Remember!
How are viruses different from all other living things?
Why does the existence of viruses not contradict the basic principles of cellular theory?
Consist of organic substances like cells (proteins, nucleic acids)
Reproduce using cells
What viral diseases do you know?
Flu, HIV, rabies, rubella, smallpox, herpes, hepatitis, measles, papilloma, polio.
Review questions and assignments
1. How do viruses work?
Viruses have a very simple structure. Every virus consists of a nucleic acid (or DNA or RNA) and a protein. Nucleic acid is the genetic material of the virus. It is surrounded by a protective protein shell - the capsid. The capsid may also contain its own viral enzymes. Some viruses, such as influenza and HIV, have an additional envelope that is formed from the cell membrane of the host cell. The virus capsid, consisting of many protein molecules, has high degree 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.
2. What is the principle of interaction between a virus and a cell?
3. Describe the process of virus penetration into a cell.
“Naked” viruses penetrate the cell through endocytosis - immersion of a section of the cell membrane at the site of their adsorption. Otherwise, this process is known as viropexis [virus + Greek. pexis, attachment]. “Dressed” viruses enter the cell by fusion of the supercapsid with the cell membrane with the participation of specific F-proteins (fusion proteins). Acidic pH values promote the fusion of the viral envelope and the cell membrane. When “naked” viruses penetrate the cell, vacuoles (endosomes) are formed. After the penetration of “dressed” viruses into the cytoplasm, partial deproteinization of virions and modification of their nucleoprotein (undressing) occurs. Modified particles lose their infectious properties; in some cases, sensitivity to RNase, the neutralizing effect of antibodies (AT) and other characteristics specific to certain groups of viruses change.
4. What is the effect of viruses on the cell?
Think! Remember!
1. Explain why a virus can exhibit the properties of a living organism only by invading a living cell.
A virus is a non-cellular form of life, it does not have any organelles that perform certain functions in cells, there is no metabolism, viruses do not feed, do not reproduce on their own, and do not synthesize any substances. They only have heredity in the form of a single nucleic acid - DNA or RNA, as well as a capsid of proteins. Therefore, only in the host cell, when the virus integrates its DNA (if it is a retro virus, then reverse transcription occurs first and is built from RNA-DNA) into the DNA of the cell, can new viruses be formed. During replication and further synthesis of nucleic acids and proteins by the cell, all the information of the virus entered by it is also reproduced, and new viral particles are assembled.
2. Why do viral diseases have the nature of epidemics? Describe measures to combat viral infections.
They spread quickly by airborne droplets.
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.
Viruses multiply quickly, are easy to become infected, cause epidemics and pandemics, and can serve as mutagens for humans, animals and plants.
5. What difficulties arise when trying to create a vaccine against HIV infection?
Since HIV destroys the human immune system, and the vaccine is made from weakened or killed microorganisms, their metabolic products, or from their antigens obtained by genetic engineering or chemical means. The immune system will not withstand this action.
6. Explain why the transfer of genetic material by viruses from one organism to another is called horizontal transfer. What then, in your opinion, is the transfer of genes from parents to children called?
Horizontal gene transfer (HGT) is a process in which an organism transfers genetic material to another organism that is not its descendant. Vertical gene transfer is the transfer of genetic information from a cell or organism to its offspring using conventional genetic mechanisms.
7. Over the years, at least seven Nobel Prizes in physiology or medicine and three Nobel Prizes in chemistry 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.
Humanity's fight against the AIDS epidemic continues. And although it is too early to draw conclusions, certain, undoubtedly optimistic trends can still be traced. Thus, biologists from America managed to grow immune cells in which the human immunodeficiency virus cannot reproduce. This was achieved using the latest technology, which allows one to influence the functioning of the cell’s hereditary apparatus. University of Colorado professor Ramesh Akkina and his colleagues have designed special molecules that block the work of one of the key genes of the immunodeficiency virus. Then scientists made an artificial gene capable of synthesizing such molecules, and with the help of a carrier virus, introduced it into the nuclei of stem cells, which subsequently give rise to immune cells already protected from HIV infection. However, only clinical trials will show how effective this technique will be in the fight against AIDS.
Just 20 years ago, the disease was considered incurable. In the 90s, only short-lived interferon-alpha preparations were used. The effectiveness of this treatment was very low. Over the past decade, the “gold standard” in the treatment of chronic hepatitis C has been combined antiviral therapy with pegylated interferon-alpha and ribavirin, the effectiveness of which in eliminating the virus, that is, curing hepatitis C, generally reaches 60-70%. Moreover, among patients infected with genotypes 2 and 3 of the virus, it is about 90%. At the same time, the cure rate in patients infected with virus genotype C, until recently, was only 40-50%.
