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Under cellular death or lethal effect of radiation exposure one understands the loss by a cell|cell| the ability to|to| proliferation|. The survived cells |cells|are those ones, which preserved the ability to|to| unlimited reproduction|duplication|, which is cloning|. Thus|on this grow|, the question is about the reproductive| death of a cell|cell|. This form|shape| of radio-inactivation| of cells|cells| is most widespread in nature.
Another type of the reproductive| death of the exposed cells descendants |cells| is the formation of the so-called giant cells|cells|, which arise up as a result of the confluence of two neighbouring|nearby|, “sisterly” cells|cells|. Such cells|cells| are able to 2-3 divisions|clever|, after which they perish.
The principal reason for the reproductive| death of cells|cells| is|appears| structural interaction|conversions| of DNA| as the so-called chromosomal alterations|realignments| or aberations|. The basic|main| types of aberrations are|: fragmentation of chromosomes, forming of chromosomal bridges, dicentrics|, circular chromosomes, the appearance of intra-| and interchromosomal exchanges, and others.
Some|certain| aberration, for example bridges, mechanically|mechanics| hinder|prevents| the division of cells|cell|. The exchange inside chromosomes and between them results in|to| the uneven division|distributing| of chromosomes, |by| the loss of the genetic material|fabric| that causes|calls| the death of a cell|cell| as a result of metabolites deficite|, the synthesis of which|what| was encoded by the DNA| of the lost part|portion| of the chromosome.
Still another form|shape| of radiation of cells inactivation| |cells| - the interphase| death – sets at the cells|cells| entering mitosis|. At the radiation exposure doses 10 Gy| death can set in “under a ray|beam|” or soon|before long| after radiation exposure. At the radiation exposure dose up to 10 Gy| death sets in within first hours after radiation exposure and can be registered as the varied|various| degenerative changes|changing| of cells|cell| - more frequent piknosis or fragmentation of chromatin|.
The nature of the cells radiation death|cells|
The sensitiveness of a cell|cell| nucleus is approximately six orders higher than the sensitiveness of protoplasm. Of all intranuclear structures DNA| is accountable for the viability of a cell|cell||appears|. The latter takes part in forming chromosomes and the transfer of the genetic information. Radiation exposure causes|calls| varied|various| interaction|conversions| in DNA|: breaks of a DNA molecule|, the formation of alkali-labile associations|, the loss of bases|grounds| and change|changing| of their composition|syllable,storage|, changes|changing| of nucleotides| sequences, sewings together of DNA|-DNA| and DNA|-protein, violations of DNA| complexes with other molecules.
One distinguishes single breaks of DNA|, when the associations | between separate atomic groupments is violated|excited| in one of the filaments|threads,strings| of a bi-spiral| molecule of DNA| and double, when the break takes place at once|immediately| near the closely|near| located areas of two chains, that results in|to| the disintegration of a molecule. At any|some| break, reading the information from a molecule of DNA and spatial structure of chromatin are violated|excited
Single breaks do not result in|to| breakages of a molecule of DNA|, because the torn filament|thread,string| is firmly|tightly| kept |retained,maintained,deducted| in place by hydrogen, hydrophobic| and other types of interaction and the opposite filament|thread,string| of DNA|. In addition, the structure is restored well enough |restored| by the powerful system of reparation|. Single breaks themselves are|appears| not the reasons for cells destruction|cells|. With the increase of the radiation exposure dose the probability of transition of single breaks into double ones grows as well.Rare-ionising| radiations(gamma, x-ray, fast|quick,fast| electrons) per 20-100 single breaks cause one double break. Densly-ionising| radiations cause the|calls| much greater|far more| number of double breaks of DNA| and chromosomes aberations| immediately|immediately| after radiation exposure. Alongside with the formation of breaks, the structure of bases|grounds| in the exposed DNA|, foremost|first and foremost,first off| of thimine is violated |, that increases the number of genes mutations|excited|. The formation of sewings together between DNA| and proteins of a nucleoprotein| complex is marked|noted|. Finally, the important sequence of radiation exposure is the change|changing| of epigenomic| (unconnected with the enuclear material|fabric|) heredity of a cell|cell| the transmitters|carriers| of which|what| are|appears| varied|various| cytoplasmic| organels||appears|. Thus, the functional activity of the exposed cells descendants |cells| goes down. Probably, exactly it can be one of the reasons|causes| for remote|distant| consequences of radiation exposure. However, the main|head,leading| reason of the cells reproductive| death |cells| at radiation exposure is|appears| the damage of their genetic apparatus. The post-radiation renewal (reparatiion|) of cells|cells| A lot of radiation damages recommence|restored|. Such damages are named|calls| potential. Their fate|stake,share| may be relateed to two ways: they are repaired| and then a cell|cell| survives, or realized and then a cell|cell| perishes. After the time of realization, one distinguishes the pre-replicative|, post-replicative | and replicative | reparations|. The pre-replicative| reparatiion| (before the |by|stage of DNA doubling|) can take place by the reunion of breaks, and also with the help of exclusion|withdrawal,exclusion| (excision|) of the damaged bases|grounds|. In the uniting of single breaks there take part the enzymes: ligase|, endo-|, exonuclease|, DNA-ligase|, which|what| provide|secures| the eventual|end,final| act of reparation| - the ligasion| reunion. The post-replicative | reparatiion| is the process at which|what| a cell|cell| keeps its |saves,stores| viability, inspite of the presence of DNA defects |. The replicative | reparatiion| (DNA renewal | in the process of its reparation|) is carried out by eliminating during reparation| of damages in the area|zone| of chain growth point|heig, or by elongation|, passing the damage.
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