Biology. General biology. Grade 10. Basic level Sivoglazov Vladislav Ivanovich
14. Non-cellular life form: viruses
Remember!
How are viruses different from all other living things?
Why does the existence of viruses not contradict the basic tenets of cell theory?
What do you know about viral diseases?
In 1892, the Russian botanist Dmitry Iosifovich Ivanovsky, studying the mosaic disease of tobacco plants, found that when the juice extracted from a diseased plant was passed through filters that trap bacteria, the liquid retained the ability to cause diseases in healthy plants. The causative agent of the disease was so small that its and similar structures, which were later called viruses(from lat. virus- poison), it became possible to study only after the invention of the electron microscope.
The structure of viruses. Viruses have a very simple structure (Fig. 46). Every virus is made up of a nucleic acid (or DNA or RNA) and a protein. Nucleic acid is genetic material virus. It is surrounded by a protective protein coat capsid. The capsid may also contain its own viral enzymes. Some viruses, such as influenza and HIV, have additional shell, which is formed from the cell membrane of the host cell. The capsid of the virus, which consists of many protein molecules, has a high degree of symmetry, usually having a helical or polyhedral shape. This structural feature allows individual proteins of the virus to combine into a complete viral particle by self-assembly.
Rice. 46. Viruses: structure and diversity
Rice. Fig. 47. The life cycle of viruses (A) and an electron photograph of a bacteriophage (B)
Rice. 48. Bacteriophages on the surface of the host cell (electronic photograph)
Viruses as pathogens. Viruses can infect both eukaryotic and prokaryotic cells. Viruses that infect bacteria are called bacteriophages. Viruses cause many different diseases in animals, plants, and fungi, each with its own specific host. Tobacco mosaic virus, for example, infects tobacco plants, causing the formation of characteristic spots on the leaves - these are the sites of tissue death. The smallpox virus infects only epithelial cells, and the polio virus affects the cells of the nervous tissue. Human viral diseases are also influenza, measles, rubella, hepatitis, chicken pox, rabies, herpes, AIDS and many others.
AIDS. The human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS), was first isolated in the United States in 1981. By 2000, the number of people infected with this virus had already exceeded 30 million. The disease is currently spreading very rapidly in Asia, Africa, and Central and Eastern Europe.
HIV belongs to the group retroviruses, whose genetic material is RNA (Fig. 49). Usually, the transfer of genetic information in a cell proceeds in the direction from DNA to RNA (transcription). In retroviruses, when they enter the host cell, the opposite process occurs, the so-called reverse transcription, in which DNA is synthesized based on viral RNA, which is then integrated into the host's DNA.
Rice. 49. Human immunodeficiency virus (HIV): A - virus model; B - scheme of the structure; B - electronic photography
Rice. 50. Life cycle of human immunodeficiency virus (HIV)
Consider the life cycle of the immunodeficiency virus (Fig. 50). HIV infects and destroys white blood cells, including the so-called helper lymphocytes (from the English. help- help), which provide the formation of human immunity. After penetration of HIV into the cell by endocytosis (Fig. 50, 1–3 ) viral RNA enters the cytoplasm (Fig. 50, 4 ), where on its basis, with the help of a special enzyme, viral DNA is synthesized (Fig. 50, 5 ). The latter penetrates through the pores into the cell nucleus and integrates into the host DNA (Fig. 50, 6 ). Subsequently, during cell division, along with copying of cellular DNA, copying of the embedded viral DNA occurs, as a result of which the number of infected lymphocytes increases rapidly. This process can continue for many years. After some time, the virus is activated again (Fig. 50, 7 ) and “forces” the cell to work for itself, synthesizing viral RNA and proteins (Fig. 50, 8 ), from which new viral particles are assembled that leave the host cell (Fig. 50, 9 ). The reasons why the virus becomes active after 5–6 years of latent existence are unknown. New viral particles infect still healthy lymphocytes. As a result, the immune system is destroyed, lymphocytes no longer recognize foreign proteins and pathogenic bacteria that enter the body, and the person becomes vulnerable to any infectious diseases. Every year, 1–2% of people with HIV develop AIDS. AIDS patients are susceptible to various bacterial, viral and fungal infections, which cause their death. More than 60% of AIDS patients die from pneumonia, which is usually successfully dealt with by the immune system of a healthy person. Many HIV carriers develop malignant tumors, and when infected with toxoplasmosis, the large hemispheres of the brain are affected, which can later lead to paralysis and coma.
HIV is usually transmitted through blood or semen. In 90% of cases, infection occurs through sexual contact, while the risk of infection increases in proportion to the increase in the number of sexual partners. Repeated use of the same syringe leads to the rapid spread of the virus among drug addicts. HIV can enter the human body through contact with the patient's blood, for example, when treating wounds. There is a possibility of infection through transfusion of blood that has not been tested for the presence of HIV. From an HIV-infected mother, the virus can enter the bloodstream of the fetus through the placenta or be transmitted to the newborn through breastfeeding. But airborne droplets and handshakes do not spread this virus.
HIV is a virus, so antibiotics that are used to treat bacterial infections are powerless in this case. Modern medicine is developing drugs that inhibit HIV replication, but their use has many side effects and the prospects for their use are still unclear. Developing an HIV vaccine also presents some challenges; this is due to the structural features of this virus and the severity of the disease that it causes. To date, an important direction in the treatment of AIDS is the restoration of the immune system of those infected.
While there is no effective treatment for this disease, the best way to protect against AIDS is to take precautions:
- casual sexual intercourse should be avoided, and during sexual intercourse, isolate yourself from the partner’s sperm and blood using a condom;
- in hospitals, dental clinics, clinics and beauty salons, it is necessary to use disposable syringes, and carefully sterilize reusable instruments, observing all necessary conditions;
Donated blood should be tested for the presence of antibodies to HIV.
Viruses as carriers of genetic information. There is a hypothesis that viruses are genetic material that once left the cell, but retained the ability to reproduce itself when returning to it. Consequently, in the process of evolution, viruses arose later than the appearance of the cellular form, and any viral infection should be considered as the receipt by the cell of some alien genetic information.
Many viruses are able not only to introduce their hereditary information into the host organism, but also, by integrating into the host's DNA, change the functioning of cellular genes. In the process of copying viral DNA, sometimes partial copying of the host's genetic material also occurs. In this case, newly assembled viral particles leaving the cell will carry with them a copy of some of the host's hereditary information. Thus, viruses can transfer genes between organisms of different species, orders, and even classes, the crossing of which is in principle impossible. Currently, viruses are considered not only as pathogens of infectious diseases, but also as carriers of genes between organisms.
