Discovery of viruses by D.I. Ivanovsky in 1892 laid the foundation for the development of the science of virology. Its faster development was facilitated by the invention of the electron microscope and the development of a method for cultivating microorganisms in cell cultures.

Currently, virology is a rapidly developing science, which is due to a number of reasons:

The leading role of viruses in human infectious pathology (examples are influenza virus, HIV human immunodeficiency virus, cytomegalovirus and other herpes viruses) against the background of the almost complete absence of specific chemotherapy;

The use of viruses to solve many fundamental questions in biology and genetics.

The main properties of viruses (and plasmids), by which they differ from the rest of the living world.

1. Ultramicroscopic dimensions (measured in nanometers). Large viruses (smallpox virus) can reach sizes of 300 nm, small ones - from 20 to 40 nm. 1 mm=1000 µm, 1 µm=1000 nm.

3. Viruses are not capable of growth and binary fission.

4. Viruses reproduce by reproducing themselves in an infected host cell using their own genomic nucleic acid.

6. The habitat of viruses is living cells - bacteria (these are bacterial viruses or bacteriophages), plant, animal and human cells.

All viruses exist in two qualitatively different forms: extracellular- virion and intracellular virus. The taxonomy of these representatives of the microcosm is based on the characteristics of virions, the final phase of viral development.

Structure (morphology) of viruses.

1. Virus genome form nucleic acids, represented by single-stranded RNA molecules (in most RNA viruses) or double-stranded DNA molecules (in most DNA viruses).

2. Capsid- a protein shell in which the genomic nucleic acid is packaged. The capsid consists of identical protein subunits - capsomers. There are two ways to package capsomers into a capsid—helical (helical viruses) and cubic (spherical viruses).

With spiral symmetry protein subunits are arranged in a spiral, and between them, also in a spiral, the genomic nucleic acid (filamentous viruses) is laid out. With cubic type of symmetry virions can be in the form of polyhedra, most often twenty-hedra - Icosahedrons.

3. Simply designed viruses only have nucleocapsid, i.e. the complex of the genome with the capsid is called “naked”.

4. Other viruses have an additional membrane-like shell on top of the capsid, acquired by the virus at the time of exit from the host cell - supercapsid. Such viruses are called “dressed”.

In addition to viruses, there are even more simply organized forms of agents capable of being transmitted - plasmids, viroids and prions.

The main stages of interaction between the virus and the host cell.

1. Adsorption is a trigger mechanism associated with interaction specific receptors of the virus and the host (in the influenza virus - hemagglutinin, in the human immunodeficiency virus - glycoprotein gp 120).

2. Penetration - by fusion of the supercapsid with the cell membrane or by endocytosis (pinocytosis).

3. Release of nucleic acids - “undressing” of the nucleocapsid and activation of the nucleic acid.

4. Synthesis of nucleic acids and viral proteins, i.e. subordination of the host cell systems and their work for the reproduction of the virus.

5. Assembly of virions - association of replicated copies of viral nucleic acid with capsid protein.

6. Exit of viral particles from the cell, acquisition of supercapsid by enveloped viruses.

Outcomes of the interaction of viruses with the host cell.

1. Abortion process- when cells are freed from the virus:

When infected defective a virus whose replication requires a helper virus, independent replication of these viruses is impossible (so-called virusoids). For example, hepatitis delta (D) virus can replicate only in the presence of hepatitis B virus, its Hbs - antigen, adeno-associated virus - in the presence of adenovirus);

When a virus infects cells that are genetically insensitive to it;

When sensitive cells are infected with a virus under non-permissive conditions.

2. Productive process- replication (production) of viruses:

- death (lysis) of cells(cytopathic effect) - the result of intensive reproduction and the formation of a large number of viral particles - a characteristic result of a productive process caused by viruses with high cytopathogenicity. The cytopathic effect on cell cultures for many viruses is of a fairly recognizable specific nature;

- stable interaction, which does not lead to cell death (persistent and latent infections) - the so-called viral transformation of a cell.

