The virus consists of molecules of organic matter and... What is a virus? What does it consist of? Viruses in popular culture
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.
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.
Carbohydrates consist of...
carbon, hydrogen and oxygen
carbon, nitrogen and hydrogen
carbon, oxygen and nitrogen
Carbohydrates, or saccharides, is 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 a water molecule.
The general formula of carbohydrates is Cn (H 2 O)m. Examples include glucose- C 6 H 12 O 6 and sucrose- C 12 H 22 O 11. Carbohydrate derivatives may also contain other elements. All carbohydrates are divided into simple, or monosaccharides, and complex, or polysaccharides. Of the monosaccharides, the most important for living organisms are ribose, deoxyribose, glucose, fructose, and galactose.
Functions of carbohydrates: energy, construction, protective, storage.
Identify polysaccharides from those given.
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 are highly soluble in water and have a sweet taste. Polysaccharides consist of a large number of monosaccharides joined by covalent bonds. These include starch, glycogen, cellulose, chitin and others.
Violation of the natural structure of the protein.
denaturation
renaturation
degeneration
Violation of the natural structure of a 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, and then the secondary, 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.
A function that accelerates biochemical reactions in the cell.
catalytic
enzymatic
both answers are correct
Function of contractile proteins.
motor
transport
protective
The flagellum of all eukaryotic cells is about 100 µm long. In a cross section, you 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 performs 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, thanks 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 function of proteins. Thus, hemoglobin carries oxygen from the lungs to the cells of other tissues and organs. In muscles, this function is performed by the protein hemoglobin. Serum proteins (albumin) promote the transfer of lipids and fatty acids and various biologically active substances. By adding oxygen, hemoglobin changes from bluish to scarlet. Therefore, blood that has a lot of oxygen is different in color from blood that has little of it. Transport proteins in the outer membrane of cells transport 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
The DNA molecule contains nitrogenous bases...
adenine, guanine, cytosine, thymine
adenine, guanine, leucine, thymine
there is no right answer
The DNA molecule contains four types of nitrogenous bases: 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. It is 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 direction. The framework of its structure is carbohydrates, securely connected by phosphate groups in two chains. Between the “ladder” chains there 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 battery - 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 recharged, for example, in the human body on average once every minute. ATP is found in the cytoplasm, mitochondria, plastids and nuclei.
virus
Part A tasks. Choose one correct answer from the four proposed
A1. The lowest level of organization of living things is:
1) atomic
2) cellular
3) molecular
4) organismic
A2. Among the listed substances it is not a biological polymer:
2) glucose
3) glycogen
4) hemoglobin
A3. The inorganic substances of the cell are:
1) carbohydrates and fats
2) nucleic acids and water
3) proteins and fats
4) water and mineral water
A4. Organic substances of a cell that ensure the storage of hereditary information and its transmission to descendants, the basis of its genetic apparatus:
3) carbohydrates
4) nucleic acids
A5. Of the listed carbohydrates, a monosaccharide is:
2) starch
3) sucrose
4) fructose
A6. Lipid molecules consist of:
1) amino acid
2) monosaccharides
3) water and minerals
4) glycerol and higher fatty acids
A7. Compared to the oxidation of 1 g of carbons, the oxidation of fats of the same mass produces energy:
1) less than half
2) twice as much
3) four times more
4) the same amount
A8. Organic substances, which are the main building material of cell structures and take part in the regulation of its vital processes, are:
1) proteins
3) carbohydrates
4) nucleic acids
A9. The whole variety of proteins is formed due to different combinations in their molecules:
1) 4 amino acids
2) 20 amino acids
3) 28 amino acids
4) 56 amino acids
A10. The highest level of spatial structural configuration of the hemoglobin molecule:
1) primary
2) secondary
3) tertiary
4) quaternary
A11. The monomers of nucleic acid molecules are:
1) nucleotides
2) monosaccharides
3) amino acids
4) higher fatty acids
A12. DNA contains sugar:
2) glucose
3) fructose
4) deoxyribose
A13. Indicate a pair of complementary nucleotides in a DNA molecule:
2) A-T
A14. For the DNA region ACCGTAATG, indicate the complementary strand:
1) AAGGTCAGT
2) TGGCTAACC
3) TCTGTTATCG
4) TGGCATTATS
A15. ATP contains:
1) ribose, adenine, three phosphoric acid residues
2) ribose, adenine, one phosphoric acid residue
3) ribose, deoxyribose, three phosphoric acid residues
4) deoxyribose, adenine, three phosphoric acid residues
A16. ATP plays an important role in the metabolism of organisms because:
1) is the structural basis of nucleotides
2) contains microenergy connections
3) is usually the end product of metabolism
4) it can be quickly obtained from the environment surrounding the body
A17. Water-soluble vitamins include:
2) C
A18. By chemical composition, most enzymes are:
2) proteins
3) carbohydrates
4) nucleic acids
2) viruses
3) bacteria
4) unicellular plants
A20. Viruses consist of:
1) cellulose membrane, cytoplasm, nucleus
2) protein shell and cytoplasm
3) nucleic acid and protein shell
4) several microscopic cells
Part B tasks. Choose three correct answers from the six proposed
IN 1. The DNA molecule differs from mRNA in that:
1) it is rolled into a spiral
2) consists of two polynucleotide chains
3) consists of one polynucleotide chain
4) has the ability to self-double
5) does not have the ability to self-double
6) serves as a template for the assembly of a polypeptide chain
AT 2. Carbohydrates have the following functions:
1) signal
2) structural
3) transport
4) regulatory
5) energy
6) enzymatic
Match the contents of the first and second columns
AT 3. Match the organic substance and the function it performs in the cell and/or in the body
A b V G d 5 1 4 2 3
Establish the correct sequence of biological processes, phenomena, practical actions
AT 4. Establish the sequence of formation of the structure of the hemoglobin protein molecule
a) twisting of protein molecules into a helix
b) the formation of peptide bonds between amino acids and the formation of a peptide chain
c) the union of several globules
d) twisting the protein molecule into a ball
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 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.
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 individual 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.