1. Features of vital functions (dimensions)
2. Scheme of the structure of the virus
3. Scheme of cell penetration and reproduction
4. Poems and riddles about viruses
4.Riddles and poems
I look sad -
My head hurts in the morning
I'm sneezing, I'm hoarse.
What's happened?
This is... the flu
This flu is a sneaky virus
My head hurts now
The temperature has risen
And you need some medicine
Has your child got measles?
It's not grief at all
The doctor will help, hurry
Our baby will be healed
I'm going to get vaccinated
I will proudly go to the doctor
Give me a syringe and an injection
All is ready? I went
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.
Biophysicists and biochemists will not be able to do without such knowledge. Physical and chemical processes proceed according to the same laws.
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.
Systems biotechnologist. Specialist in replacing outdated solutions in various industries with new products from the biotechnology industry. For example, it will help transport companies switch to biofuel instead of diesel, and construction companies to switch to new biomaterials instead of cement and concrete. Use biotechnology to purify liquid media.
3. “These specialists are needed in veterinary and medical research institutes, academic institutes, 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.
Probably genetics. Working with genetic material, they can work in any field related to living organisms, be it selection or any branch of medical knowledge.
Viruses were discovered by D.I. Ivanovsky (1892, tobacco mosaic virus).
If viruses are isolated in their pure form, then they exist in the form of crystals (they do not have their own metabolism, reproduction and other properties of living things). Because of this, many scientists consider viruses to be an intermediate stage between living and nonliving objects.
Viruses are non-cellular life forms. Viral particles (virions) are not cells:
- viruses are much smaller than cells;
- viruses are much simpler in structure than cells - they consist only of nucleic acid and a protein shell, consisting of many identical protein molecules.
- viruses contain either DNA or RNA.
Synthesis of virus components:
- The nucleic acid of the virus contains information about viral proteins. The cell makes these proteins itself, on its ribosomes.
- The cell reproduces the nucleic acid of the virus itself, using its enzymes.
- Then the self-assembly of viral particles occurs.
Virus meaning:
- cause infectious diseases (flu, herpes, AIDS, etc.)
- Some viruses can insert their DNA into the chromosomes of the host cell, causing mutations.
AIDS
The AIDS virus is very unstable and is easily destroyed in air. You can become infected with it only through sexual intercourse without a condom and through a transfusion of contaminated blood.
Answer
Establish a correspondence between the characteristics of a biological object and the object to which this characteristic belongs: 1) bacteriophage, 2) E. coli. Write numbers 1 and 2 in the correct order.
A) consists of nucleic acid and capsid
B) cell wall made of murein
C) outside the body is in the form of crystals
D) can be in symbiosis with humans
D) has ribosomes
E) has a tail canal
Answer
Choose one, the most correct option. Science studies precellular life forms
1) virology
2) mycology
3) bacteriology
4) histology
Answer
Choose one, the most correct option. The AIDS virus infects human blood
1) red blood cells
2) platelets
3) lymphocytes
4) blood platelets
Answer
Answer
2. Choose three correct answers out of six and write down the numbers under which they are indicated. Viruses as opposed to bacteria
1) have an unformed core
2) reproduce only in other cells
3) do not have membrane organelles
4) carry out chemosynthesis
5) capable of crystallizing
6) formed by a protein shell and nucleic acid
Answer
3. Choose three correct answers out of six and write down the numbers under which they are indicated. Viruses as opposed to bacteria
1) have a cellular structure
2) have an unformed core
3) formed by a protein shell and nucleic acid
4) belong to free-living forms
5) reproduce only in other cells
6) are a non-cellular form of life
Answer
Answer
Choose one, the most correct option. The cells of which organisms are affected by the bacteriophage?
1) lichens
2) mushrooms
3) prokaryote
4) protozoa
Answer
Choose one, the most correct option. The immunodeficiency virus primarily affects
1) red blood cells
2) platelets
3) phagocytes
4) lymphocytes
Answer
Choose one, the most correct option. In what environment does the AIDS virus usually die?
1) in the lymph
2) in breast milk
3) in saliva
4) in the air
Answer
Choose one, the most correct option. Viruses have such signs of living things as
1) food
2) growth
3) metabolism
4) heredity
Answer
Answer
1. Establish the correct sequence of stages of reproduction of DNA viruses. Write down the corresponding sequence of numbers in the table.
1) release of the virus into the environment
2) virus protein synthesis in the cell
3) introduction of DNA into the cell
4) synthesis of viral DNA in the cell
5) attachment of the virus to the cell
Answer
2. Set the sequence of steps life cycle bacteriophage. Write down the corresponding sequence of numbers.
1) biosynthesis of DNA and bacteriophage proteins by a bacterial cell
2) rupture of the bacterial membrane, release of bacteriophages and infection of new bacterial cells
3) penetration of bacteriophage DNA into the cell and its integration into the circular DNA of the bacterium
4) attachment of the bacteriophage to the bacterial cell membrane
5) assembly of new bacteriophages
Answer
Answer
Answer
1. Establish a correspondence between the characteristic of an organism and the group for which it is characteristic: 1) prokaryotes, 2) viruses.