3. Integrative process- integration of the viral genome with the genome of the host cell. This is a special version of a productive process similar to stable interaction. The virus replicates along with the genome of the host cell and can remain latent for a long time. Only DNA viruses can integrate into the host DNA genome (the “DNA-in-DNA” principle). The only RNA viruses capable of integrating into the genome of a host cell, retroviruses, have a special mechanism for this. The peculiarity of their reproduction is the synthesis of proviral DNA based on genomic RNA using the reverse transcriptase enzyme, followed by the integration of DNA into the host genome.

Basic methods of cultivating viruses.

1. In the body of laboratory animals.

2. In chicken embryos.

3. In cell cultures - the main method.

Types of cell cultures.

1. Primary (trypsinized) cultures- chicken embryo fibroblasts (CHF), human fibroblasts (CHF), kidney cells of various animals, etc. Primary cultures are obtained from cells of various tissues most often by crushing and trypsinization and are used once, i.e. It is always necessary to have appropriate organs or tissues.

2. Diploid cell lines suitable for repeated dispersion and growth, usually no more than 20 passages (lose their original properties).

3. Interconnected lines(heteroploid crops), are capable of repeated dispersion and grafting, i.e. to multiple passages, most convenient in virological work - for example, tumor cell lines Hela, Hep, etc.

Special nutrient media for cell cultures.

A variety of synthetic virological nutrient media of complex composition are used, including a large set of different growth factors - medium 199, Needle, Hanks solution, lactalbumin hydrolyzate. pH stabilizers (Hepes), blood serum of various species (fetal calf serum is considered the most effective), L-cysteine ​​and L-glutamine are added to the media.

Depending on the functional use of the environment, there may be height(with a high content of blood serum) - they are used for growing cell cultures before adding viral samples, and supportive(with less serum content or no serum) - for maintaining virus-infected cell cultures.

Detectable manifestations of viral infection of cell cultures.

1. Cytopathic effect.

2. Identification of inclusion bodies.

3. Detection of viruses by fluorescent antibodies (MFA), electron microscopy, autoradiography.

4. Color test. The usual color of culture media used, containing phenol red as a pH indicator, under optimal cell culture conditions (pH about 7.2) is red. Cell reproduction changes the pH and, accordingly, the color of the medium from red to yellow due to a shift in pH to the acidic side. When viruses multiply in cell cultures, cell lysis occurs, and the pH and color of the medium do not change.

5. Detection of viral hemagglutinin - hemadsorption, hemagglutination.

6. Plaque method (plaque formation). As a result of the cytolytic effect of many viruses on cell cultures, zones of mass cell death are formed. Plaques are detected - viral “cell-negative” colonies.

Nomenclature of viruses.

The name of the family of viruses ends in “viridae”, genus - “virus”, special names are usually used for the species, for example, rubella virus, human immunodeficiency virus - HIV, human parainfluenza virus type 1, etc.

Bacterial viruses (bacteriophages).

The natural habitat of phages is a bacterial cell, so phages are distributed everywhere (for example, in wastewater). Phages have biological characteristics that are also characteristic of other viruses.

The most morphologically common type of phages is characterized by the presence of an icosahedral head, a process (tail) with spiral symmetry (often has a hollow rod and a contractile sheath), spines and processes (filaments), i.e. outwardly they somewhat resemble a spermatozoon.

The interaction of phages with a cell (bacterium) is strictly specific, i.e. bacteriophages are able to infect only certain species and phagotypes bacteria.

The main stages of interaction between phages and bacteria.

1. Adsorption (interaction of specific receptors).

2. The introduction of viral DNA (phage injection) is carried out by lysing a section of the cell wall with substances such as lysozyme, contracting the sheath, pushing the tail rod through the cytoplasmic membrane into the cell, and injecting DNA into the cytoplasm.

3. Phage reproduction.

4. Exit of daughter populations.

Basic properties of phages.

