 1 4 2 3
Establish the correct sequence of biological processes, phenomena, practical actions
AT 4. Establish the sequence of the formation of the structure of the hemoglobin protein molecule
a) twisting of protein molecules into a spiral
b) the formation of peptide bonds between amino acids and the formation of a peptide chain
c) combining several globules
d) twisting the protein molecule into a ball
<Бактериофаг>
Viruses infecting other viruses (satellite viruses.
Many viruses cause diseases such as AIDS, measles rubella, mumps (mumps), chickenpox and smallpox. Viruses are microscopic in size, many of them are able to pass through any filter. And unlike bacteria, viruses cannot be grown on nutrient media, since they do not exhibit the properties of living things outside the body. Outside a living organism (host), viruses are crystals of substances that do not have any properties of living systems.
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 the viral nature of cancer - Rous sarcoma (only in 1966, 55 years later, he was awarded the Nobel Prize in Physiology or Medicine for this discovery). 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 evidence of the role of DNA in the transmission of hereditary properties. V different years at least six more Nobel Prizes in Physiology or Medicine and three Nobel Prizes in Chemistry have been awarded for research directly related to the study of viruses. In 2002, the first synthetic virus (polio virus) was created at New York University.
The structure of viruses
Simply organized viruses consist of a nucleic acid and several proteins that form an envelope around it - a 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. Mature viral particles are called virions. In fact, they are a genome covered with a protein coat on top. This shell is a capsid. It is built of protein molecules that protect the genetic material of the virus from the effects of nucleases - enzymes that destroy nucleic acids. In some viruses, a supercapsid envelope is located on top of the capsid, also built from protein. The genetic material is nucleic acid. In some viruses, this is DNA (the so-called DNA viruses), in others - RNA (RNA viruses). RNA viruses are also called retroviruses, since for the synthesis of viral proteins in this case, reverse transcription is required, which is carried out by an enzyme - reverse transcriptase (reverse transcriptase) and is a DNA synthesis based on RNA.
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 number: 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 - about 4 × 1030, and the number of viruses (bacteriophages) in bottom sediments of the ocean practically does not depend on the depth and is very high everywhere. Hundreds of thousands of species (strains) of viruses live in the ocean, 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).
The position of viruses in the system of the organic world
Origin of viruses
Structure
Viral particles (virions) are a protein capsule - a capsid containing the genome of the virus, represented by one or more DNA or RNA molecules. The capsid is built from capsomeres - protein complexes, which, in turn, consist of protomers. Nucleic acid in complex with proteins is referred to as nucleocapsid. Some viruses also have an outer lipid membrane. The sizes of various viruses range from 20 (parvoviruses) to 500 (mimiviruses) and more nanometers. Virions often have the correct 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 more species, which allows the virus to save space in the genome.
Infection mechanism
Conventionally, the process of viral infection on the scale of one cell can be divided into several overlapping stages:
1. 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. 2. Penetration into the cage. At the next stage, the virus needs to deliver its genetic information inside the cell. Some viruses also carry their own proteins that are necessary for its implementation (this is especially true for viruses containing negative RNA). Different viruses use different strategies to enter the cell: for example, picornaviruses inject their RNA through the plasma membrane, and the virions of orthomyxoviruses are captured by the cell during endocytosis, enter the acidic environment of lysosomes, where their final maturation occurs (deproteinization of the viral particle), after which the RNA into complex with viral proteins crosses the lysosomal membrane and enters the cytoplasm. Viruses also differ in the localization of their replication, some viruses (for example, the same picornaviruses) multiply in the cytoplasm of the cell, and some (for example, orthomyxoviruses) in its nucleus. 3. Cell reprogramming. When infected with a virus, special antiviral defense mechanisms are activated in the cell. Infected cells begin to synthesize signaling molecules - interferons, which transfer the surrounding healthy cells into an antiviral state and activate immune systems. The damage caused by the multiplication of the virus in the cell can be detected by the systems of internal cellular control, and such a cell would have to "commit suicide" in a process called apoptosis or programmed cell death. Its survival directly depends on the ability of the virus to overcome the antiviral defense systems. It is not surprising that many viruses (for example, picornaviruses, flaviviruses) in the course of evolution acquired the ability to suppress the synthesis of interferons, the apoptosis program, and so on. In addition to suppressing antiviral defense, viruses strive to create the most favorable conditions in the cell for the development of their offspring. 4. Persistence. Some viruses can go into a latent state, weakly interfering with the processes occurring in the cell, and are activated only under certain conditions. This is how, for example, the strategy of reproduction of some bacteriophages is built - as long as the infected cell is in a favorable environment, the phage does not kill it, is inherited by daughter cells and often integrates into the cellular genome. However, when a bacterium infected with a lysogenic phage enters an unfavorable environment, the pathogen seizes control over cellular processes so that the cell begins to produce materials from which new phages are built. The cell becomes a factory capable of producing many thousands of phages. When mature particles leave the cell, they rupture the cell membrane, thereby killing the cell. Some cancers are associated with the persistence of viruses (for example, papovaviruses). 5. Maturation of virions and exit from the cell. Eventually, the newly synthesized genomic RNA or DNA is dressed up with the appropriate proteins and leaves the cell. It should be said that actively multiplying virus does not always kill the host cell. In some cases (for example, orthomyxoviruses) daughter viruses bud off from the plasma membrane without causing it to rupture. Thus, the cell can continue to live and produce the virus.
