36 The interaction of the virus with the cell. Reproduction of viruses.

The interaction is a common biological system at the genetic level.

There are four types of interaction:

1) a productive viral infection (interaction, which results in the reproduction of the virus and the cells die);

2) abortive viral infection (interaction, in which viral replication does not occur, and the cell restores the distributed function);

3) latent viral infection (the virus is a reproduction, and the cell retains its functional activity);

4) the virus-induced transformation (interaction, in which a cell that is infected with a virus, taking on new, previously inherent properties).

After the adsorption virions penetrate through endocytosis (viropeksisa) or as a result of the merger of viral and cellular membranes. Formed vacuoles containing whole virions or internal components fall into lysosomes where

deproteinization carried out, ie, the "stripping" of the virus, resulting in viral proteins are destroyed. The liberated nucleic acids from proteins by the virus enters the cell channel into the cell nucleus, or remain in the cytoplasm.

The nucleic acids of viruses implement a genetic program to create viral progeny and determine the genetic properties of viruses. With the help of special enzymes (polymerases) make copies of the parent nucleic kitty items (replication occurs), and synthesized messenger RNAs that bind to ribosomes and synthesize viral proteins subsidiaries (translation).

Once in the infected cell accumulates enough components of the virus, begins assembling progeny virions. This process usually takes place near the cell membrane, which sometimes take a direct part in it. As part of the newly formed virions are frequently found substances characteristic of the cells in which the virus multiplies. In such cases, the final step of forming virions is blocked enveloping layer of the cell membrane.

The last stage of the interaction of viruses with cells is the way out of the cell or release of daughter viral particles. Simple viruses lacking superkapsid cause degradation of the cells and fall into the intercellular space.

Other viruses that have a lipoprotein envelope out of the cells by budding. In this case, the cell remains viable for a long time. In some cases, viruses accumulate in the cytoplasm or the nucleus of infected cells, forming a crystal-like clusters - inclusion bodies.

37. Bacteriophages. Types of morphology. The chemical composition.

Bacteriophages (from 'bacteria' and Greek. Phagos - eater) - Viruses

of bacteria having the ability to specifically penetrate bacterial cells reproduce them and cause their dissolution (lysis).

Bacteriophages are widely distributed in nature. They are found in water, soil, food products, various secretions of humans and animals,is, where there are bacteria. At present, these viruses were detected in the majority bacteria disease-causing as well as no disease, as well as a number of other organisms (eg fungi). Therefore, in the broadest sense of the word, they were called simply phages. Phages vary in shape, structural organization, type and nature of the nucleic acid interactions with microbial cell.

Morphology. Most phages under the electron microscope, have the shape of a tadpole or sperm, some - cubic or filamentous form. Dimensions phages range from 20 to 800 nm in filamentous phages. The best studied large bacteriophages shaped sperm. They consist of an elongated icosahedral head size 65 -100 nm and tail ridge longer than 100 nm. Inside the caudal ridge has a hollow shaft in communication opening the head outside Sheath capable of reducing such as. muscle. The caudal ridge ends hexagonal basal plate with short spines, which depart from the filamentous structure - the fibrils

There are also phages having the long arm, Case is not able to contract, phages with short processes, analogous processes, no process. The chemical composition. Phages are composed of two major chemical components - a nucleic acid (DNA or RNA) and proteins. In phage-shaped sperm double-stranded DNA is densely packed in a spiral inside the head. Proteins included in the shell (capsid) surrounding the nucleic acid and all the structural elements of the tail bone. Phage structural proteins differ in composition polypeptides and represented a plurality of identical subunits arranged along a spiral type or cubic symmetry. In structural proteins, some phages detected internal (genomic) proteins associated with the nucleic acid and enzyme proteins involved in the interaction of the phage to the cell.

Resistance. Phages are more resistant to chemical and physical factors than bacteria. A number of disinfectants (phenol, ethanol, ether and chloroform) have no significant effect on the phages. Phages are highly sensitive to formalin and acids.

Inactivation of most phages occurs at a temperature of 65 - 70 ° C. For a long time, they are saved by drying in sealed ampoules, freeze at a temperature of -185 ° C in glycerol.

38. The types of interaction of phage with the bacterial cell. Lysogenicity.

Phage interaction with the bacterial cell. On the mechanism of interaction distinguish virulent and temperate phages. Virulent phages penetrated into the bacterial cell independently reproduced therein and cause lysis of the bacteria. The interaction of bacteria with virulent phage proceeds in several stages and is similar to the interaction of human and animal viruses in the host cell. However, the phage tail appendage with the shrinking cover, it has the features. These phages are adsorbed on the surface of bacterial cells by fibrils tail bone. As a result, activation of the phage enzyme ATPase is a reduction of the tail sheath process and the introduction of the rod into the cell. During the "piercing" bacterial cell wall enzyme lysozyme participates on the end of the tail bone. Subsequently, the phage DNA contained in the die cavity extends through tail rod and vigorously injected into the cytoplasm. The rest of the structural elements of the phage (capsid and process) remain outside the cell.

After biosynthesis phage components and their self-assembly into a bacterial cell accumulates to 200 new phage particles. Under the action of the phage lysozyme and intracellular osmotic pressure causes the destruction of the cell wall, yield progeny phage environment and lysis of bacteria. One lytic cycle (since the adsorption of the phage prior to their release from cells) continues for 30 - 40 min. Bacteriophage process goes through several cycles until lysed all

sensitive to this phage bacteria.

The reaction of phages with the bacterial cell characterized by a certain degree of specificity. By action specificity distinguishes multivalent phages capable of interacting with related bacterial species, monovalent phage that interact with a certain type of bacteria and phages model interacting with individual variations (types) of this bacterial species.

Temperate phages lyse not all cells in the population, with some of them they come in symbiosis, whereby the phage DNA integrates into the bacterial chromosome. In this case, the phage genome known as a prophage.

Prophage, which became part of the chromosome of the cell, with its reproduction is replicated synchronously with the genome of the bacteria without causing lysis, and handed down from one cell to an unlimited number of offspring.

Biological phenomenon of symbiosis microbial cells with moderate phage (prophage) is lysogenic, and the culture of bacteria containing a prophage, called lysogenic. This name (from the Greek. Lysis - decomposition, genea - origin) reflects the ability of prophage spontaneously or under the influence of a number of physical and chemical factors excluded from the chromosome of the cell and move to the cytoplasm, that is, to behave as a virulent phage lysis bacteria.

Lysogenic culture in its basic properties are not different from the original, but they are immune to reinfection homologous or closely related phage and, moreover, acquire additional properties that are controlled by the gene of prophage. Changing the properties of micro-organisms under the influence of prophage was called phage conversion. The latter occurs in many species of microorganisms and for their different properties: cultural, biochemical, toxigenic, antigenic, sensitivity to antibiotics, etc.

In addition, moving from an integrated state in a virulent form, temperate phage can capture a portion of the chromosome and cell lysis at last brings this part of the chromosome to another cell. If the microbial cell becomes lysogenic, it will acquire new properties. Thus, temperate phages are a powerful factor in the variability of microorganisms.

Temperate phages can be harmful microbiological production. Thus, if the microorganisms are used as producers of vaccines, antibiotics, foodstuffs and other biological substances are lysogenic danger exists transition temperate phage virulent form, will inevitably lead to lysis of the production strain.