Distinguish virulent phages, capable of causing a productive form of the process, and temperate phages, causing reductive phage infection (phage reduction). In the latter case, the phage genome in the cell is not replicated, but is introduced (integrated) into the host cell chromosome (DNA in DNA), the phage turns into prophage This process is called lysogeny. If, as a result of the introduction of a phage into the chromosome of a bacterial cell, it acquires new heritable characteristics, this form of bacterial variability is called lysogenic (phage) conversion. A bacterial cell carrying a prophage in its genome is called lysogenic, since the prophage, if the synthesis of a special repressor protein is disrupted, can go into the lytic development cycle and cause a productive infection with lysis of the bacterium.

Temperate phages are important in the exchange of genetic material between bacteria - in transduction(one of the forms of genetic exchange). For example, only the causative agent of diphtheria has the ability to produce exotoxin, into whose chromosome is integrated a moderate prophage carrying operon tox, responsible for the synthesis of diphtheria exotoxin. The temperate phage tox causes lysogenic conversion of nontoxigenic diphtheria bacillus into toxigenic one.

According to the spectrum of action In bacteria, phages are divided into:

Polyvalent (lyse closely related bacteria, such as salmonella);

Monovalent (lyse bacteria of one type);

Type-specific (lyse only certain phage products of the pathogen).

On solid media, phages are more often detected using a spot test (formation of a negative spot during colony growth) or the agar layer method (Gracia titration).

Practical use of bacteriophages.

1. For identification (determination of phagotype).

2. For phage prophylaxis (stopping outbreaks).

3. For phage therapy (treatment of dysbacteriosis).

4. To assess the sanitary state of the environment and epidemiological analysis.



Viral diseases affect cells that already have abnormalities, which the pathogen takes advantage of. Modern research has proven that this only happens when the immune system is severely weakened and is no longer able to adequately fight the threat.

Features of viral infections

Types of viral diseases

These pathogens are usually distinguished by genetic characteristics:

• DNA – human cold viral diseases, hepatitis B, herpes, papillomatosis, chicken pox, lichen;
• RNA – influenza, hepatitis C, HIV, polio, AIDS.

Viral diseases can also be classified according to the mechanism of their effect on the cell:

• cytopathic - accumulated particles rupture and kill it;
• immune-mediated - the virus integrated into the genome sleeps, and its antigens come to the surface, putting the cell under attack by the immune system, which considers it an aggressor;
• peaceful – the antigen is not produced, the latent state persists for a long time, replication starts when favorable conditions are created;
• degeneration - the cell mutates into a tumor cell.

How is the virus transmitted?

The viral infection spreads:

1. Airborne. Respiratory viral infections are transmitted by drawing in particles of mucus splashed during sneezing.
2. Parenterally. In this case, the disease spreads from mother to child, during medical procedures or sex.
3. Through food. Viral diseases come from water or food. Sometimes they lie dormant for a long time, appearing only under external influence.

Why do viral diseases become epidemics?

Many viruses spread quickly and en masse, which provokes epidemics. The reasons for this are the following:

1. Ease of distribution. Many serious viruses and viral diseases are easily transmitted through droplets of saliva inhaled. In this form, the pathogen can maintain activity for a long time, and therefore is able to find several new carriers.
2. Reproduction rate. After entering the body, the cells are affected one by one, providing the necessary nutrient medium.
3. Difficulty in eliminating. It is not always known how to treat a viral infection, this is due to lack of knowledge, the possibility of mutations and difficulties in diagnosis - at the initial stage it is easy to confuse it with other problems.

Symptoms of a viral infection

The course of viral diseases may differ depending on their type, but there are common points.

1. Fever. Accompanied by a rise in temperature to 38 degrees, only mild forms of ARVI pass without it. If the temperature is higher, this indicates a severe course. It lasts no longer than 2 weeks.
2. Rash. Viral skin diseases are accompanied by these manifestations. They may appear as macules, roseolas, and vesicles. Characteristic of childhood, rashes are less common in adults.
3. Meningitis. Occurs due to enterovirus and is more common in children.
4. Intoxication– loss of appetite, nausea, headache, weakness and lethargy. These signs of a viral disease are caused by toxins released by the pathogen during its activity. The strength of the effect depends on the severity of the disease; it is more difficult for children; adults may not even notice it.
5. Diarrhea. Characteristic of rotaviruses, the stool is watery and does not contain blood.

