Remember!

How are viruses different from all other living things?

Why does the existence of viruses not contradict the basic tenets of cell theory?

Composed of organic substances like cells (proteins, nucleic acids)

Reproduce by means of cells

What do you know about viral diseases?

Influenza, HIV, rabies, rubella, smallpox, herpes, hepatitis, measles, papilloma, polio.

Review questions and assignments

1. How are viruses arranged?

Viruses have a very simple structure. Every virus is made up 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 coat called the capsid. The capsid may also contain its own viral enzymes. Some viruses, such as the influenza virus and HIV, have an extra envelope that 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.

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

3. Describe the process of virus penetration into the cell.

"Naked" viruses enter the cell by 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 enter the cell, vacuoles (endosomes) are formed. After the penetration of the "dressed" viruses into the cytoplasm, a partial deproteinization of the virions and modification of their nucleoprotein (undressing) occur. The modified particles lose their infectious properties; in some cases, the sensitivity to RNase, the neutralizing action of antibodies (AT), and other signs specific to individual groups of viruses change.

4. What is the effect of viruses on the cell?

Think! Remember!

1. Explain why a virus can show 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 multiply on their own, and do not synthesize any substances. They have only heredity in the form of a single nucleic acid-DNA or RNA, as well as a protein capsid. Therefore, only in the host cell, when the virus inserts its DNA (if it is a retrovirus, then reverse transcription occurs first and is built according to RNA-DNA) into the DNA of the cell, new viruses can form. During replication and further synthesis of nucleic acids and proteins by the cell, at the same time all the information of the virus entered by it is reproduced, and new viral particles are assembled.

2. Why do viral diseases have the character of epidemics? Describe measures to combat viral infections.

Spread quickly, by airborne droplets.

3. Express your opinion about the time of the appearance of viruses on Earth in the historical past, given that viruses can only multiply 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.

Viruses multiply rapidly, they 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 called the transfer of genes from parents to children?

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, no doubt, optimistic trends can still be traced. So, biologists from America managed to grow immune cells in which the human immunodeficiency virus cannot multiply. This was achieved with the help of the latest technique, which allows to influence the work of the hereditary apparatus of the cell. University of Colorado professor Ramesh Akkina and his colleagues have designed special molecules that block the work of one of the key genes of the immunodeficiency virus. Then the 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.

Even 20 years ago, the disease was considered incurable. In the 1990s, only preparations of short-lived interferon-alpha 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 the combined antiviral therapy with pegylated interferon-alpha and ribavirin, the effectiveness of which in relation to the elimination of the virus, that is, the cure of hepatitis C, reaches a total of 60-70%. At the same time, among patients infected with 2 and 3 virus genotypes, it is about 90%. At the same time, the cure rate in patients infected with the C virus genotype, until recently, was only 40-50%.

1. Features of life activity (dimensions)

2. Scheme of the structure of the virus

3. Scheme of penetration into the cell, reproduction

4. Poems and riddles about viruses

4. Riddles and poems

I look sad,

Head hurts in the morning

I sneeze, I'm hoarse.

What's happened?

It's ... the flu

Vile virus this flu

Head hurts now

The temperature has risen

And you need a potion

Did the baby get measles?

It's not grief at all.

The doctor will help, hurry up

Heal our baby

I'm going to get vaccinated

Proudly I will come to the doctor

Give a syringe and an injection

Everything 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 areas of the natural sciences.

Biophysicists, biochemists cannot 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 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.

Systems biotechnologist. Specialist in replacing outdated solutions in various industries with new products in the biotechnology industry. For example, it will help transport companies switch to biofuels instead of diesel, and construction companies to use 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 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.

Probably genetics. Dealing with genetic material, they can work in any industry related to living organisms, be it breeding or any branch of medical knowledge.