Review questions and assignments
1. How are viruses arranged?
2. What is the principle of interaction between a virus and a cell?
3. Describe the process by which a virus enters a cell.
4. What is the effect of viruses on the cell?
5. Using knowledge about the ways of spreading viral and bacterial infections, suggest ways to prevent infectious diseases.
6. Suggest several different classifications of viruses. What criteria did you base these classifications on? Compare your classifications with the classifications your classmates have created.
Think! Execute!
1. Explain why a virus can exhibit the properties of a living organism only by invading a living cell.
2. Why are viral diseases epidemic? Describe measures to combat viral infections.
3. Express your opinion about the time of the appearance of viruses on Earth in the historical past, given that viruses can only reproduce in living cells.
4. Explain why in the middle of the XX century. viruses have become one of the main objects of experimental genetic research.
5. What difficulties arise when trying to create a vaccine against HIV infection?
6. Explain why the transfer of genetic material from one organism to another by viruses is called horizontal transfer. What then, in your opinion, is called the transfer of genes from parents to children?
7. Over the years, at least seven Nobel Prizes in Physiology or Medicine and three Nobel Prizes in Chemistry have been awarded for research directly related to the study of viruses. Using additional literature and Internet resources, prepare a report or presentation on current advances in virus research.
8. Create a portfolio on the topic "The role of viruses in the life of organisms and the evolution of the organic world on Earth."
Work with computer
Refer to the electronic application. Study the material and complete the assignments.
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Viroids. Infectious agents are found in nature much less than viruses - viroids. They consist only of a circular RNA molecule and are devoid of any shells. The smallest viroids are only 220 nucleotides long. Viroids are found in the cells of many plants. It is believed that they are cut sections of mRNA that have acquired the ability to replicate. However, they do not work like mRNAs and do not code for proteins.
Once in plant cells, viroids interfere with the work of the host cell genome and cause serious plant diseases. This is how millions of coconut palms in the Philippines died in the second half of the 20th century. Plantings of potatoes, citrus fruits, cucumbers, ornamental flowers and other wild and agricultural plants are periodically seriously affected by viroids. Viroids have not yet been found in animal cells and in humans.
Viruses and cancer. Many viruses are able, penetrating into the cells of the body, to integrate their genome into the genome of the cell, thereby causing serious disturbances in the functioning of the genetic apparatus of normal cells. As a result, a normal cell can become cancerous.
Many animals (fish, amphibians, birds, mammals) have dozens of viruses that cause cancer. Entire groups of oncoviruses have been found in humans. It is believed that about 15% of human tumors are provoked by a viral infection.
Repeat and remember!
Human
Immunity. Proteins or polysaccharides of viruses entering the body are antigens. Antigens- these are any foreign substances that, when entering the body, are perceived as genetically alien and cause an immune response. Immunity is the ability of organisms to defend themselves against pathogens, viruses and other foreign bodies and substances, thereby maintaining the constancy of their composition and properties.
There are several types of immunity. If immunity exists or arises in a person without any special effects, it is called natural. Immunity obtained through the use of medical devices is called artificial.
natural innate immunity is the same for all individuals of the species and is inherited, that is, it is genetically fixed. So, a person does not suffer from many diseases that are found in animals. For example, a person will never get sick with canine distemper, just as a dog will never get the flu.
Natural acquired immunity differs in different people and is not inherited, so it is also called individual immunity. Passive natural immunity provide antibodies received by the child from the mother along with breast milk. Active natural immunity formed after an illness. Such immunity is also called post-infection. It remains in the body for a long time. After some diseases, immunity persists for life, for example, after measles, rubella, scarlet fever and other “childhood diseases”.
artificial immunity can only be acquired. artificial active immunity formed in response to the introduction of a vaccine into the body. Vaccine- This is a preparation of weakened or killed pathogens, their fragments or toxins. With the introduction of a vaccine (vaccination), an immune response develops in the body in a weak form, as a result of which special cells are formed in the blood that are capable of synthesizing antibodies to this pathogen. Antibodies are complex proteins (immunoglobulins). They are able to bind to antigens and render them harmless. When antigen binds, an inactive antigen-antibody complex is formed, which can be destroyed by leukocytes.
Artificial active immunity is stable, lasts for years. For the first time, systematic vaccinations against smallpox began to be used from the beginning of the 19th century. after the work of the English physician Edward Jenner (1749–1823). His work was continued by the French microbiologist Louis Pasteur (1822–1895). He introduced the term "vaccine" and used vaccination in medical practice.
artificial passive immunity occurs when a drug is administered to a person serum, which already contains ready-made antibodies against the pathogen. This is especially important if the infection has already occurred. Passive immunity is unstable, persists for 4-6 weeks, during which antibodies are gradually destroyed.
Your future profession
1. Prove that basic knowledge about the processes occurring at the molecular and cellular levels of the organization of living things is necessary not only for biologists, but also for specialists in other areas of the natural sciences.
2. What 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.
3. “These specialists are needed in veterinary and medical research institutes, academic institutes, and enterprises related to biotechnology. They will not be left without work in the laboratories of polyclinics and hospitals, at agronomic breeding stations, in veterinary laboratories and hospitals. Sometimes they can make the most reliable and accurate diagnosis. Their research is indispensable for the early diagnosis of cancer.” Guess which type of people these sentences are talking about. Prove your point.
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The human body is prone to all kinds of diseases and infections; animals and plants also get sick quite often. Scientists of the last century tried to identify the cause of many diseases, but even having determined the symptoms and course of the disease, they could not confidently say about its cause. And only at the end of the nineteenth century did such a term as "viruses" appear. Biology, or rather one of its sections - microbiology, began to study new microorganisms, which, as it turned out, have long been adjacent to humans and contribute to the deterioration of his health. In order to more effectively fight viruses, a new science emerged - virology. It is she who can tell a lot of interesting things about ancient microorganisms.
Viruses (biology): what is it?
Only in the nineteenth century, scientists found that the causative agents of measles, influenza, foot-and-mouth disease and other infectious diseases, not only in humans, but also in animals and plants, are microorganisms invisible to the human eye.