Human viral diseases - list

It is impossible to name the exact number of viruses - they are constantly changing, adding to the extensive list. Viral diseases, the list of which is presented below, are the most famous.

1. Flu and colds. Their signs are: weakness, fever, sore throat. Antiviral drugs are used, and if bacteria are present, antibiotics are additionally prescribed.
2. Rubella. The eyes, respiratory tract, cervical lymph nodes and skin are affected. It spreads by airborne droplets and is accompanied by high fever and skin rashes.
3. Piggy. The respiratory tract is affected, and in rare cases, the testes are affected in men.
4. Yellow fever. Harmful to the liver and blood vessels.
5. Measles. Dangerous for children, affects the intestines, respiratory tract and skin.
6. . Often occurs against the background of other problems.
7. Polio. Penetrates into the blood through the intestines and breathing; when the brain is damaged, paralysis occurs.
8. Angina. There are several types, characterized by headache, high fever, severe sore throat and chills.
9. Hepatitis. Any variety causes yellowing of the skin, darkening of urine and colorlessness of feces, which indicates a violation of several body functions.
10. Typhus. Rare in the modern world, it affects the circulatory system and can lead to thrombosis.
11. Syphilis. After damage to the genital organs, the pathogen enters the joints and eyes and spreads further. It has no symptoms for a long time, so periodic examinations are important.
12. Encephalitis. The brain is affected, a cure cannot be guaranteed, and the risk of death is high.

The most dangerous viruses in the world for humans

The list of viruses that pose the greatest danger to our body:

1. Hantavirus. The pathogen is transmitted from rodents and causes various fevers, the mortality rate of which ranges from 12 to 36%.
2. Flu. This includes the most dangerous viruses known from the news; different strains can cause a pandemic; severe cases affect the elderly and young children more.
3. Marburg. Discovered in the second half of the 20th century, it is the cause of hemorrhagic fever. Transmitted from animals and infected people.
4. . It causes diarrhea, the treatment is simple, but in underdeveloped countries 450 thousand children die from it every year.
5. Ebola. As of 2015, the mortality rate is 42%, transmitted through contact with the fluids of an infected person. Signs are: a sharp increase in temperature, weakness, muscle and throat pain, rash, diarrhea, vomiting, and possible bleeding.
6. . Mortality is estimated at 50%, characterized by intoxication, rash, fever, and damage to the lymph nodes. Distributed in Asia, Oceania and Africa.
7. Smallpox. Known for a long time, it is dangerous only to people. Characterized by a rash, high fever, vomiting and headache. The last case of infection occurred in 1977.
8. Rabies. Transmitted from warm-blooded animals, it affects the nervous system. Once symptoms appear, treatment success is almost impossible.
9. Lassa. The pathogen is carried by rats and was first discovered in 1969 in Nigeria. The kidneys and nervous system are affected, myocarditis and hemorrhagic syndrome begin. Treatment is difficult, fever claims up to 5 thousand lives annually.
10. HIV. Transmitted through contact with the fluids of an infected person. Without treatment, there is a chance to live 9-11 years; its complexity lies in the constant mutation of strains that kill cells.

Fighting viral diseases

The difficulty of the fight lies in the constant change in known pathogens, making the usual treatment of viral diseases ineffective. This makes it necessary to search for new drugs, but at the present stage of medical development, most measures are developed quickly, before crossing the epidemic threshold. The following approaches have been adopted:

• etiotropic – preventing the reproduction of the pathogen;
• surgical;
• immunomodulatory.

Antibiotics for viral infections

During the course of the disease, the immune system is always suppressed; sometimes it needs to be strengthened to destroy the pathogen. In some cases, for a viral disease, antibiotics are additionally prescribed. This is necessary when a bacterial infection occurs, which can only be killed in this way. In case of a pure viral disease, taking these medications will not bring any benefit and will only worsen the condition.