Research history

For the first time, the existence of a virus (as a new type of pathogen) was proved in 1892 by the Russian scientist D. I. Ivanovsky and others. After many years of research into diseases of tobacco plants, in a work dated 1892, D.I. Ivanovsky comes to the conclusion that tobacco mosaic is caused by "bacteria passing through the Chamberlain filter, which, however, are not able to grow on artificial substrates."

Five years later, in the study of diseases of cattle, namely foot and mouth disease, a similar filterable microorganism was isolated. And in 1898, when reproducing the experiments of D. Ivanovsky by the Dutch botanist M. Beijerinck, he called such microorganisms "filterable viruses." In abbreviated form, this name began to denote this group of microorganisms.

In subsequent years, the study of viruses played a major role in the development of epidemiology, immunology, molecular genetics, and other branches of biology. Thus, the Hershey-Chase experiment became a decisive proof of the role of DNA in the transmission of hereditary properties. Over the years, at least six more Nobel Prizes in Physiology or Medicine and three Nobel Prizes in Chemistry have been awarded for research directly related to the study of viruses.

Structure

Simply organized viruses consist of a nucleic acid and several proteins that form a shell around it - capsid. An example of such viruses is tobacco mosaic virus. Its capsid contains one type of protein with a small molecular weight. Complexly organized viruses have an additional shell - protein or lipoprotein; sometimes the outer shells of complex viruses contain carbohydrates in addition to proteins. An example of complexly organized viruses are the causative agents of influenza and herpes. Their outer shell is a fragment of the nuclear or cytoplasmic membrane of the host cell, from which the virus enters the extracellular environment.

The role of viruses in the biosphere

Viruses are one of the most common forms of existence of organic matter on the planet in terms of numbers: the waters of the oceans contain a colossal number of bacteriophages (about 250 million particles per milliliter of water), their total number in the ocean is about 4 10 30, and the number of viruses (bacteriophages) in bottom sediments of the ocean, it practically does not depend on depth and is very high everywhere. Hundreds of thousands of species (strains) of viruses live in the ocean, the vast majority of which have not been described, much less studied. Viruses play an important role in regulating the number of populations of some species of living organisms (for example, the wilding virus reduces the number of arctic foxes by several times with a period of several years).

The position of viruses in the living system

Origin of viruses

Viruses are a collective group that does not have a common ancestor. Currently, there are several hypotheses explaining the origin of viruses.

The origin of some RNA-containing viruses is associated with viroids. Viroids are highly structured circular RNA fragments replicated by the cellular RNA polymerase. It is believed that viroids are " escaped introns" - insignificant sections of mRNA cut out during splicing, which accidentally acquired the ability to replicate. Viroids do not code for proteins. It is believed that the acquisition of coding regions (open reading frame) by viroids led to the appearance of the first RNA-containing viruses. Indeed, examples of viruses containing pronounced viroid-like regions are known (Delta hepatitis virus).

Examples of structures of icosahedral virions.
A. A virus that does not have a lipid envelope (for example, picornavirus).
B. Enveloped virus (eg herpesvirus).
Numbers indicate: (1) capsid, (2) genomic nucleic acid, (3) capsomere, (4) nucleocapsid, (5) virion, (6) lipid envelope, (7) membrane envelope proteins.

Detachment ( -virales) Family ( -viridae) Subfamily ( -virinae) Genus ( -virus) View ( -virus)

Baltimore classification

Nobel laureate biologist David Baltimore proposed his classification scheme for viruses based on differences in the mechanism of mRNA production. This system includes seven main groups:

  • (I) Viruses containing double-stranded DNA and lacking an RNA stage (e.g. herpesviruses, poxviruses, papovaviruses, mimiviruses).
  • (II) Viruses containing double-stranded RNA (eg rotaviruses).
  • (III) Viruses containing a single-stranded DNA molecule (for example, parvoviruses).
  • (IV) Viruses containing a positive polarity single-stranded RNA molecule (eg picornaviruses, flaviviruses).
  • (V) Viruses containing a single-stranded RNA molecule of negative or dual polarity (eg, orthomyxoviruses, filoviruses).
  • (VI) Viruses containing a single-stranded RNA molecule and having in their life cycle the stage of DNA synthesis on an RNA template, retroviruses (for example, HIV).
  • (VII) Viruses containing double-stranded DNA and having in their life cycle the stage of DNA synthesis on an RNA template, retroid viruses (for example, hepatitis B virus).