Remember!
How are viruses different from all other living things?
Why does the existence of viruses not contradict the basic provisions of the cell theory?
Consist of organic matter as cells (proteins, nucleic acids)
Reproduce with the help of cells
What viral diseases do you know?
Influenza, HIV, rabies, rubella, smallpox, herpes, hepatitis, measles, papilloma, poliomyelitis.
Review questions and assignments
1. How do viruses work?
Viruses are very simple in structure. Each virus is made up of nucleic acid (or DNA or RNA) and protein. Nucleic acid is the genetic material of the virus. It is surrounded by a protective protein shell - the capsid. The capsid may also contain its own viral enzymes. Some viruses, such as influenza and HIV, have an extra envelope that is formed from cell membrane host cells. The capsid of the virus, consisting of many protein molecules, possesses high degree symmetry, usually having a spiral or polyhedral shape. This structural feature allows individual proteins of the virus to combine into a complete viral particle by self-assembly.
2. What is the principle of interaction between the virus and the cell?
3. Describe the process of penetration of the virus into the cell.
"Naked" viruses enter the cell by endocytosis - the immersion of a section of the cell membrane in the place of their adsorption. Otherwise, this process is known as viropexis [virus + Greek. pexis, attachment]. "Dressed" viruses enter the cell by fusing the supercapsid with the cell membrane with the participation of specific F-proteins (fusion proteins). Acidic pH values promote fusion of the viral envelope and cell membrane. When "naked" viruses penetrate into the cell, vacuoles (endosomes) are formed. After the penetration of "dressed" viruses into the cytoplasm, there is a partial deproteinization of virions and modification of their nucleoprotein (stripping). The modified particles lose their infectious properties; in some cases, the sensitivity to RNase, which neutralizes the action of antibodies (AT), and other signs specific to certain groups of viruses change.
4. What is the effect of viruses on a cell?
Think! Remember!
1. Explain why a virus can manifest the properties of a living organism only when it invades a living cell.
The virus is a non-cellular form of life, it does not have any organelles that perform certain functions in the cells, there is no metabolism, viruses do not feed, do not multiply on their own, do not synthesize any substances. They have only heredity in the form of a single nucleic acid, DNA or RNA, as well as a capsid of proteins. Therefore, only in the host cell, when the virus inserts its DNA (if it is a retro virus, then first reverse transcription occurs and is built according to RNA-DNA) into the cell's DNA, new viruses can form. During replication and further synthesis of nucleic acids and proteins by the cell, all the information of the virus introduced by it is reproduced at the same time, and new viral particles are collected.
2. Why do viral diseases have the character of epidemics? Describe the measures to combat viral infections.
They spread quickly, by airborne droplets.
3. Express your opinion about the time when viruses appeared on Earth in the historical past, given that viruses can reproduce only in living cells.
4. Explain why in the middle of XX century. viruses have become one of the main objects of experimental genetic research.
Viruses multiply rapidly, they are easy to get infected, cause epidemics and pandemics, can serve as mutagens for humans, animals and plants.
5. What difficulties arise when trying to create a vaccine against HIV infection?
Since HIV destroys the human immune system, and the vaccine is made from weakened or killed microorganisms, their metabolic products, or from their antigens obtained by genetic engineering or chemical means. The immune system cannot withstand this action.
6. Explain why the transfer of genetic material by viruses from one organism to another is called horizontal transfer. What, then, in your opinion, is the transfer of genes from parents to children called?
Horizontal gene transfer (LGT) is a process in which an organism transfers genetic material to another organism that is not a descendant of it. Vertical gene transfer is the transfer of genetic information from a cell or organism to its offspring using conventional genetic mechanisms.