After the viruses were discovered, biology was not immediately able to answer the questions posed about their structure, origin and classification. Humanity has a need for a new science - virology. IN currently virologists are working on the study of already familiar viruses, watching their mutations and inventing vaccines to protect living organisms from infection. Quite often, for the purpose of the experiment, a new strain of the virus is created, which is stored in a "sleeping" state. On its basis, drugs are being developed and observations are being made on their effects on organisms.
In modern society, virology is one of the most important sciences, and the most sought-after researcher is a virologist. The profession of a virologist, according to sociologists, is becoming more and more popular every year, which well reflects the trends of our time. After all, according to many scientists, soon wars will be waged with the help of microorganisms and ruling regimes will be established. Under such conditions, a state with highly qualified virologists may be the most resilient, and its population the most viable.
The emergence of viruses on Earth
Scientists attribute the emergence of viruses to the most ancient times on the planet. Although it is impossible to say exactly how they appeared and what form they had at that time. After all, viruses have the ability to penetrate absolutely any living organisms, they have access to the simplest forms of life, plants, fungi, animals and, of course, humans. But viruses do not leave behind any visible remains in the form of fossils, for example. All these features of the life of microorganisms significantly complicate their study.
- they were part of the DNA and separated over time;
- they were built into the genome from the very beginning and under certain circumstances "woke up", began to multiply.
Scientists suggest that in the genome of modern people there is a huge number of viruses that our ancestors were infected with, and now they have naturally integrated into DNA.
Viruses: when were they discovered
The study of viruses is a fairly new section in science, because it is believed that it appeared only at the end of the nineteenth century. In fact, it can be said that an English doctor unconsciously discovered the viruses themselves and their vaccines at the end of the nineteenth century. He worked on the creation of a cure for smallpox, which at that time mowed down hundreds of thousands of people during an epidemic. He managed to create an experimental vaccine directly from the sore of one of the girls who had smallpox. This vaccine proved to be very effective and saved more than one life.
But D.I. Ivanovsky is considered the official "father" of viruses. This Russian scientist studied diseases of tobacco plants for a long time and made an assumption about small microorganisms that pass through all known filters and cannot exist on their own.
A few years later, the Frenchman Louis Pasteur, in the process of fighting rabies, identified its pathogens and introduced the term "viruses". An interesting fact is that the microscopes of the late nineteenth century could not show viruses to scientists, so all assumptions were made regarding invisible microorganisms.
Development of virology
The middle of the last century gave a powerful impetus to the development of virology. For example, the invented electron microscope finally made it possible to see viruses and classify them.
In the fifties of the twentieth century, a polio vaccine was invented, which became a salvation from this terrible disease for millions of children around the world. In addition, scientists have learned to grow human cells in a special environment, which has led to the possibility of studying human viruses in the laboratory. At the moment, about one and a half thousand viruses have already been described, although fifty years ago only two hundred such microorganisms were known.
Properties of viruses
Viruses have a number of properties that distinguish them from other microorganisms:
- Very small sizes, measured in nanometers. Large human viruses, such as smallpox, are three hundred nanometers in size (that's only 0.3 millimeters).
- Every living organism on the planet contains two types of nucleic acids, while viruses have only one.
- Microorganisms cannot grow.
- Viruses reproduce only in the living cell of the host.
- Existence occurs only inside the cell; outside of it, the microorganism cannot show signs of vital activity.
Virus Shapes
To date, scientists can confidently declare two forms of this microorganism:
- extracellular - virion;
- intracellular - virus.
Outside the cell, the virion is in a "sleeping" state, it will not show any signs of life. Once in the human body, it finds a suitable cell and, only having penetrated into it, it begins to actively multiply, turning into a virus.
The structure of the virus
Almost all viruses, despite the fact that they are quite diverse, have the same type of structure:
- nucleic acids that make up the genome;
- protein shell (capsid);
- some microorganisms also have a membrane coating on top of the shell.
Scientists believe that this simplicity of structure allows viruses to survive and adapt in changing conditions.
Currently, virologists distinguish seven classes of microorganisms:
- 1 - consist of double-stranded DNA;
- 2 - contain single-stranded DNA;
- 3 - viruses copying their RNA;
- 4 and 5 - contain single-stranded RNA;
- 6 - transform RNA into DNA;
- 7 - transform double-stranded DNA through RNA.
Despite the fact that the classification of viruses and their study have stepped far forward, scientists admit the possibility of the emergence of new types of microorganisms that differ from all those already listed above.
Types of viral infection
The interaction of viruses with a living cell and the way out of it determines the type of infection:
- lytic
In the process of infection, all viruses simultaneously leave the cell, and as a result, it dies. In the future, viruses "settle" in new cells and continue to destroy them.
- persistent
Viruses leave the host cell gradually, they begin to infect new cells. But the former continues its vital activity and "gives birth" to more and more new viruses.
- Latent
The virus is embedded in the cell itself, in the process of its division, it is transmitted to other cells and spreads throughout the body. Viruses can remain in this state for quite a long time. Under the necessary set of circumstances, they begin to actively multiply and the infection proceeds according to the types already listed above.
Russia: where are viruses studied?
In our country, viruses have been studied for quite a long time, and it is Russian specialists who are leading in this area. The D.I. Ivanovsky Research Institute of Virology is located in Moscow, whose specialists make a significant contribution to the development of science. Research laboratories operate on the basis of the research institute, a consulting center and a department of virology are maintained.
In parallel, Russian virologists are working with WHO and expanding their collection of virus strains. Research Institute specialists work in all areas of virology:
- general:
- private;
- molecular.
It should be noted that in recent years there has been a tendency to unite the efforts of virologists around the world. Such joint work is more effective and allows serious progress in the study of the issue.
Viruses (biology as a science has confirmed this) are microorganisms that accompany all life on the planet throughout their existence. Therefore, their study is so important for the survival of many species on the planet, including humans, who have become victims of various epidemics caused by viruses more than once in history.
1. INTRODUCTION PAGE 1
2. EVOLUTIONARY ORIGIN P.2
3. PROPERTIES OF VIRUSES. NATURE OF VIRUSES. PAGE 2
4.STRUCTURE AND CLASSIFICATION OF VIRUSES P.3
5. INTERACTION OF A VIRUS WITH A CELL P.6
6. SIGNIFICANCE OF VIRUSES PAGE 7
7.VIRAL DISEASES P.9
8. FEATURES OF VIRUS EVOLUTION ON THE MODERN
STAGE. PAGE 14
9. CONCLUSION PAGE 15
10. LIST OF USED LITERATURE. PAGE 16
Introduction
By the end of the last century, no one doubted that every infectious disease causes its own microbe, which can be successfully fought.