Currently, for the classification of viruses, both systems are used simultaneously, as complementary to each other.

Further division is made on the basis of such features as the structure of the genome (the presence of segments, a circular or linear molecule), genetic similarity with other viruses, the presence of a lipid membrane, the taxonomic affiliation of the host organism, and so on.

Viruses in popular culture

In literature

  • S.T.A.L.K.E.R. (fantasy novel)

In cinema

  • Resident Evil" and its sequels.
  • In the fantasy horror film "28 Days Later" and its sequels.
  • In the plot of the disaster film " Epidemic" there is a fictional motaba virus, the description of which resembles the real Ebola virus.
  • In the movie "Welcome to Zombieland".
  • In the movie "Purple Ball".
  • In the movie "Carriers".
  • In "I Am Legend".
  • In the movie "Contagion".
  • In the film "Report".
  • In the movie Quarantine.
  • In the movie "Quarantine 2: Terminal".
  • In the series "Regenesis".
  • In the TV series The Walking Dead.
  • In the television series "Closed School".
  • In the movie "Carriers".

In animation

In recent years, viruses have often become "heroes" of cartoons and animated series, among which should be mentioned, for example, "Osmosis Jones" (USA), 2001), "Ozzy and Drix" (USA, 2002-2004) and "Virus attacks" (Italy, 2011).

Notes

  1. In English . In Latin, the question of the plural of a given word is controversial. The word lat. virus belongs to a rare variety of the II declension, words of the middle gender in -us: Nom.Acc.Voc. virus, Gen. viri, Dat.Abl. viro. Likewise, lat. vulgus and lat. pelagus; in classical Latin, the plural is recorded only in the latter: lat. pelage, a form of ancient Greek origin, where η<εα.
  2. Taxonomy of viruses at the International Committee on Taxonomy of Viruses (ICTV) website.
  3. (English))
  4. Cello J, Paul AV, Wimmer E (2002). "Chemical synthesis of poliovirus cDNA: generation of infectious virus in the absence of natural template". Science 297 (5583): 1016–8. DOI:10.1126/science.1072266. PMID 12114528 .
  5. Bergh O, Børsheim KY, Bratbak G, Heldal M (August 1989). "High abundance of viruses found in aquatic environments". Nature 340 (6233): 467–8. DOI:10.1038/340467a0. PMID2755508.
  6. Elements - science news: Destroying bacterial cells, viruses actively participate in the cycle of substances in the depths of the ocean

Carbohydrates are made up of...

carbon, hydrogen and oxygen

carbon, nitrogen and hydrogen

carbon, oxygen and nitrogen

Carbohydrates, or saccharides, - one of the main groups of organic compounds. They are part of the cells of all living organisms. Carbohydrates are made up of carbon, hydrogen and oxygen. They got their name because most of them have the same ratio of hydrogen and oxygen in the molecule as in the water molecule.

The general formula of carbohydrates: Cn (H 2 O)m. Examples are glucose- C 6 H 12 O 6 and sucrose- C 12 H 22 O 11. Other elements may also be included in the composition of carbohydrate derivatives. All carbohydrates are divided into simple, or monosaccharides, and complex, or polysaccharides. Of the monosaccharides, ribose, deoxyribose, glucose, fructose, and galactose are of greatest importance for living organisms.

Functions of carbohydrates: energy, building, protective, storage.

Determine from the proposed polysaccharides.

starch, glycogen, chitin...

glucose, fructose, galactose

ribose, deoxyribose

Di- and polysaccharides are formed by combining two or more monosaccharides. Disaccharides are similar in properties to monosaccharides. Both of them are highly soluble in water and have a sweet taste. Polysaccharides are made up of a large number of monosaccharides linked by covalent bonds. These include starch, glycogen, cellulose, chitin other.