7. Over the years, at least seven Nobel Prizes in Physiology or Medicine and three Nobel Prizes in Chemistry were awarded for research directly related to the study of viruses. Using additional literature and Internet resources, prepare a report or presentation about modern achievements in the field of virus research.
Humanity's fight against the AIDS epidemic continues. And although it is too early to summarize, certain, no doubt, optimistic tendencies, everything can be traced. So, biologists from America managed to grow immune cells in which the human immunodeficiency virus cannot multiply. This was achieved with the help of the latest technique, which makes it possible to influence the work of the hereditary apparatus of the cell. University of Colorado professor Ramesh Akkina and his colleagues have designed special molecules that block the work of one of the key genes of the immunodeficiency virus. Then scientists made an artificial gene capable of synthesizing such molecules, and with the help of a carrier virus introduced it into the nuclei of stem cells, which later give rise to immune cells already protected from HIV infection. However, only clinical trials will show how effective this technique will be in the fight against AIDS.
Even 20 years ago, the disease was considered incurable. In the 90s, only short-lived interferon-alpha preparations were used. The effectiveness of this treatment was very low. Over the past decade, the "gold standard" in the treatment of chronic hepatitis C has been combined antiviral therapy with pegylated interferon-alpha and ribavirin, which is generally 60-70% effective in eliminating the virus, that is, curing hepatitis C. Moreover, among patients infected with genotypes 2 and 3 of the virus, it is about 90%. At the same time, the cure rate in patients infected with the C virus genotype, until recently, was only 40-50%.
1. Features of life (size)
2. Scheme of the structure of the virus
3. Scheme of penetration into the cell, reproduction
4. Poems and riddles about viruses
4 riddles and poems
I look sad -
My head hurts in the morning
I sneeze, I'm hoarse.
What?
It's ... the flu
Dastardly virus this flu
The head hurts now
The temperature has risen
And you need a feather potion
Baby got measles?
It's not grief at all
The doctor will help, hurry
Our baby will heal
I'm going for vaccination
I'll come proudly to the doctor
Give a syringe and an injection
All is ready? I went
Your future profession
1. Prove that basic knowledge of the processes occurring on the molecular and cellular levels organizations of living things are necessary not only for biologists, but also for specialists in other fields of natural sciences.
Biophysicists, biochemists, cannot do without such knowledge. Physical and chemical processes follow the same laws.
2. What are the professions in modern society require knowledge of the structure and characteristics of the life of prokaryotic organisms? Prepare a short (no more than 7-10 sentences) message about the profession that impressed you the most. Explain your choice.
Systemic biotechnologist. Specialist in replacing outdated solutions in various industries with new products from the biotechnology industry. For example, it will help transport companies switch to biofuels instead of diesel, and construction companies - to new biomaterials instead of cement and concrete. Use biotechnology to purify liquid media.
3. “These specialists are needed in veterinary and medical research institutes, academic institutes, in enterprises related to biotechnology. They will not be left without work in the laboratories of clinics and hospitals, at agronomic breeding stations, in veterinary laboratories and hospitals. Sometimes they are the ones who can make the most reliable and accurate diagnosis. Their research is indispensable for the early diagnosis of oncological diseases. " Imagine what kind of people you are talking about in these sentences. Prove your point.
Probably genetics. Dealing with genetic material, they can work in any industry related to living organisms, be it breeding or any branch of medical knowledge.
Viruses - a creature or a substance?
Over the past 100 years, scientists have repeatedly changed their understanding of the nature of viruses, microscopic carriers of diseases.
At first, viruses were considered toxic substances, then - one of the forms of life, then - biochemical compounds. Today it is assumed that they exist between the living and inanimate worlds and are the main participants in evolution.
V late XIX century it has been found that some diseases, including rabies and foot and mouth disease, cause particles similar to bacteria, but much smaller. Since they were biological in nature and were transmitted from one victim to another, causing the same symptoms, viruses began to be considered as the smallest living organisms that carry genetic information.
The reduction of viruses to the level of lifeless chemical objects occurred after 1935, when Wendell Stanley first crystallized the tobacco mosaic virus. It was found that crystals consist of complex biochemical components and do not possess the property necessary for biological systems - metabolic activity. In 1946, the scientist received the Nobel Prize for this work in chemistry, and not in physiology or medicine.
Stanley's further research clearly showed that any virus consists of nucleic acid (DNA or RNA) packed in a protein coat. In addition to protective proteins, some of them have specific viral proteins involved in cell infection. If we judge about viruses only by this description, then they really look more like chemical substances than a living organism. But when the virus enters the cell (after which it is called the host cell), the picture changes. He sheds the protein coat and subjugates the entire cellular apparatus, forcing him to synthesize viral DNA or RNA and viral proteins in accordance with the instructions written in his genome e. Then the virus self-assembles from these components and a new viral particle appears, ready to infect other cells.