Prevention of viral diseases

1. Vaccination– effective against a specific pathogen.
2. Strengthening immunity– prevention of viral infections in this way involves hardening, proper nutrition, and support with plant extracts.
3. Precautionary measures– exclusion of contacts with sick people, exclusion of unprotected casual sex.

Viruses are incredibly small, cell-free creatures. It is possible to observe them only through the most modern equipment. Viruses are something between dead and breathing matter. Outside the cell, viruses have a crystalline form and do not exhibit normal properties. Plant viruses, bacteria, animals, as well as satellite viruses.

The word “virus” is translated from Latin as “poison”. These non-cellular organisms were discovered during the analysis of tobacco leaf disease in the 19th century by D.I. Ivanovsky. And in 1898, Martin Beijerinck identified 5,000 different viruses. Currently there are several million. Virology is the name of the scientific discipline that deals with the study and research of viruses. Viruses are easy to find anywhere on Earth.

Viruses are divided into two types: bacteriophages and viroids. Viroids are short RNA particles without a protein border, consisting of a single chain. They cause various diseases in plants and animals. One of these diseases is dementia. As for bacteriophages, they break into the bacterial cell and destroy it. The structure of a bacteriophage is as follows: a protein shell and DNA acid, sometimes RNA. This is the most common group of viruses.

Basically, the structure of viruses is quite primitive. Parts of viruses are composed of special capsids - a protein shell or nucleic acids RNA, DNA. Viruses with a more complex structure have an appendage lipoprotein wall formed from the cytoplasmic layer of the host cell.

Viruses reproduce strictly in the cells of other creatures, transferring the gene to their cells. data and the cell, reading this data, produces similar viruses, as if duplicating them.

The most well-known viral diseases for humans are smallpox, hepatitis, chickenpox, and herpes. AIDS can be considered the most dangerous virus, for which a cure has not yet been developed.

Healing some ailments, for example, influenza and hepatitis, causes some difficulties due to the ability of most viruses to rapidly multiply and mutate in the cellular environment, so they are resistant to the strongest and most expensive drugs.

Option 2

All living creatures on earth are capable of being attacked by viruses. The virus is not visible to the human eye, but its reproduction inside the body is clearly noticeable. Viruses can only reproduce on the surface of a living cell, so only living beings suffer from viruses.

The discovery of the non-bacterial world occurred at the end of the 19th century. This is reflected in the work of Dmitry Ivansky, where he describes the tobacco virus. There are currently more than 100 million types of viruses, but only 100 thousand have been described. They are found in every part of the world. On any platform and enclosed space. A special science, virology, deals with the in-depth study of viruses.

The body of animals and partly humans is designed in such a way that during the active influence and reproduction of viruses in the body, it begins to produce an immune attack that tries to destroy the life of all viruses. Man invented a vaccine with which the immune attack is enhanced. In this case, the vaccine is adapted to a specific virus and destroys it. But there are more complex viruses that are able to move throughout the body and not be affected by the vaccine. Thus, a chronic pathology of disease in the body is formed. Scientists and pharmacists tried to create a drug that could act on viruses, but this was not possible.

From Latin, “virus” means poison. Since 1728, it has denoted a creature that can live inside an organism and cause diseases that can be transmitted to other organisms. Then people began to study them and discover the reasons for their occurrence, for example, the appearance of fungi, bacteria, and so on. For a long time they could not find the virus that leads to rabies, and at the same time the development of medicines and means to get rid of it began. After all the research at the end of the 19th century, viruses were no longer called bacteria and a separate group of viruses with their own distinctive characteristics was identified.

Viruses are quite dangerous creatures that not every microscope can see, which makes them difficult to study and combat. Their special ability to cause disease in the body does not have a beneficial effect on surrounding creatures. At the moment, they are also insufficiently studied and, accordingly, there is not enough knowledge to destroy them and remove them from living cells.

• Writer Marcel Proust. Life and art

  Marcel Proust was a famous novelist and representative of French modernism in the 20th century. M. Proust was born on July 10, 1871 in a rural suburb of the French capital into a fairly wealthy family. Vikings - message report (grades 5, 6. History. Geography)

  Vikings were inhabitants of Scandinavia from about 700 to 1125. This period is called the Viking Age. Vikings traveled long distances in their ships as traders, settlers and warriors

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 principles of cellular theory?