Violation of the natural structure of the protein.

denaturation

renaturation

degeneration

Violation of the natural structure of the protein is called denaturation. It can occur under the influence of temperature, chemicals, radiant energy and other factors. With a weak impact, only the quaternary structure disintegrates, with a stronger one, the tertiary one, and then the secondary one, and the protein remains in the form of a polypeptide chain. This process is partially reversible: if the primary structure is not destroyed, then the denatured protein is able to restore its structure. Thus, all structural features of a protein macromolecule are determined by its primary structure.

The function due to which the acceleration of biochemical reactions in the cell occurs.

catalytic

enzymatic

both answers are correct

Enzymes(or biocatalysts) are protein molecules that act as biological catalysts, increasing the rate of chemical reactions thousands of times. In order for large organic molecules to react, simple contact is not enough for them. It is necessary that the functional groups of these molecules face each other and that no other molecules interfere with their interaction. The probability that the molecules themselves orient themselves in the right way is negligible. The enzyme, on the other hand, attaches both molecules to itself in the right position, helps to get rid of the water film, supplies energy, removes excess parts and releases the finished reaction product. At the same time, the enzymes themselves, like other chemical catalysts, do not change as a result of past reactions and do their work again and again. There are optimal conditions for the functioning of each enzyme. Some enzymes are active in a neutral environment, while others are active in an acidic or alkaline environment. At temperatures above 60ºС, most enzymes do not function.

The function of contractile proteins.

motor

transport

protective

Motor the function of proteins is performed by special contractile proteins. Thanks to them, cilia and flagella move in protozoa, chromosomes move during cell division, muscles contract in multicellular organisms, and other types of movement in living organisms are improved.

The flagellum of all eukaryotic cells is about 100 µm long. On the transverse section, one can see that there are 9 pairs of microtubules along the periphery of the flagellum, and 2 microtubules in the center. All pairs of microtubules are interconnected. The protein that carries out this binding changes its conformation due to the energy released during ATP hydrolysis. This leads to the fact that pairs of microtubules begin to move relative to each other, the flagellum bends and the cell begins to move.

The function of proteins, due to which hemoglobin carries oxygen from the lungs to the cells of other tissues and organs.

transport

motor

both answers are correct

It is important transport protein function. So, hemoglobin carries oxygen from the lungs to the cells of other tissues and organs. In muscles, this function is performed by the protein hemoglobin. Blood serum proteins (albumin) promote the transfer of lipids and fatty acids, various biologically active substances. By attaching oxygen, hemoglobin turns from bluish to scarlet. Therefore, blood with a lot of oxygen differs in color from blood with little oxygen. Transport proteins in the outer membrane of cells carry various substances from the environment into the cytoplasm.

The function of a protein that maintains a constant concentration of substances in the blood and cells of the body. Participate in growth, reproduction and other vital processes.

enzymatic

regulatory

transport

Regulatory function is inherent in proteins - hormones. They maintain constant concentrations of substances in the blood and cells, participate in growth, reproduction and other vital processes. In the presence of a regulatory substance, the reading of a certain section of DNA begins. The protein produced by this gene begins a long chain of transformations of substances passing through the enzymatic complex. In the end, a regulatory substance is produced that stops the reading or transfers it to another site. At the same time, it is the DNA information that determines which substances to produce, and the final product of synthesis blocks DNA and stops the entire process. Another way: DNA is blocked by a substance that appeared as a result of the activity of the body's control systems: nervous or humoral. Of course, there may be a large number of intermediaries in this chain. There is, for example, a whole group of receptor proteins that send a control signal in response to a change in the external or internal environment.

The DNA molecule contains nitrogenous bases...

adenine, guanine, cytosine, thymine

adenine, guanine, leucine, thymine

no correct answer

There are four types of nitrogenous bases in the DNA molecule: adenine, guanine, cytosine and thymine. They determine the names of the corresponding nucleotides.