“Just give it time,” said bacteriologists, “and soon there won’t be a single disease left.” But years passed, and the promises were not kept. People became infected with measles, foot-and-mouth disease, polio, trachoma, smallpox, yellow fever, influenza. Millions of people died of terrible diseases, and microbes - pathogens could not be found.
Finally, in 1892 Russian scientist D. I. Ivanovsky attacked the right track. Studying tobacco mosaic, a disease of tobacco leaves, he came to the conclusion that it was not caused by a microbe, but by something smaller. This “something” penetrates through the thinnest filters capable of retaining bacteria, does not multiply on artificial media, perishes when heated, and could not be seen in a light microscope. Filterable poison!
This was the conclusion of the scientist. But poison is a substance, and the causative agent of tobacco was a being. It reproduced well in the leaves of plants. The Danish botanist MartinWillem Beyrinik called this new "something" a virus, adding that the virus is a "liquid, living, contagious beginning." Translated from the Latin "virus" means "poison"
A few years later, F. Leffler and P. Frosch discovered that the causative agent of foot-and-mouth disease, a disease often found in livestock, also passes through bacterial filters. Finally, in 1917, Canadian bacteriologist F. de Erell discovered a bacteriophage, a virus that infects bacteria.
Thus, viruses of plants, animals and microorganisms were discovered. These events marked the beginning of a new science - virology that studies non-cellular forms of life.
Evolutionary origin of viruses
The nature of viruses still causes heated discussions among specialists. The reason for this is largely the numerous and often very contradictory hypotheses that have been put forward to date and, unfortunately, have not been objectively proven in any way.
More plausible, it seems hypothesis of the endogenous origin of viruses. According to it, viruses are a piece of once cellular nucleic acid that has adapted to separative replication. This version is to some extent confirmed by the existence of plasmids in bacterial cells, the behavior of which is in many respects similar to viruses. Along with this, there is also a “space” hypothesis, according to which viruses did not evolve on Earth at all, but were brought to us from the Universe by means of some cosmic bodies.
properties of viruses. Nature of viruses
2. They do not have their own metabolism, they have a very limited number of enzymes. For reproduction, the metabolism of the host cell, its enzymes and energy are used.
Viruses do not multiply on artificial nutrient media- they are too picky about food. Ordinary meat broth, which suits most bacteria, is not suitable for viruses. . They need living cells, and not any astrologically defined ones. Like other organisms, viruses are capable of replication. Viruses have heredity.. The hereditary traits of viruses can be taken into account by the spectrum of affected hosts and the symptoms of the diseases caused, as well as by the specificity of the immune responses of natural hosts or artificial immunized experimental animals. The sum of these features allows you to clearly determine the hereditary properties of any virus, and even more - its varieties that have clear genetic markers, for example: the neurotropism of some influenza viruses, etc. . Variation is the other side of heredity, and in this respect viruses are like all other organisms inhabiting our planet. At the same time, in viruses, one can observe both genetic variability associated with a change in the hereditary substance, and phenotypic variability associated with the manifestation of the same genotype in different conditions.
Structure and classification of viruses
Viruses cannot be seen with an optical microscope because they are smaller than the wavelength of light. They can only be seen with an electron microscope.
Viruses consist of the following main components :
1 . Core - genetic material (DNA or RNA) that carries information about several types of proteins necessary for the formation of a new virus.
2 . The protein shell, which is called capsid (from the Latin word capsa - box). It is often built from identical repeating subunits - capsomeres. Capsomeres form structures with a high degree of symmetry.
3 . Additional lipoprotein sheath. It is formed from the plasma membrane of the host cell and is found only in relatively large viruses (influenza, herpes).
The capsids and the additional shell have protective functions, as if protecting the nucleic acid. In addition, they contribute to the penetration of the virus into the cell. A fully formed virus is called a virion.
The schematic structure of an RNA-containing virus with a helical symmetry type and an additional lipoprotein envelope is shown on the left in Figure 2, its enlarged cross section is shown on the right.
Fig.2. Schematic structure of the virus: 1 - core (single-stranded RNA); 2 - protein shell (Capsid); 3 - additional lipoprotein shell; 4 - Capsomeres (structural parts of the Capsid).
The number of capsomeres and the way they are stacked are strictly constant for each type of virus. For example, the polio virus has 32 capsomeres, while the adenovirus has 252.
Since the basis of all living things is genetic structures, viruses are now classified according to the characteristics of their hereditary substance - nucleic acids. All viruses are divided into two large groups :DNA containing viruses(deoxyviruses) and RNA viruses(riboviruses). Then each of these groups is subdivided into viruses with double-stranded and single-stranded nucleic acids. The next criterion is the type of symmetry of the virions (depending on the way the capsomeres are stacked), the presence or absence of external shells, according to the host cells. In addition to these classifications, there are many others. For example, by the type of transmission of infection from one organism to another.
Fig.3. Schematic representation of the location of capsomeres in the capsid of viruses. The influenza virus has a spiral type of symmetry - A. Cubic type of symmetry in viruses: herpes - b, adenovirus - V, poliomyelitis - G
ENVELOPEDouble-stranded The genetic material of the virus (DNA or RNA) is surrounded by a protein shell. DNA Structure of Viruses
/>poxviruses
/>herpes - viruses
single-stranded RNA
/>viruses, measles, mumps
/>rabies viruses
/>leukemia, AIDS viruses
SHELLLESS
double stranded DNA
/>irido - viruses
/>adeno - viruses
The interaction of the virus with the cell
Viruses can live and multiply only in the cells of other organisms. Outside the cells of organisms, they do not show any signs of life. In this regard, viruses are either an extracellular resting form (varion),
or intracellular replicating - vegetative. Varions demonstrate excellent viability. In particular, they withstand pressure up to 6000 atm and tolerate high doses of radiation, but they die at high temperatures, exposure to UV rays, as well as exposure to acids and disinfectants.
The interaction of the virus with the cell go through several stages in succession:
1. First stage represents adsorption of varions on the surface of the target cell, which for this must have the appropriate surface receptors. It is with them that the viral particle specifically interacts, after which they are firmly bound, for this reason cells are not susceptible to all viruses. This explains the strict certainty of the routes of penetration of viruses. For example, receptors for the influenza virus are present on the cells of the mucous membrane of the respiratory tract, while skin cells do not have them. Therefore, it is impossible to get sick through the skin with the flu - for this you need to inhale the viral particles with air, the hepatitis A or B virus penetrates and multiplies only in the liver cells, and the mumps virus (mumps) - in the cells of the parotid salivary glands, etc.