A) cellular structure of the body
B) the presence of its own metabolism
C) integration of one’s own DNA into the DNA of the host cell
D) consists of a nucleic acid and a protein shell
D) reproduction by division in two
E) the ability to reverse transcription
Answer
Answer
Answer
Answer
Answer
Answer
Choose two correct answers out of five and write down the numbers under which they are indicated. Metabolism as a property of living things is characteristic of
1) plant viruses
2) protozoa
3) soil bacteria
4) animal viruses
5) bacteriophages
Answer
© D.V. Pozdnyakov, 2009-2019
Virions are inert forms that do not reproduce themselves, but only exist for transmission from one organism to another and for passage from one host cell to another and preservation in the external environment. In the latter case, they seem to resemble the role of spore forms of microorganisms.
Reproduction of viruses is the result of replication of their genome and reproduction of other structural components of the virion. These processes occur inside the infected cell. In order for a virus to replicate, it must first infect a cell; To infect a cell, the virus must contact the cell surface, penetrate the cell and “undress” to such an extent that its genome becomes capable of realizing its genetic functions, resulting in the appearance of new progeny of the virus. The host spectrum of different viruses varies significantly, it is determined both by the animal species and the types of cells in which this virus can reproduce.
Alone viruses have a wide range of hosts, others infect only cells of one type of certain animal species. The ability of cells and the body to become infected with a virus is called sensitivity and susceptibility, respectively. When a susceptible organism comes into contact with the virus, initially only sensitive cells at the entry point of infection (for example, the tonsils) are infected. However, this may not be enough for the clinical manifestation of the infection, since the disease occurs due to infection of target cells (for example, neurons, hepatocytes) after the virus has multiplied at the site of entry into the body. In some cases, target cells are located at the entrance gates of infection (for example, intestinal, respiratory infections).
The events that occur in an infected cell can vary significantly and their final result can also be different - from virus replication(productive infection) with destruction or/without destruction of cells until the transformation of cells that acquire the ability for unlimited division.
Many cytopathogenic viruses have the ability to establish a persistent infection in sensitive cells. The molecular mechanisms of viral persistence in cell cultures have not been fully elucidated.
Virus replication occupies a central place in molecular biology. The basic principles of viral replication were initially studied in experiments with bacteriophages, and with the advent of mammalian cell cultures, these methods were adapted to animal viruses.
At the beginning of infections, the cell enters viral genome(RNA K or DNA), often together with the necessary virion proteins. Despite significant differences in the reproduction strategy of different families of DNA and RNA viruses, especially with regard to the transcription and replication of their genomes, this process has common characteristic features that are characteristic of all viruses. The main one is that the ability of viruses to reproduce and the fate of infected cells depend on the synthesis and function of viral gene products - proteins, which ensure: a) replication of the viral genome and synthesis of viral proteins, b) packaging of the genome into viral particles (virions) and c) changes in the structure and/or function of infected cells.
Strategy applied viruses to provide these functions varies. Sometimes viral proteins (papilloma and polyomaviruses) simply help host cell enzymes replicate the viral genome. In most cases, viral proteins themselves ensure the replication of the viral genome, but even the most independent viruses, as a rule, use at least several host proteins.
“Well, I caught the virus again!” So, peering closely at the scale of the hot thermometer, parents inform us about the existence of these mysterious little dirty tricks. In addition to annoyance, there are alarming notes in the voices of adults. Probably not every parent knows that the word “virus” is translated from Latin as “poison,” but everyone has definitely heard about the great epidemics of the past and the deadly threats lurking in modern megacities - about influenza, hepatitis, AIDS... So what? What kind of creatures or substances are these - viruses? And are they all that scary?
In general, viruses are wonderful. They look great and are perfectly adapted to use any living organisms for their purposes: animals, plants, fungi, protozoa, bacteria and archaea. And even non-cellular creatures, brother viruses.
How do viruses work?
In the simplest case, a virus consists of genome(single- or double-stranded nucleic acid molecule) and protein shell. If there is no shell, then the object does not reach the title of virus and is content with the name viroid. Nucleic acid - DNA or RNA- encodes proteins necessary for virus reproduction. In some viruses, the genome contains instructions for building just a couple of proteins, in others - two thousand or more. protein coat, or capsid, protects the nucleic acid from damage and consists of several repeating parts - capsomeres, which, in turn, are built from molecules of one or more types of protein. The capsid can have the shape of an icosahedron (twenty-hedron, but not always regular), a thread or a stick, or it can combine different shapes: for example, in most bacterial viruses - bacteriophages- the icosahedral “head” is mounted, like a popsicle, on a rod-shaped hollow process.