What viral diseases do you know?

In 1892, Russian botanist Dmitry Iosifovich Ivanovsky, studying mosaic disease of tobacco plants, discovered that when the juice isolated from a diseased plant was passed through filters that retained bacteria, the liquid retained the ability to cause diseases in healthy plants. The causative agent of the disease was so small that it and similar structures, which later received the name 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 consists of a nucleic acid (or DNA or RNA) and a protein. Nucleic acid is genetic material virus. It is surrounded by a protective protein shell - 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 virus capsid, consisting of many protein molecules, has a high degree of symmetry, usually having a spiral or polyhedral shape. This structural feature allows individual viral proteins to combine into a complete viral particle through self-assembly.

Rice. 46. ​​Viruses: structure and diversity

Rice. 47. Life cycle of viruses (A) and electron photograph of a bacteriophage (B)

Rice. 48. Bacteriophages on the surface of the host cell (electronic photography)

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. The tobacco mosaic virus, for example, infects tobacco plants, causing the formation of characteristic spots on the leaves - these are places where tissues die. The smallpox virus infects only epithelial cells, and the polio virus infects nervous tissue cells. Human viral diseases also include 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 people. The disease is currently spreading very quickly in Asia, Africa, and Central and Eastern Europe.

HIV belongs to the group retroviruses, the genetic material of which is RNA (Fig. 49). Typically, the transfer of genetic information in a cell occurs in the direction from DNA to RNA (transcription). In retroviruses, when they enter a 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 DNA.

Rice. 49. Human immunodeficiency virus (HIV): A – model of the virus; B – structure diagram; B – electronic photograph

Rice. 50. Life cycle of the human immunodeficiency virus (HIV)

Let's consider the life cycle of the immunodeficiency virus (Fig. 50). HIV infects and destroys white blood cells, including so-called helper lymphocytes. help- help), which ensure the formation of human immunity. After HIV enters the cell through endocytosis (Fig. 50, 1–3 ) viral RNA enters the cytoplasm (Fig. 50, 4 ), where on its basis, viral DNA is synthesized using a special enzyme (Fig. 50, 5 ). The latter penetrates through the pores into the cell nucleus and is integrated into the host DNA (Fig. 50, 6 ). Subsequently, when the cell divides, simultaneously with the copying of cellular DNA, the built-in viral DNA is also copied, as a result of which the number of infected lymphocytes grows rapidly. This process can continue for many years. After some time, the virus becomes active 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 leaving 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 cease to recognize foreign proteins and pathogenic bacteria entering the body, and the person becomes vulnerable to any infectious diseases. Every year, 1–2% of HIV-infected people develop AIDS. AIDS patients are susceptible to various bacterial, viral and fungal infections, which cause their death. More than 60% of people with AIDS die from pneumonia, which is usually successfully treated 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 subsequently lead to paralysis and coma.

HIV is usually transmitted through blood or semen. In 90% of cases, infection occurs through sexual contact, and 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 blood of a patient, for example when treating wounds. There is a risk of infection from blood transfusions that have not been tested for HIV. From an HIV-infected mother, the virus can enter the blood of the fetus through the placenta or be transmitted to the newborn through breastfeeding. But this virus does not spread through airborne droplets or a handshake.

HIV is a virus, so antibiotics that are used to treat bacterial infections are powerless in this case. Modern medicine is developing drugs that suppress HIV replication, but their use has many side effects and the prospects for their use are still unclear. Developing a vaccine against HIV also has its challenges; this is due to the structural features of this virus and the severity of the disease it causes. Today, 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 yourself from AIDS is to take the following precautions:

– you should avoid casual sexual intercourse, and during sexual intercourse, isolate yourself from the sperm and blood of your partner using a condom;

– in hospitals, dental clinics, clinics and beauty salons, it is necessary to use disposable syringes, and reusable instruments must be thoroughly sterilized, observing all the necessary conditions;

– Donated blood should be tested for the presence of HIV antibodies.