2. Second stage consists of penetration of the whole varion or its nucleic acid into the host cell.
3.Third stage called deproteinization.In the course of it, the carrier of the genetic information of the virus, its nucleic acid, is released.
4. During fourth stage based on viral nucleic acid synthesis of compounds necessary for the virus.
5.B fifth stage going on synthesis of viral particle components- nucleic acid and capsid proteins, and all components are synthesized repeatedly.
6. During sixth stage from previously synthesized numerous copies of nucleic acids and proteins new virions are formed by self-assembly
7.Last- seventh stage- represents the release of newly assembled viral particles from the host cell. This process is different for different viruses. In some viruses, this is accompanied by cell death due to the release of lysosome lytic enzymes - cell lysis. In others, varions exit the living cell by budding, but in this case, too, the cell dies over time.
The time elapsed from the moment the virus enters the cell until the release of new varions is called latent or latency period. It can vary widely: from several hours (5-6 for smallpox and influenza viruses) to several days (measles viruses, adenoviruses, etc.).
A different way of penetration into the cell in bacterial viruses is bacteriophages .Thick cell walls do not allow the receptor protein, together with the virus attached to it, to sink into the cytoplasm, as happens when animal cells are infected. Therefore, the bacteriophage introduces a hollow the rod into the cell and pushes through it the DNA (or RNA) located in its head. The genombacteriophage enters the cytoplasm, while the capsid remains outside. into the cytoplasm bacterial cells begin reduplication of the bacteriophage genome, the synthesis of its proteins and the formation of a capsid. After a certain period of time, the bacterial cell dies, and mature phage particles enter the environment.
Bacteriophages that form a new generation of phage particles in infected cells, which leads to clisis (destruction) of the bacterial cell, are called virulent phages.
Some bacteriophages do not replicate inside the host cell. Instead, their nucleic acid is incorporated into the host's DNA, forming with it a single molecule capable of replication. Such phages are called temperate phages,or prophages. The prophage does not have a lytic effect on the host cell and replicates together with the cellular DNA during division. Prophage containing bacteria are called lysogenic. They show resistance to the phage contained in them, as well as to other phages close to it. The connection of a prophage with a bacterium is very strong, but it can be broken under the influence of inducing factors (UV - rays, ionizing radiation, chemical mutagens). It should be noted that lysigenic bacteria can change their properties (for example, release new toxins).
The meaning of viruses
Viruses of bacteria, plants, insects, animals and humans are known to science. There are more than 1000 of them in total. The processes associated with the reproduction of the virus most often, but not always, damage and destroy the host cell. Reproduction of viruses, coupled with the destruction of cells, leads to the emergence of disease states in the body. Viruses cause many human diseases: measles, mumps, influenza, polio, rabies, smallpox, yellow fever, trachoma, encephalitis, some oncological (tumor) diseases, AIDS. It is not uncommon for people to develop warts. Everyone knows how after a cold they often “brush” the lips and wings of the nose. These are also all viral diseases. Scientists have found that many viruses live in the human body, but they do not always manifest themselves. Only a weakened organism is exposed to the effects of a pathogenic virus. The ways of infection with viruses are very different: through the skin with bites of insects and ticks; through saliva, mucus and other secretions of the patient; through the air; with food; sexually and others. Droplet infection is the most common way respiratory diseases are spread. When coughing and sneezing, millions of tiny droplets of liquid (mucus and saliva) are thrown into the air. These droplets, along with the living microorganisms they contain, can be inhaled by other people, especially in crowded places. In animals, viruses cause foot-and-mouth disease, plague, and rabies; insects - polyhedrosis, granulomatosis; in plants - mosaic or other changes in the color of leaves or flowers, leaf curl and other changes in shape, dwarfism; finally, in bacteria - their decay. The idea of viruses as unstoppable "destroyers" was preserved in the study of a special group of viruses that infect bacteria. We are talking about obacteriophages. The ability of phages to destroy bacteria can be used in the treatment of some diseases caused by these bacteria. Phages really became the first group of viruses "tamed" by man. They quickly and ruthlessly dealt with their closest neighbors in the microcosm. Plague, typhoid, dysentery, cholera vibrios literally “melted” before our eyes after meeting with these viruses. They began to be used for the prevention and treatment of many infectious diseases, but, unfortunately, failures followed the first successes. This was due to the fact that phages attacked bacteria in the human body not as actively as in a test tube. In addition, the bacteria turned out to be "smarter" than their enemies: they very quickly adapted to phages and became insensitive to their action.
After the discovery of antibiotics, phages receded into the background as a medicine, but they are still successfully used to recognize bacteria. The fact is that phage are able to very accurately find "their bacteria" and quickly dissolve them. Similar properties of phages formed the basis of medical diagnostics. This is usually done as follows: the bacteria isolated from the patient's body are grown on a solid nutrient medium, after which various phages are applied to the resulting "lawn", for example, dysentery, typhoid, cholera and others. A day later, the cups are viewed in the light and it is determined which phage caused the dissolution of the bacteria. If dysentery phage had such an effect, then dysentery bacteria were isolated from the patient's body, if typhoid - typhoid bacteria.
Sometimes viruses that infect animals and insects come to the aid of a person. More than twenty years ago, the problem of the fight against wild rabbits became acute in Australia. The number of these rodents reached alarming proportions. They destroyed crops faster than locusts and became a real national disaster. Conventional methods of dealing with them proved to be ineffective. And then scientists released a special virus to fight rabbits, capable of destroying almost all infected animals. But how to spread this disease among shy and cautious rabbits? The mosquitoes helped. They played the role of "flying needles", spreading the virus from rabbit to rabbit. At the same time, mosquitoes remained completely healthy.
Other examples of the successful use of viruses to kill pests can be cited. Everyone knows the damage caused by caterpillars and sawfly beetles. The former eat the leaves of useful plants, the latter infect trees in gardens and forests. Take off the so-called polyhedrosis and granulose viruses, which are sprayed with spray guns in small areas, and aircraft are used to treat large areas. This was done in the USA (in California) when fighting caterpillars that infect alfalfa fields, and in Canada when destroying the pine sawfly. It is also promising to use viruses to combat caterpillars that infect cabbage and beets, as well as to destroy domestic moths.
