The body of the virus consists of. What is a virus? What does it consist of? The position of non-cellular forms in the taxonomy of living nature

Viruses differ from inanimate matter in two properties: the ability to reproduce similar forms (multiply) and the possession of heredity and variability.

Viruses are designed very simply. Each viral particle consists of RNA or DNA enclosed in a protein shell called capsid (Fig. 16).

2. Vital activity of viruses.

Having penetrated the cell, the virus changes its metabolism, directing all its activity to the production of viral nucleic acid and viral proteins. Inside the cell, self-assembly of viral particles from synthesized nucleic acid molecules and proteins occurs. Before death, a huge number of viral particles manage to be synthesized in the cell. Ultimately, the cell dies, its shell bursts and the viruses leave the host cell (Fig. 17).

By settling in the cells of living organisms, viruses cause many dangerous diseases: in humans, influenza, smallpox, measles, polio, mumps, rabies, AIDS and many others; in plants: mosaic disease of tobacco, tomatoes, cucumbers, leaf curl, dwarfism, etc.; in animals - foot and mouth disease, swine and bird plague, infectious anemia of horses, etc.

Questions for the test in the section “Molecular level of living nature”

Each option will be asked 10 questions
Each question must be answered in one complete sentence.

1. What elements are included in carbohydrates? Write down the general formula for carbohydrates.
2. What carbohydrates are part of nucleic acids (DNA and RNA)?
3. Write down the names of the most important disaccharides.
4. Write down the names of the most important polysaccharides.
5. What polysaccharides make up the cell walls of plant and fungal cells?
6. What carbohydrates accumulate in plant and animal cells as reserve substances?
7. Write down the general formula of an amino acid.
8. What are the primary and secondary structures of proteins?
9. What are the tertiary and quaternary structures of proteins?
10. What is denaturation?
11. What molecules are classified as biopolymers?
12. What are enzymes?
13. What is the name of the region of the enzyme that interacts with the substrate molecule?
14. Where are DNA molecules found in a cell?
15. What nitrogenous bases make up DNA nucleotides? RNA?
16. How many hydrogen bonds are formed between complementary nitrogenous bases in DNA?
17. What functions do DNA and RNA perform in a cell?
18. What carbohydrates are part of DNA nucleotides? RNA?
19. What organic molecules, besides proteins, have catalytic activity?
20. What types of RNA are there in a cell?
21. Where are RNA molecules found in a cell?
22. What molecules do fats consist of?
23. How much energy is released from the oxidation of fat compared to carbohydrates?
24. What molecules are the custodians of genetic information?
25. What molecules are the main building blocks of cells? Main and backup energy source?
26. What carbohydrate and what nitrogenous base are included in ATP?
27. How much energy is released during the breakdown of ATP to AMP and 2 H molecules 3 RO 4 ?
28. Why does the body need vitamins for normal metabolism?
29. What nucleic acids can be found in viruses?
30. List 5 human diseases caused by viruses.

History of research

The existence of a virus (as a new type of pathogen) was first proven 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 Chamberlant filter, which, however, are not able to grow on artificial substrates.”

Five years later, while studying 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 vital role in the development of epidemiology, immunology, molecular genetics and other branches of biology. Thus, the Hershey-Chase experiment became decisive evidence of the role of DNA in the transmission of hereditary properties. 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 the 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. Examples of complexly organized viruses are the pathogens of influenza and herpes. Their outer shell is a fragment of the nuclear or cytoplasmic membrane of the host cell, from which the virus exits into 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 world's 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 practically does not depend on depth and is very high everywhere. The ocean is home to hundreds of thousands of species (strains) of viruses, the vast majority of which have not been described, much less studied. Viruses play an important role in regulating the population size of some species of living organisms (for example, the wilding virus reduces the number of arctic foxes several times over 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 viruses is associated with viroids. Viroids are highly structured circular RNA fragments that are 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 encode proteins. It is believed that the acquisition of coding regions (open reading frame) by viroids led to the appearance of the first RNA viruses. Indeed, there are known examples of viruses containing pronounced viroid-like regions (hepatitis Delta virus).

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

Baltimore classification

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

• (I) Viruses that contain double-stranded DNA and do not have an RNA stage (for example, herpesviruses, poxviruses, papovaviruses, mimivirus).
• (II) Double-stranded RNA viruses (eg rotaviruses).
• (III) Viruses containing a single-stranded DNA molecule (eg, parvoviruses).
• (IV) Viruses containing a single-stranded RNA molecule of positive polarity (for example, picornaviruses, flaviviruses).
• (V) Viruses containing a single-stranded RNA molecule of negative or double polarity (for example, 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, both systems are used simultaneously to classify viruses, as complementary to each other.