This scheme has forced many scientists to look at viruses in a new way. They began to be considered as objects located on the border between the living and inanimate worlds. According to virologists M.H.V. van Regenmortel of the University of Strasbourg in France and B.W. Mahy of the Centers for Disease Prevention and Control, this way of living can be called a "life on loan." An interesting fact is that despite the fact that for a long time biologists viewed the virus as a "protein box" filled with chemical details, they used its ability to replicate in the host cell to study the mechanism of protein coding. Modern molecular biology owes much of its success to information obtained from the study of viruses.
Scientists have crystallized most of the cellular components (ribosomes, mitochondria, membrane structures, DNA, proteins) and today they view them either as "chemical machines" or as the material these machines use or produce. This view of the complex chemical structures that provide the vital activity of the cell, and has become the reason for not too much concern of molecular biologists with the status of viruses. Researchers were only interested in them as agents capable of using cells for their own purposes or serving as a source of infection. The more complex problem of the contribution of viruses to evolution remains unimportant to most scientists.
To be or not to be?
What does the word "alive" mean? Most scientists agree that in addition to the ability to reproduce themselves, living organisms must have other properties. For example, the life of any creature is always limited in time - it is born and dies. In addition, living organisms have a certain degree of autonomy in the biochemical sense e, i.e. to some extent rely on their own metabolic processes, providing them with substances and energy, which support their existence.
A stone, as well as a droplet of liquid in which metabolic processes take place, but which does not contain genetic material and is not capable of self-reproduction, is undoubtedly an inanimate object. A bacterium is a living organism, and although it consists of only one cell, it can generate energy and synthesize substances that ensure its existence and reproduction. In this context, what about the seed? Not every seed shows signs of life. However, being at rest, it contains the potential that it received from an undoubtedly living substance and which, under certain conditions, can be realized. At the same time, the seed can be irreversibly destroyed, and then the potential will remain unfulfilled. In this regard, the virus is more like a seed than a living cell: it has some capabilities that may not be realized, but there is no ability for autonomous existence.
You can also consider the living and as a state into which, under certain conditions, a system passes, consisting of inanimate components with certain properties. Life and consciousness can be cited as an example of such complex (emergent) systems. To achieve the appropriate status, they must have a certain level of difficulty. Thus, a neuron (by itself or even as part of a neural network) does not possess consciousness; this requires a brain. But an intact brain can be alive in the biological sense and at the same time not provide consciousness. In the same way, neither cellular nor viral genes or proteins in themselves serve as a living substance, and a cell devoid of a nucleus is similar to a decapitated person, since it does not have a critical level of complexity. The virus is also unable to reach this level. So life can be defined as a complex emergent state that includes the same fundamental building blocks that a virus possesses. If we follow this logic, then viruses, not being living objects in the strict sense of this word, still cannot be attributed to inert systems: they are on the border between living and inanimate.
| VIRUS REPLICATION |
Viruses and evolution
Viruses have their own, very long evolutionary history dating back to the origins of unicellular organisms. So, some viral repair systems, which ensure the excision of incorrect bases from DNA and the elimination of damage caused by oxygen radicals, etc., are found only in certain viruses and have existed unchanged for billions of years.
Researchers do not deny that viruses played a role in evolution. But, considering them to be inanimate matter, they put them on a par with factors such as climatic conditions... Such a factor affected organisms that had changing, genetically determined traits from the outside. Organisms more resistant to this influence successfully survived, multiplied and passed on their genes to the next generations.
However, in reality, viruses did not affect the genetic material of living organisms indirectly, but in the most direct way - they exchanged their DNA and RNA with it, i.e. were players in the biological field. The big surprise for doctors and evolutionary biologists was that most of the viruses turned out to be completely harmless creatures, not associated with any diseases. They quietly doze inside the host cells or use their apparatus for their unhurried reproduction without any damage to the cell. Such viruses have a lot of tricks that allow them to avoid the watchful eye of the cell's immune system - for each stage of the immune response they have a gene that controls this stage or modifies it in their favor.
Moreover, in the process of cohabitation of a cell and a virus, the viral genome (DNA or RNA) "colonizes" the genome of the host cell, supplying it with more and more new genes, which eventually become an integral part of the genome of this type of organisms. Viruses have a faster and more direct effect on living organisms than external factors that select genetic variants. The large populations of viruses, coupled with their high replication rate and high mutation rate, make them the main source of genetic innovation, constantly creating new genes. Some unique gene of viral origin travels from one organism to another and contributes to the evolutionary process.