What happens to a cell if it is infected with not one, but two viruses? If it was decided that in this case the disease of the cell would worsen and its death would accelerate, then they were mistaken. It turns out that the presence of one virus in a cell often reliably protects it from the destructive action of another. This phenomenon was called by scientists the interference of viruses. It is associated with the production of a special protein - interferon, which activates a protective mechanism in cells that can distinguish viral from non-viral and selectively suppress viral. Interferon suppresses reproduction in the cells of most viruses (if not all). Interferon, produced as a therapeutic drug, is now used to treat and prevent many viral diseases.
What other useful things can be expected from viruses in the future? Let's jump into the realm of speculation. First of all, it is worth recalling genetic engineering. Viruses can provide scientists with invaluable benefits by capturing the desired genes in some cells and transferring them to others. Finally, there is another possibility of using viruses. Scientists have discovered a virion that can selectively destroy some tumors in mice. Viruses that kill human tumor cells have also been obtained. If it is possible to deprive these viruses of their disease-causing properties while retaining their ability to selectively destroy malignant tumors, then in the future, perhaps, a powerful tool will be obtained to combat these serious diseases. The search for such viruses is underway, and now this work no longer seems fantastic and hopeless.
Let's briefly dwell on some viral diseases:
smallpox
smallpox is one of the oldest diseases. In the past, it was the most common and most dangerous disease. A description of smallpox was found in the Egyptian papyrus of Amenophis Ι, compiled 4000 BC. Smallpox lesions have been preserved on a kozhemumium buried in Egypt 3000 BC. In the 16th - 18th centuries in Western Europe, in some years, up to 12 million people fell ill with smallpox, of which up to 1.5 million died. Its devastating power was not inferior to the power of the plague. The problem of protection against smallpox was solved only at the end of the 18th century by the English village doctor Edward Jenner. Jenner was the first to prove that by vaccination it is possible to suppress the spread of infectious diseases and expel them from the face of the Earth. The first mention of smallpox in Russia refers to the ΧV century. In 1610, the infection was brought to Siberia, where a third of the local population died. People fled to the forests of the tundra and the mountains set up idols, burned scars on their faces like backs to deceive this evil spirit - everything was in vain, nothing could stop the ruthless killer. Smallpox natural is an acute infectious disease characterized by general intoxication, fever and a rash on the skin and mucous membranes. Smallpox refers to quarantine infections. The source of infection is a sick person, starting from the first days of illness until the crusts completely fall off. The transmission of the pathogen occurs mainly by airborne droplets, however, infection is also possible by airborne dust. Smallpox was widespread in Asia, Africa, South America. In the USSR, smallpox was eradicated in 1937. It has now been eradicated throughout the world.
FLU
Influenza, according to our concepts, is not such a serious disease, but it remains the "king" of epidemics. None of the diseases known today can cover hundreds of millions of people in a short time, and more than 2.5 billion people fell ill with influenza in just one pandemic (general epidemic).
From the end of the nineteenth century mankind has experienced four severe influenza pandemics: in 1889-1890, 1918-1920, 1957-1959 and 1968-1969. Pandemic 1918-1920 ("Spaniard") carried away 20 million lives . Never before has influenza caused such a high mortality rate. In 1957-1959 ("Asian flu"), about 1 million people died.
There are several varieties of influenza virus - A, B, C, etc.; The internal part of the influenza virus - the nucleotide (or core) contains a single-stranded RNA enclosed in a protein case. This is the most stable part of the virion, as it is the same for all influenza viruses of the same type. Type A influenza is the culprit of pandemics. Influenza B is less common and causes more limited epidemics, influenza C is even rarer.
Due to the fact that the immunity to influenza is short-term and specific, it is possible to have a repeated illness in one season. According to statistics, an average of 20-35% of the population gets the flu every year.
The source of infection is a sick person; patients with a mild form, as spreaders of the virus, are the most dangerous, since they do not isolate themselves in a timely manner - they go to work, use public transport, and visit spectacular places. The infection is transmitted from a sick person to a healthy person by airborne droplets when talking, sneezing, coughing or through household items.
Avian influenza in humans:
Influenza A viruses can infect not only humans, but also some poultry species, including chickens, ducks, pigs, horses, ferrets, seals, and whales. Influenza viruses that infect birds are called "avian (chicken) flu" viruses. All types of birds can get avian influenza, although some species are less susceptible than others. Bird flu does not cause epidemics among wild birds; it is asymptomatic, but among domestic birds it can cause severe illness and death.
Avian influenza viruses generally do not infect humans, but human cases of illness and even death have been reported during the 1997-/>1999 and 2003-2004 outbreaks. In this case, a person is most likely the final link in the transmission of the influenza virus (you can get sick by contact with a live infected bird or by eating raw infected meat), because. So far, no cases of reliable transmission of this virus from person to person have been recorded.
So in 1997 in Hong Kong, an avian influenza virus (H5N1) was isolated, which infected both chickens and humans. This was the first time that an avian influenza virus could be directly transmitted from birds to humans. During this outbreak, 18 people were hospitalized and 6 of them died. Scientists determined that the virus spread directly from birds to humans.
Since the end of 2003, the avian influenza epidemic has swept through Southeast and East Asia and has killed 66 people, most of them in close contact with infected animals.
Also in 2003, avian influenza viruses (H7N7) and (H5N1) were detected in the Netherlands in 86 people caring for infected birds. The disease was asymptomatic or mild. The most common manifestations of the disease were limited to infection of the eyes with some signs of respiratory disease.
Recently, bird flu has been detected in Russia and Kazakhstan. However, no cases of injury dangerous virus people in these countries have not yet been recorded
Symptoms of bird flu in humans:
Symptoms of avian flu in humans range from typical flu-like symptoms (very high fever, difficulty breathing, cough, sore throat and muscle pain) to an eye infection (conjunctivitis). Such a virus is dangerous in that it can very quickly lead to pneumonia, and, in addition, it can cause severe complications in the heart and kidneys.
2004 - the most widespread outbreak of avian influenza (H5N1) among humans. The main distinguishing features of the 2004 influenza virus can be summarized as follows:
The virus has become more contagious, indicating that the virus has mutated.
The virus has crossed the species barrier from birds to humans, but so far there is no evidence that the virus is transmitted directly from person to person (all sick people had direct contact with an infected bird).