Further division is made on the basis of such characteristics as genome structure (presence of segments, circular or linear molecule), genetic similarity with other viruses, the presence of a lipid membrane, 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 science fiction horror film “28 Days Later” and its sequels.
• The plot of the disaster film "Epidemic" features a fictional virus "motaba", the description of which is reminiscent of the real Ebola virus.
• In the movie "Welcome to Zombieland".
• In the film "The Purple Ball".
• In the film "Carriers".
• In the film "I am Legend".
• In the film "Contagion".
• In the film "Report".
• In the movie "Quarantine".
• In the movie "Quarantine 2: Terminal".
• In the series "Regenesis".
• In the television series "The Walking Dead".
• In the television series "Closed School".
• In the film "Carriers".

In animation

In recent years, viruses have often become the “heroes” of cartoons and animated series, among which are, for example, “Osmosis Jones” (USA), 2001), “Ozzy and Drix” (USA, 2002-2004) and “The Virus Attacks” (Italy, 2011).

Notes

1. In English . In Latin, the question of the plural of this word is controversial. The word is lat. virus belongs to a rare variety of the II declension, neuter words in -us: Nom.Acc.Voc. virus, Gen. viri,Dat.Abl. viro. Lat is also inclined. vulgus and lat. pelagus; in classical Latin the plural is fixed 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. PMID 2755508.
6. Elements - science news: By destroying bacterial cells, viruses actively participate in the circulation of substances in the depths of the ocean

The molecular level is the initial, deepest level of organization of living things. Each organism consists of molecules of organic substances found in a cell - these are biological molecules. Living organisms consist of the same chemical elements as non-living ones. Currently, more than 100 elements are known, most of them are found in living organisms. The most common in living nature: carbohydrate (C), oxygen (O), hydrogen (H) and nitrogen (N). The basis of all organic compounds is carbon, it enters into bond with many atoms and their groups - forms chains that differ in chemical composition, length and shape.

Monomers - groups of atoms, relatively simply structured, part of complex chemical compounds Polymer - a chain consisting of numerous links - monomers Biopolymers - polymers that are part of living organisms A polymer molecule consists of thousands of interconnected monomers (identical or different) Properties of biopolymers depend on: the structure of monomers the number of monomers the variety of monomers Biopolymers are universal, because built according to the same plan for all living organisms.

Our review, which considers cells as units of living matter, cannot be complete without touching on viruses. Although viruses are not living, they 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 a surrounding protective shell, or capsid, made of protein molecules. Viruses exist in two states.

Rice. 2-23. Electron micrograph of a plant cell wall. The wall consists of intersecting layers of cellulose fibers immersed in an organic “glue”. The walls of plant cells are very strong; their structure resembles 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 that are specific for certain types of host cells. The role of hosts can be played by animal, plant or bacterial cells (Table 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 the tobacco mosaic virus - one of the simplest viruses, which was the first to be obtained in crystalline form (Fig. 2-25). Other viruses may contain tens or hundreds of different types of proteins. The sizes of viruses 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 in its particles. Viruses also differ in shape and degree of complexity of their structure. Among the most complex is bacteriophage T4 (Fig. 2-25), for which E. coli serves as the host cell. Phage T4 has a head, an appendage (“tail”), and a complex set of tail filaments; when injecting viral DNA into a host cell, they act together as a "sting" or hypodermic syringe. In Fig. 2-25 and in table. Tables 2-3 show data on the size, shape and mass of particles of a number of viruses, as well as the type and size of the nucleic acid molecules included in their composition. Some viruses are unusually pathogenic for humans. These include, but are not limited to, the viruses that cause smallpox, polio, influenza, colds, infectious mononucleosis, and herpes zoster. It is believed that cancer in animals is also caused by viruses, which can be in a latent state.

Table 2-3. Properties of some viruses

Viruses are playing an increasingly important role in biochemical research, since with their help it is possible to obtain 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.

Representatives of the kingdom of viruses are a special group of life forms. They not only have a highly specialized structure, but are also characterized by a specific metabolism. In this article we will study a non-cellular life form - a virus. What it consists of, how it reproduces and what role it plays in nature, you will find out by reading it.

Discovery of non-cellular life forms

In 1892, the Russian scientist D. Ivanovsky studied the causative agent of tobacco disease - tobacco mosaic. He established that the pathogenic agent is not a bacteria, but is a special form, later called a virus. At the end of the 19th century, high-resolution microscopes were not yet used in biology, so the scientist could not find out what molecules the virus consists of, as well as see and describe it. After the creation of the electron microscope at the beginning of the 20th century, the world saw the first representatives of the new kingdom, which turned out to be the cause of many dangerous and difficult-to-treat diseases of humans, as well as other living organisms: animals, plants, bacteria.

The position of non-cellular forms in the taxonomy of living nature

As mentioned earlier, these organisms are combined into a fifth - viruses. The main morphological feature characteristic of all viruses is the absence of a cellular structure. Until now, discussions continue in the scientific world on the question of whether non-cellular forms are living objects in the full sense of this concept. After all, all manifestations of metabolism are possible in them only after penetration into a living cell. Until this moment, viruses behave like objects of inanimate nature: they do not have metabolic reactions, they do not reproduce. At the beginning of the 20th century, scientists faced a whole group of questions: what is a virus, what does its shell consist of, what is inside the viral particle? The answers were obtained as a result of many years of research and experimentation, which served as the basis for a new scientific discipline. It arose at the intersection of biology and medicine and is called virology.