But not all viruses are designed so simply: some are covered on top with additional, stolen from the host and slightly modified lipid membrane, loaded with host and viral proteins - they are very useful for infecting new cells. This is done, for example, by influenza and human immunodeficiency viruses (HIV). Very complex viruses, for example, vaccinia virus or mimivirus, can boast multi-layered “clothing”. They are able to transport in their particles many useful molecules - enzymes and factors necessary for the construction of new virions. Most viruses are forced to rely only on the host protein synthesis system.
How do viruses reproduce?
If a living cell reproduces by division, the virus repeatedly copies its “spare parts” in the affected cell. Any cell of any organism is not suitable for it - it needs a special one, which the virus recognizes by special molecules on the cell surface, receptors. Therefore, humans are not afraid of many viruses of other mammals, and HIV can begin its subversive activities only after contact with specific cells of the immune system. When the long-awaited meeting occurs, the virus enters the cell through damage (as plant viruses like to do) or by merging its outer shell with the cell membrane, or can inject, like a syringe, its genome through the cell wall (most bacteriophages do this) or be swallowed by the cell itself, which has not noticed the trick.
In the cell, the virus completely or partially “undresses.” If the virus genome is represented by DNA, then the process of copying it, or replication, occurs in the cell nucleus. Most viruses begin to exploit foreign, host enzymes from this stage. To produce other components of the virion, it is necessary to rewrite the information contained in the DNA in a slightly different language. Begins transcription: DNA copies are used to synthesize strands of RNA - intermediaries that will transmit ( broadcast) instructions stored in DNA for the cellular protein-making machines. Only on the basis of such intermediaries can proteins be built. This already happens in the cytoplasm and, of course, on the host equipment - ribosomes. That is, the virus forces the cell to work only for it and sacrifice its needs. The cell suffers from a deficiency of its own and the production of foreign substances and can even commit suicide. But even without that, her fate is unenviable. New components of the viral capsid bind to new nucleic acid molecules - self-assembly of virions occurs, which can bud off from the cell like a guerrilla, wrapped in its membrane, or can jump out in a single dashing impulse, and the crippled cell will burst ( lyses).
The most prudent viruses hide “tightly” until they feel that the right moment has come for active reproduction. These are, for example, herpes viruses and some bacteriophages. Some of them never have time to awaken.
And viruses of viruses generally rarely harm their “hosts”. And it’s difficult to call viruses hosts. It’s just that their factories for the production of virions are being used by host viruses without asking. True, certain types - virophages- can promote the survival of cells suffering from these very “hosts”.
Are all viruses bad guys?
Not only humans, but also animals and plants suffer from viruses. However, such complex living organisms have encountered viruses since their inception and have therefore adapted to coexist with most of them. And, as a rule, the virus has no need to kill its hosts - then it will have to look for new ones all the time, and if in crowded bacterial communities this is not so difficult, then in human...
The defense systems of our body cope well with most viruses, so nothing special was even invented for the treatment of mild intestinal disorders and “colds” caused by various agents. While you are looking for the true culprit, the person is already recovering. Moreover, viruses can also be our allies: using viruses as an example, biologists study various molecular processes, and they are also used for genetic engineering; at the same time, bacteriophages are able to deal with pathogenic bacteria, and some “dormant” herpes viruses may be able to protect against infection... with the plague.
But if we ignore the good and evil, from a human point of view, of viruses, we must admit that our world largely rests on these invisible creatures: they transfer their own and other people’s genes from organism to organism, increasing genetic diversity, and regulate the number of communities of living beings and are simply necessary for the circulation of nutrients, because viruses are the most numerous biological objects on our planet.
creative work
Virus propagation method
A virus (from Latin virus - poison) is a microscopic particle that can infect the cells of living organisms.
Virology (from virus and logos - word, doctrine), the science of viruses. General virology studies the nature of viruses, their structure, reproduction, biochemistry, and genetics.
The method of reproduction of viruses also differs from the division, budding, sporulation or sexual process that occurs in unicellular organisms, in cells of multicellular organisms and in the latter in general. Reproduction, or replication, is the common term for the reproduction of viruses. The formation of virions occurs either by self-assembly (packaging of viral nucleic acid into protein capsids and formation of a nucleocapsid), or with the participation of the cell, or both (enveloped viruses). Of course, the opposition between mitotic cell division and replication is not absolute, since the methods of replication of genetic material in DNA-containing viruses are not fundamentally different, and if we take into account that the synthesis of genetic material in RNA-containing viruses is also carried out according to the template type, then the opposition is relative mitosis and replication of all viruses. And, nevertheless, the differences in the methods of reproduction of cells and viruses are so significant that the entire living world can be divided into viruses and non-viruses.
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Mutation of viruses, characteristics of mutagens
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