The virus infects and kills mostly children. The source of infection and the ways of spreading the virus have not been determined, which makes the situation with the spread of the virus practically uncontrollable. Measures to prevent the spread - the complete destruction of the entire poultry population. Treatment of avian influenza in humans:
Research so far confirms that prescribing drugs designed for human influenza strains will also be effective in human avian influenza infections, but it is possible that influenza strains may become resistant to such drugs and these drugs become ineffective. The isolated virus was found to be sensitive to amantadine and rimantadine, which inhibit the reproduction of the influenza A virus and are used in the treatment of human influenza.
What is the reason for the close attention to bird flu these days:
All influenza viruses have the ability to change. There is a possibility that in the future the avian influenza virus may change in such a way that it can infect humans and spread easily from person to person. Because these viruses do not normally infect humans, there is very little or no immune defense against such viruses in the human population.
If the avian influenza virus becomes capable of infecting humans, an influenza pandemic could begin. Experts from the World Health Organization (WHO) believe that the bird flu pandemic could lead to the death of 150 million people on Earth.
This fact is confirmed by American and British scientists: the results of their research indicate that the Spanish flu (1918) was so deadly due to the fact that it evolved from bird flu and contained a unique protein to which humans had no immunity.
The current hypothesis is that the pandemic influenza virus originated by gene transfer from a waterfowl reservoir to humans via pigs.
In addition, the bird flu virus, unlike the human one, is very stable in the external environment - even in the carcasses of dead birds, it can live up to one year, which increases the risk.
AIDS- Acquired immune deficiency syndrome is a new infectious disease that experts recognize as the first truly global epidemic in the known history of mankind. Neither plague, smallpox, nor cholera are precedents, since AIDS is decidedly unlike any of these and other known human diseases. The plague claimed tens of thousands of lives in the regions where the epidemic broke out, but never covered the entire planet at once. In addition, some people, having been ill, survived, acquiring immunity and took on the work of caring for the sick and restoring the affected economy. AIDS is not a rare disease that only a few people may accidentally suffer from. Leading experts currently define AIDS as a “global health crisis”, as the first truly all-terrestrial and unprecedented epidemic of an infectious disease that is still not controlled by medicine after the first decade of the epidemic and every infected person dies from it.
AIDS by 1991 was registered in all countries of the world except Albania. In the most developed country in the world - the United States, already at that time one of every 100-200 people was infected, another resident of the United States was infected every 13 seconds, and by the end of 1991, AIDS in this country came in third in terms of mortality, overtaking cancer. Currently, the number of people infected with the virus is leading the countries of Caugu from the Sahara. A whole country in Africa - Zimbabwe can die out as a result of AIDS: every day up to 300 people die from this disease here! Among the adult population of large cities in Botswana, the incidence reaches 30%. Every tenth infant is already infected with the HIV virus. So far, AIDS is forced to recognize itself as a fatal disease in 100% of cases.
The first people with AIDS were identified in 1981, and in 1983. managed to prove that it is caused by a previously unknown human virus from the family of retroviruses. The composition of this virus includes only its inherent enzyme - reverse transcriptase (RNA - dependent DNA pomerase), which is part of only these viruses. Its discovery was a real revolution in biology, as it showed the possibility transfer of genetic information not only according to the classical scheme DNA - RNA - protein, but also by reverse transcription from RNA to DNA. Thus, a “pseudo program” (provirus) appears in the cell, which changes the genome much more strongly than is possible with “normal” evolutionary variability.
In the human body retrovirus HIV infects only certain cells - the so-called T4 lymphocytes binding to a specific membrane protein. Unfortunately, it is these cells that play the main role V immune system management. When invading, the virus introduces its RNA, on the template of which the provirus DNA is synthesized, in order to then integrate into the genome of the host cell. In this capacity, HIV can be present in the body for up to ten years, without showing itself in any way.
But if, under the influence of some other infections, lymphocytes are activated, the built-in area “wakes up” and begins to actively synthesize HIV particles. Then the viruses destroy the membrane and kill the lymphocytes, which leads to the destruction of the immune system, as a result of which the body loses its protective properties and is unable to resist pathogens of various infections and kill tumor cells. The insidiousness of HIV in its unusually high ability to mutate- which makes it impossible to create an effective vaccine and a universal medicine.
How infection occurs ? The source of infection is a person affected by the immunodeficiency virus. This may be a patient with various manifestations of the disease, or a person who is a carrier of the virus, but does not have signs of the disease (asymptomatic virus carrier).
Ways of transmission: sexual,
AIDS is transmitted only from person to person:
1. Sexual way(horizontal way)
2. parenteral, when a viral agent is introduced directly into the blood of a susceptible organism (transfusion of blood or its preparations), organ transplantation or intravenous administration of drugs (drugs) with common syringes or needles, ritual rites associated with bloodletting, cuts with an HIV-infected instrument.
3. from the mother to the newborn fetus (vertical path).
AIDS risk groups are homosexual men, "intravenous" drug addicts, prostitutes, persons with a large number of sexual partners, frequent donors, hemophilia patients, children born from HIV-infected persons.
Prevention measures . The main condition is your behavior!
Features of the evolution of viruses at the present stage.
The evolution of viruses in the era of scientific and technological progress, as a result of the powerful pressure of factors, proceeds much faster than before. As examples of such intensively developing processes in the modern world, one can point to environmental pollution with industrial waste, the widespread use of pesticides, antibiotics, vaccines and other biological preparations, a huge concentration of population in cities, the development of modern vehicles, the economic development of previously unused territories, the creation of industrial animal husbandry with the largest number of population density of animal farms. All this leads to the emergence of previously unknown pathogens, changes in the properties and circulation pathways of previously known viruses, as well as significant changes in the susceptibility and resistance of human populations.
Influence of pollution of the external environment.
The current stage of development of society is associated with intensive pollution of the external environment. With certain indicators of air pollution by certain chemicals and dust from industrial waste, there is a noticeable change in the resistance of the body as a whole, and especially the cells and tissues of the respiratory tract. There is evidence that under these conditions, some respiratory viral infections, such as influenza, are noticeably more severe.
Consequences of the mass use of pesticides.
This may lead to the emergence of clones and populations of viruses with new properties and, as a result, new unexplored epidemics.