Determine the composition of the nucleotide.

phosphoric acid residue, cytidine, carbohydrate

nitrogenous base, carbohydrate, DNA

nitrogenous base, carbohydrate, phosphoric acid residue

Each nucleotide consists of three components connected by strong chemical bonds. These are a nitrogenous base, a carbohydrate (ribose or deoxyribose) and a phosphoric acid residue.

The name of the bond between adenine and thymine in the formation of a double-stranded DNA molecule.

single

double

triple

The DNA molecule is a double row of nucleotides stitched in the longitudinal and transverse directions Carbohydrates, reliably linked by phosphate groups in two chains, serve as the framework of its structure. Between the "ladder" chains are nitrogenous bases attracted to each other by weak hydrogen bonds (in the case of adenine-thymine, the bond double).

Determine the composition of adenosine triphosphate:

adenine, uracil, two phosphoric acid residues

adenine, ribose, three phosphoric acid residues

Nucleic acid adenosine triphosphate(ATP) consists of a single nucleotide and contains two macroergic (energy-rich) bonds between phosphate groups. ATP is absolutely necessary in every cell, since it plays the role of a biological accumulator - an energy carrier. It is needed wherever energy is stored or released and used, that is, in almost any biochemical reaction, since such reactions occur in every cell almost continuously, each ATP molecule is discharged and charged again, for example, in the human body, on average, once every minute. ATP is found in the cytoplasm, mitochondria, plastids, and nuclei.

virus

Our review, in which cells are considered as units of living matter, cannot be complete if we do not touch on viruses. Although not alive, viruses are biologically formed supramolecular complexes that are capable of self-replication in their respective host cells. A virus consists of a nucleic acid molecule and its surrounding protective shell, or capsid, built from protein molecules. Viruses exist in two states.

Rice. 2-23. An electron micrograph of a plant cell wall. The wall consists of criss-crossing layers of cellulose fibers embedded in an organic "glue". The walls of plant cells are very strong, in their structure they resemble a concrete slab reinforced with steel reinforcement.

Rice. 2-24. Bacteriophage replication in the host cell.

Some viruses contain DNA, while others contain RNA.

Hundreds of different viruses are known to be specific for certain types of host cells. The role of hosts can be played by cells of animals, plants or bacteria (Tables 2-3). Viruses specific to bacteria are called bacteriophages, or simply phages (the word "phage" means to eat, absorb). The capsid of viruses can be built from protein molecules of only one type, as is the case, for example, in the case of tobacco mosaic virus, one of the simplest viruses, which was first obtained in crystalline form (Fig. 2-25). Other viruses may contain dozens or hundreds of different types of proteins. Virus sizes vary widely. Thus, one of the smallest viruses, bacteriophage fX174, has a diameter of 18 nm, while one of the largest viruses, the vaccinia virus, corresponds in size to the smallest bacteria. Viruses also differ in form and degree of complexity of their structure. Among the most complex is the bacteriophage T4 (Fig. 2-25), for which the host cell is E. coli. The T4 phage has a head, a process ("tail"), and a complex set of tail filaments; when viral DNA is introduced into a host cell, they act together as a "stinger" or hypodermic syringe. On fig. 2-25 and in table. 2-3 shows data on the size, shape and mass of particles of a number of viruses, as well as the type and size of their constituent nucleic acid molecules. Some viruses are unusually pathogenic to humans. These include, in particular, viruses that cause smallpox, polio, influenza, colds, infectious mononucleosis and shingles. It is believed that the cause of cancer in animals are also viruses that may be in a latent state.

Table 2-3. Properties of some viruses

Viruses play an increasingly important role in biochemical research, since they provide extremely valuable information about the structure of chromosomes, the mechanisms of enzymatic synthesis of nucleic acids, and the regulation of the transfer of genetic information.