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 returned 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 cell receiving some foreign genetic information.

Many viruses are capable of not only introducing their hereditary information into the host’s body, but also, by integrating into the host’s DNA, changing the functioning of cellular genes. In the process of copying viral DNA, partial copying of the host's genetic material sometimes occurs. In this case, the newly assembled viral particles leaving the cell will take with them a copy of some hereditary information of the host. 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 causative agents of infectious diseases, but also as carriers of genes between organisms.

Review questions and assignments

1. How do viruses work?

2. What is the principle of interaction between a virus and a cell?

3. Describe the process of virus penetration into 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 and the classifications created by your classmates.

Think! Do it!

1. Explain why a virus can exhibit the properties of a living organism only by invading a living cell.

2. Why do viral diseases become epidemics? Describe measures to combat viral infections.

3. Express your opinion about the time of appearance of viruses on Earth in the historical past, taking into account that viruses can only reproduce in living cells.

4. Explain why in the middle of the 20th 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 the transfer of genes from parents to children called?

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.

Find out more

Viroids. Infectious agents found in nature are much smaller 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. They are believed to be excised sections of mRNA that have acquired the ability to replicate. However, they do not work like mRNA and do not code for proteins.

Once in plant cells, viroids interfere with the genome of the host cell and cause serious plant diseases. This is how millions of coconut trees died in the Philippines in the second half of the 20th century. From time to time, plantings of potatoes, citrus fruits, cucumbers, ornamental flowers and other wild and agricultural plants are seriously affected by viroids. Viroids have not yet been found in animal cells or humans.

Viruses and cancer. Many viruses are capable of penetrating into the cells of the body and integrating their genome into the genome of the cell, thereby causing serious disruptions in the functioning of the genetic apparatus of normal cells. As a result, a normal cell can transform into a cancerous one.

Dozens of viruses that cause cancer have been found in many animals (fish, amphibians, birds, mammals). Entire groups of oncoviruses have been discovered in humans. It is believed that about 15% of human tumors are caused by a viral infection.

Repeat and remember!

Human

Immunity. Proteins or polysaccharides of viruses that enter the body are antigens. Antigens– these are any foreign substances that, upon penetration into the body, are perceived as genetically foreign and cause an immune reaction. Immunity is the ability of organisms to protect themselves from 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 occurs in a person without any special influence, it is called natural. Immunity obtained through the use of medications is called artificial.

Natural innate immunity is the same in all individuals of the species and is inherited, i.e., genetically fixed. Thus, humans do not suffer from many diseases that occur in animals. For example, a person will never get canine distemper, just as a dog will never get the flu.

Natural acquired immunity differs from person to person and is not inherited, which is why 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. This type of immunity is also called post-infectious immunity. It remains in the body for a long time. After some diseases, immunity lasts for life, for example after measles, rubella, scarlet fever and other “childhood diseases”.

Artificial immunity can only be acquired. Artificial active immunity is formed in response to the introduction of a vaccine into the body. Vaccine is a preparation made from weakened or killed pathogens, their fragments or toxins. When a vaccine is administered (vaccination), a weak immune response develops in the body, as a result of which special cells are formed in the blood that are capable of synthesizing antibodies to this pathogen. Antibodies- These are complex proteins (immunoglobulins). They are able to bind to antigens and neutralize them. When antigen binds, an inactive antigen-antibody complex is formed, which can be destroyed by leukocytes.

Artificial active immunity is persistent and lasts for years. For the first time, systematic vaccinations against smallpox began to be used at the beginning of the 19th century. after the works of the English physician Edward Jenner (1749–1823). His work was continued by the French microbiologist Louis Pasteur (1822–1895). He coined the term “vaccine” and used vaccination in medical practice.

Artificial passive immunity occurs when a person is given a medicinal serum, which already contains ready-made antibodies against the pathogen. This is especially important if infection has already occurred. Passive immunity is unstable and lasts for 4–6 weeks, during which the 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 fields of natural sciences.