Conclusion
The fight against viral infections is fraught with many difficulties, among which the resistance of viruses to antibiotics should be especially noted. Viruses actively mutate, and new strains regularly appear against which no “weapon” has yet been found. First of all, this applies to RNA-containing viruses, the genome of which is usually larger and, therefore, less stable. To date, the fight against many viral infections is developing in favor of man, mainly due to the universal vaccination of the population for preventive purposes. Such activities eventually led to the fact that by now, according to experts, the variola virus has disappeared in nature. As a result of general vaccination in our country, in 1961. epidemic poliomyelitis has been eradicated. However, nature still tests a person, from time to time, presenting surprises in the form of new viruses that cause terrible diseases. The most striking example is the human immunodeficiency virus, the fight against which a person is still losing. Its spread is already consistent with a pandemic.
Bibliography:
1. N. Green. W. Stout. D. Taylor. "Biology" in 3 volumes, volume 1. Translation from English. Edited by R. Soper. Publishing house "Mir". Moscow, 1996
2. E.P. Shuvalov "Infectious diseases", 1990.
3.G.L.Bilich "Biology full course", 2005
4.N.B Chebyshev Biology, 2005
5. Golubev D.B., Soloukhin V.Z. "Reflections and Debates on Viruses". Moscow, publishing house "Young Guard", 1989.
7. Zhdanov V.M., Gaidamovich S.Ya. "General and private virology". M .: "Medicine", 1982.
8. Golubev D.B., Soloukhin V.Z. "Reflections and Debates on Viruses". M .: "Young Guard", 1982.
3. Zhdanov V.M., Ershov F.I., Novokhatsky A.S. "Secrets of the Third Kingdom". Moscow, ", 1971.
5. Zuev V.A. "Thirdly". Moscow, Znanie publishing house, 1985.
11. Cherkes F.K., Bogoyavlenskaya L.B., Belskaya N.A. "Microbiology". Moscow, publishing house "Medicine", 1987.
12. Chumakov M.P., Lvov D.K. “Issues of virology”. Moscow, publishing house of the Academy of Medical Sciences of the USSR, 1964.
13. A selection of articles under the general title "December 1 - World AIDS Day". Monthly popular science magazine "Health" No. 12 (513) for 1997, pp. 38-41.
Viruses. Surely you have repeatedly heard this name, heard about the harm that they represent for a person, heard about such viral infections like flu, measles, smallpox, herpes, hepatitis, HIV... But what are viruses and why are they so dangerous?
All viruses are non-cellular organisms, that is, they do not have a cellular structure, and this is their main difference from other types of organisms.
The average size of viruses ranges from 20 to 300 nanometers, making them the smallest of anything that the word "live" applies to. The average virus is about 100 times smaller than other pathogenic creatures, bacteria. The virus can only be seen with a sufficiently powerful electron microscope.
Once in the host cells, viruses begin to multiply spontaneously, and the building material is the substance of the cell itself, which often leads to its death. This is what all viral infections are dangerous for.
Interestingly, there are also beneficial viruses for humans, these are the so-called bacteriophages that destroy harmful bacteria inside us.
How are viruses arranged?
The structure of viral particles is as simple as possible, in most cases they consist of only two components, less often three:
genetic material in the form of DNA or RNA molecules - this is actually the basis of the virus, which contains information for its reproduction;
capsid - a protein shell that separates and protects genetic material from the external environment;
supercapsid - an additional lipid shell, which in some cases is formed from the membranes of donor cells.
Internal structure of a virus particle
What are viruses?
In form, all viruses can be divided into 4 large groups:
- spiral
- icosahedral and round
- oblong
- complex or incorrect
Typical forms of viruses
Viruses also spread in various ways, of which there are a huge number: through the air, through direct contact, through animal carriers, through the blood, etc.
Representatives of a non-cellular form of life are viruses - the smallest particles that penetrate inside the cell. The branch of microbiology that studies viruses is called virology.
general description
Viruses are found in the atmosphere, soil, and water. There are viruses of plants, animals, fungi, bacteria. Viruses that infect bacteria are called bacteriophages. There are satellites that enter the cell only if there is an additional virus in it.
Rice. 1. Bacteriophage.
Most viruses cause infections, some types have no visible effect. One of the interesting facts is the presence of virus residues in human DNA.
Viruses have a variety of shapes (balls, spirals, rods) and the smallest sizes - 20-300 nm (1 million nm in 1 mm). The largest viruses are mimiviruses, which have a diameter of 500 nm. They mimic the structure and activity of bacteria, and some scientists consider mimiviruses to be a transitional form from viruses to bacteria.
Rice. 2. Mimiviruses.
Briefly about viruses and their differences from living and non-living matter is presented in the table.
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who read along with thisViruses are allocated to a separate kingdom and are classified into five taxa. Most viruses have not yet been studied and classified.
The modern classification includes:
- 9 squads;
- 127 families;
- 44 subfamilies;
- 782 genera;
- 4686 species.
Biologist David Baltimore in 1971 developed an alternative classification of viruses according to the features of genetic information. Baltimore delineated which viruses are based on the content of RNA or DNA.
Its classification can be grouped into three major groups:
- DNA viruses;
- RNA viruses;
- Viruses that convert RNA to DNA.
The main types of viruses in biology in Baltimore are presented in the table.
Name |
Baltimore class |
Peculiarities |
Examples |
DNA viruses |
double stranded DNA. Reproduction in the cell nucleus |
Viruses of smallpox, herpes, papillomas |
|
Single stranded DNA. Reproduction in the nucleus |
Parvoviruses |
||
DNA is both double-stranded and single-stranded |
Hepatitis B virus |
||
RNA viruses |
double stranded RNA. reproduction in the cytoplasm |
Reoviruses, rotaviruses |
|
Single-stranded informative RNA (plus-strand) |
picornaviruses, flaviviruses |
||
Single-stranded RNA that does not carry information (negative strand) |
Orthomyxoviruses, filoviruses |
||
RNA and DNA |
Single-stranded RNA (plus-strand) turns into DNA |
Retroviruses (HIV) |
Viruses are structures that change the DNA of a cell, as a result of which the cell produces new viruses. When there are too many viruses, they break the cell membrane, go outside and infect new cells. Sometimes they do not kill the cell, but bud off from it.
Rice. 3. A virus that invades a cell.
What have we learned?
From the report of grades 5-6, they learned about the structure, features, and classification of viruses. They cannot be attributed either to living nature or to inanimate matter. By structure, viruses are proteins that carry hereditary information that is integrated into a living cell. Biologist Baltimore identified seven classes of viruses, depending on the structural features of the genetic material.
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