Structural features

The expression “everything ingenious is simple” directly applies to non-cellular life forms. The virus consists of nucleic acid molecules - DNA or RNA, coated with a protein shell. It does not have its own energy and protein-synthesizing apparatus. Without a host cell, viruses do not have a single sign of a living substance: no respiration, no growth, no irritability, no reproduction. For all this to appear, only one thing is required: to find a victim - a living cell, subordinate its metabolism to its nucleic acid and ultimately destroy it. As mentioned earlier, the virus shell consists of protein molecules that have an ordered structure (simple viruses).

If the shell also includes lipoprotein subunits, which are actually part of the cytoplasmic membrane of the host cell, such viruses are called complex viruses (the causative agents of smallpox and hepatitis B). Often the surface shell of the virus also includes glycoproteins. They perform a signaling function. Thus, both the shell and the virus itself consist of molecules of an organic component - protein and nucleic acids (DNA or RNA).

How viruses penetrate living cells

The result of a pathogen attack on a cell is the combination of DNA or RNA of the virus with its own protein particles. Thus, the newly formed virus consists of nucleic acid molecules coated with ordered protein particles. The host cell membrane is destroyed, the cell dies, and the viruses that emerge from it invade healthy cells of the body.

The phenomenon of reverse reduplication

At the beginning of the study of representatives of this kingdom, there was an opinion that viruses consist of cells, but D. Ivanovsky’s experiments proved that pathogens cannot be isolated using microbiological filters: pathogens passed through their pores and ended up in the filtrate, which retained virulent properties.

Further research established the fact that the virus consists of molecules of organic matter and shows signs of a living substance only after its direct penetration into the cell. In it he begins to multiply. Most contain RNA as described above, but some, such as the AIDS virus, cause DNA synthesis in the host cell nucleus. This phenomenon is called reverse replication. Then the viral mRNA is synthesized on the DNA molecule, and the assembly of viral protein subunits that form its shell begins on it.

Features of bacteriophages

What is a bacteriophage - a cell or a virus? What does this non-cellular life form consist of? The answers to these questions are as follows: it affects exclusively prokaryotic organisms - bacteria. Its structure is quite unique. The virus consists of molecules of organic matter and is divided into three parts: the head, the stem (case) and the tail threads. In the front part - the head - there is a DNA molecule. Next comes the case, which has a hollow rod inside. The tail filaments attached to it ensure the connection of the virus with the receptor loci of the bacterial plasma membrane. The principle of operation of the bacteriophage resembles a syringe. After contraction of the sheath proteins, the DNA molecule enters the hollow rod and is further injected into the cytoplasm of the target cell. Now the infected bacterium will synthesize the DNA of the virus and its proteins, which will inevitably lead to its death.

How the body protects itself from viral infections

Nature has created special protective devices that resist viral diseases of plants, animals and humans. The pathogens themselves are perceived by their cells as antigens. In response to the presence of viruses in the body, immunoglobulins are produced - protective antibodies. The organs of the immune system - the thymus, lymph nodes - respond to viral invasion and contribute to the production of protective proteins - interferons. These substances inhibit the development of viral particles and inhibit their reproduction. Both types of protective reactions discussed above relate to humoral immunity. Another form of protection is cellular. Leukocytes, macrophages, neutrophils absorb viral particles and break them down.

The meaning of viruses

It's no secret that it is mostly negative. These ultra-small pathogenic particles (from 15 to 450 nm), visible only with an electron microscope, cause a whole bunch of dangerous and intractable diseases of all organisms existing on Earth without exception. Thus, they affect vital organs and systems, such as the nervous (rabies, encephalitis, polio), immune (AIDS), digestive (hepatitis), respiratory (influenza, adenoinfections). Animals suffer from lizards and plague, and plants suffer from various necroses, spots, and mosaics.

The diversity of representatives of the kingdom has not been fully studied. The proof is that new types of viruses are still being discovered and previously unknown diseases are being diagnosed. For example, in the mid-20th century, the Zika virus was discovered in Africa. It is found in the body of mosquitoes, which, when they bite, infect humans and other mammals. Symptoms of the disease indicate that the pathogen primarily affects parts of the central nervous system and causes microcephaly in newborns. People who are carriers of this virus should remember that they pose a potential danger to their partners, since cases of sexual transmission of the disease have been reported in medical practice.

The positive role of viruses includes their use in the fight against pest species and in genetic engineering.

In this work, we explained what a virus is, what its particle consists of, and how organisms protect themselves from pathogenic agents. We also determined what role non-cellular life forms play in nature.