2. What professions in modern society require knowledge of the structure and vital functions of prokaryotic organisms? Prepare a short (no more than 7-10 sentences) message about the profession that most impressed you. Explain your choice.

3. “These specialists are needed in veterinary and medical research institutes, academic institutes, and biotechnology-related enterprises. They will not be left without work in 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 cancer.” Guess which professions we are talking about in these sentences. Prove your point.

This text is an introductory fragment. From the book The Story of a Fish author Pravdin Ivan Fedorovich

Body shape of fish The body shape of fish is so diverse that it is impossible to give it a general description. When we pronounce the words “bird” and “beast,” we immediately imagine in the first case an animal with wings, in the second – with four legs. And about fish you can only

From the book Theoretical Foundations of Training author Gritsenko Vladimir Vasilievich

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From the book Comparative analysis of various forms of social learning in animals author Reznikova Zhanna Ilyinichna

Active instruction as a form of social learning Active instruction (“teaching”) is the most complex form of signaling heredity. All situations of teaching in animals described in the scientific literature concern the transfer of skills from elders.

From the book Dentistry of Dogs author Frolov V V

Dog head shape and areas Different dog breeds have a certain shape of the skull. This happened in the process of breeding a large number of breeds of one or another service direction. When breeding new breeds of dogs, people took into account a number of service

From the book Naughty Child of the Biosphere [Conversations about human behavior in the company of birds, animals and children] author Dolnik Viktor Rafaelevich

Is there a form of marriage that is “natural” for humans? Thinkers of the 19th century believed that initially primitive man had promiscuity (indiscriminate mating of everyone with everyone). We now know that this is not true. Firstly, the child has a pronounced

From the book Microbiology: lecture notes author Tkachenko Ksenia Viktorovna

2. ECHO viruses. Coxsackie viruses Belong to the Picornaviridae family, a genus of enteroviruses. The structure of the virion is the same as that of the polio virus. ECHO viruses are classified as a special group of intestinal viruses due to the complete absence of a pathogenic effect on laboratory animals.

From the book Microbiology author Tkachenko Ksenia Viktorovna

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From the book The New Science of Life author Sheldrake Rupert

3.2. Form and energy In Newtonian physics, all causality was considered in the language of energies, from the standpoint of the principle of motion and change. All moving things have energy - the kinetic energy of moving bodies, thermal vibrations and electromagnetic radiation - and this

From the book Human Race by Barnett Anthony

Body shape The highest height is among the Sudanese and blacks living in the Lake Chad region, in Central Africa, the lowest (150 centimeters) is among the pygmies, also living in Central Africa. Tall blacks live next to the pygmies, eat the same food as them, but are taller than them

From the book Fundamentals of Psychophysiology author Alexandrov Yuri

2.1 Size and shape The sizes of neurons can range from 1 (the size of a photoreceptor) to 1000 μm (the size of a giant neuron in the marine mollusk Aplysia) (see [Sakharov, 1992]). The shape of neurons is also extremely diverse. The shape of the neurons is most clearly visible when preparing the drug.

From the book Problems of Ethology author Akimushkin Igor Ivanovich

Movement is the simplest form of behavior. Tropisms The first most clear difference between animals and plants is clear to everyone: plants cannot move, while animals have this property. And yet it is precisely the movement of plants (turning flowers towards the sun)

From the book Genes and the development of the body author Neyfakh Alexander Alexandrovich

A special form of cognition is games “According to W. Thorpe, the play of... animals is always associated with an element of cognition... W. Thorpe emphasizes that a game can have several purposes. It helps to develop the “motor functions of a young animal,” but the game can be “played for its own sake.”

From the book In the World of the Invisible author Blinkin Semyon Alexandrovich

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From the book Biophysics Knows Cancer author Akoev Inal Georgievich

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From the author's book

Chapter II. Viruses in nature and human life

From the author's book

Leukemia is a generalized form of cancer. Cancer is a problem of the 20th century. The strictly scientific definition of “cancer” unites only malignant tumor diseases of the skin and its derivatives. A broader concept of cancer, common, in particular, among non-specialists