A cell whose nuclear DNA has been destroyed is a real "deceased": it is devoid of genetic material with instructions for activity. But the virus can use the remaining intact cell components and cytoplasm for its replication. He subjugates the cellular apparatus and forces it to use viral genes as a source of instructions for the synthesis of viral proteins and replication of the viral genome. The unique ability of viruses to develop in dead cells is most clearly manifested when the hosts are unicellular organisms, primarily inhabiting the oceans. (The overwhelming majority of viruses live on land. According to experts, there are no more than 1,030 virus particles in the oceans.)
Bacteria, photosynthetic cyanobacteria and algae, potential hosts of marine viruses, often die under the influence of ultraviolet radiation, which destroys their DNA. At the same time, some viruses ("guests" of organisms) include a mechanism for the synthesis of enzymes that restore the damaged molecules of the host cell and bring it back to life. For example, cyanobacteria contain an enzyme that participates in photosynthesis, and under the influence of excessive amounts of light is sometimes destroyed, which leads to cell death. And then viruses called cyanophages "turn on" the synthesis of an analogue of the bacterial photosynthetic enzyme, which is more resistant to UV radiation. If such a virus infects a newly dead cell, a photosynthetic enzyme can bring the latter back to life. Thus, the virus plays the role of a "gene resuscitator".
Excessive doses of UV radiation can lead to the death of cyanophages, but sometimes they manage to return to life using multiple repairs. Usually, several viruses are present in each host cell, and if damaged, they can assemble the viral genome in parts. Various parts of the genome are able to serve as suppliers of individual genes, which together with other genes will restore the functions of the genome in full without creating a whole virus. Viruses are the only ones of all living organisms that, like the Phoenix bird, are able to rise from the ashes.
According to the International Human a Genome Sequencing Consortium, 113 to 223 genes found in bacteria and humans are absent in well-studied organisms such as the yeast Sacharomyces cerevisiae, the Drosophila melanogaster fruit fly, and round worm Caenorhabditis elegans, which are located between the two extreme lines of living organisms. Some scientists believe that yeast, fruit fly and roundworm, which appeared after bacteria, but before vertebrates, simply lost the corresponding genes at some point in their evolutionary development. Others believe that the genes were passed on to a person by bacteria that entered his body.
Together with colleagues at the Oregon Public Health Institute for Vaccines and Gene Therapy, we suggest there was a third route: the genes were originally viral, but then colonized from two different lines of organisms, such as bacteria and vertebrates. The gene that the bacteria endowed humanity with could have been passed on to the two aforementioned lines by the virus.
Moreover, we are sure that the cell nucleus itself is of viral origin. The appearance of the nucleus (a structure that exists only in eukaryotes, including humans, and absent in prokaryotes, for example, bacteria) cannot be explained by the gradual adaptation of prokaryotic organisms to changing conditions. It could have formed on the basis of a preexisting high molecular weight viral DNA that had built itself a permanent "home" inside a prokaryotic cell. This is confirmed by the fact that the gene for DNA polymerase (an enzyme involved in DNA replication) of the T4 phage (viruses that infect bacteria are called phages) are similar in their nucleotide sequence to the genes of DNA polymerases of both eukaryotes and the viruses infecting them. In addition, Patrick Forterre of the University of Paris South, who studied enzymes involved in DNA replication, concluded that the genes that determine their synthesis in eukaryotes are of viral origin.
 |
| Blue tongue virus |
Viruses affect absolutely all forms of life on Earth, and often determine their fate. However, they also evolve. Direct evidence is the emergence of new viruses, such as the human immunodeficiency virus (HIV), which causes AIDS.
Viruses are constantly changing the boundary between the biological and biochemical worlds. The further we move in the study of the genomes of various organisms, the more we will find evidence of the presence in them of genes from a dynamic, very ancient pool. Laureate Nobel Prize In 1969, Salvador Luria spoke about the influence of viruses on evolution: “It is possible that viruses, with their ability to enter and leave the cellular genome, were active participants in the process of optimizing the genetic material of all living things in the course of evolution. noticed. " Regardless of which world - living or inanimate - we will refer viruses, the time has come to consider them not in isolation, but taking into account the constant connection with living organisms.
ABOUT THE AUTHOR:
Luis Villareal(Luis P. Villarreal) - Director of the Center for Virus Research at the University of California, Irvine. Received a PhD in Biological Sciences in University of California in San Diego, then worked at Stanford University in the laboratory of Nobel laureate Paul Berg. Is actively engaged in teaching activities, is currently involved in the development of programs to combat the threat of bioterrorism.
