REPRODUCTION AND PROPERTIES OF VIRUSES

1. Because viruses have their own genome, they are capable of reproduction, but viruses do not multiply in the same way as other organisms (there is no binary division), but are reproduced at the expense of one NK.

2. Virus multiplication takes place inside a living host cell. They are characterized by a special form of reproduction - disjunctive (disconnected) reproduction. This means that the nucleic acids and protein subunits are synthesized by the host cell separately in different parts of the cell, after which they are self-assembled.

3. Reproduction of viruses inside the cell proceeds in several stages:

1) Adsorption - attachment of viruses to the cell surface at specific sites - receptors (their chemical nature is different: lipoproteins, glycoproteins, glycolipids). To interact with receptors, viruses also have special surface structures (spike-like outgrowth, villi, filaments) that specifically recognize and interact with the receptors of the cell. The correspondence of receptors and surface structures of the virus determines: a) the sensitivity of the organism to this virus; b) the spectrum of cells that are affected by this virus. Thus, in viruses (unlike bacteria) there is a certain (constant and limited) circle of animals, plants, bacteria that they infect.

2) Penetration into the cell - viruses penetrate into the cell in two ways: a) by pinocytosis - a pinocytic vacuole is formed; this path is typical for many viruses; b) by fusion of the viral envelope with the cell membrane; is typical for picorn and herpesviruses.

3) Disintegration ("stripping") - removal of protective shells and release of ND. The viral particle breaks down into NK and proteins. As a result, the virus can not be detected in the cell by any sensitive methods, it seems to disappear, dissolves. This phenomenon is called eclipse - "eclipse".

4) Replication of viral NK and the synthesis of viral proteins - the released viral NK leads all events in the cell: it suppresses the own metabolism of the host cell, "forces" the cellular enzymes to synthesize NK and proteins that make for the construction of new viral particles. For replication (biosynthesis of DNA or RNA), transcription (biosynthesis of mRNA through matrix DNA) and translation (biosynthesis of structural and enzymatic viral proteins): a) enzymes of the host cell; b) virion enzymes; c) virus-induced enzymes.

5) Assembling (morphogenesis) of the virion - viral NA and proteins specifically "recognize" each other and at a sufficient concentration self-assembly occurs as a result of the formation of hydrophobic, salt and hydrogen bonds.

6) The output of the virion from the cell - viral particles come out either: a) simultaneously through the holes in the cell membrane; while the cell dies (lysed); typical for simple viruses; b) by budding; In this case, a supercapsid of complex viruses is formed, which includes the chemical components of the host cell; The cell does not die and can produce viruses for a long time, preserving vitality.

The time of reproduction of viruses is from 5-6 hours (influenza virus, smallpox) to several days (measles virus, adenoviruses).

4. Several types of virus-cell interaction can be distinguished:

a) productive type - active reproduction with the release of the virus from the cell;

b) abortive type - the formation of virions is suddenly interrupted at the stage of NK replication, protein synthesis or morphogenesis;

c) Virogenia - integration (integration) of NA virus into the DNA of the cell and further their joint replication, i.e. the viral genome functions as an integral part of the cellular genome (oncogenic viruses, hepatitis B virus, adenoviruses, herpes virus). The built-in virus is called DNA-provirus. As a result, the cell acquires a number of new properties (autoimmune chronic diseases, tumors may occur). Under the action of various physical factors, DNA-provirus can be excised from the chromosome, after which it is included in the usual cycle of reproduction.

5. Viruses are sensitive to high temperatures, to UV rays, to acids and alkalis. They are damaged by such substances as potassium permanganate, formalin, mercuric chloride, alcohol. Some viruses (a poliovirus agent) are not sensitive to phenol, so it is not used in virological laboratories for disinfection. Some dyes (methylene blue, etc.) have a disastrous effect on a number of viruses.

Viruses tolerate low temperatures (optimal storage temperature is -70C). Long stored in the frozen state (at -180? C). Freezing and thawing does not affect the viability of viruses. Most viruses tolerate drying well (the foot and mouth disease virus in the dried form is stored for 6 months at room temperature), especially drying under vacuum from the frozen state. This method is called lyophilization. It is widely used to preserve live viral vaccines (the exception is the polio virus). Viruses for months remain viable in a 50% solution of glycerol, so it is widely used for conservation. Viruses carry high pressure (several thousand atmospheres) without changing the viability and are resistant to the action of proteolytic enzymes, so trypsin is very often used to purify viral vaccines (for example, smallpox vaccine) from ballast (protein) substances.

With respect to ether and deoxycholate, all viruses are divided into sensitive and insensitive, which is determined by the presence or absence of lipids in the supercapsid.

In general, it can be said that viruses differ significantly in their resistance to harmful effects. It should be remembered that in the pure culture of the virus there is always an admixture of tissue protein. And the greater stability of the virus can depend on the type of impurity.

Environmental factors (habitat) have a powerful effect on viruses and cause the variability of their traits transmitted by inheritance.

 

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