Repair of the DNA

DNA is subjected continuously to bearing stresses reached with its integrity. These stresses are generally of chemical nature like the free radical of oxygen and the agents alkylants, or physics, like the Radiation S Ultraviolet your and the ionizing rays.

Five great systems of repair

These stresses induce chemical modifications of the bases nitrogenized of the DNA, breaks simple bit of DNA, crosslinks intrabrins and interbrins, crosslinks DNA proteins and finally of the breaks doubles bit of the DNA destroying the integrity of the chromosome thus. To answer these stresses, the cell developed complex systems enabling him to probe its DNA and, if necessary, to repair it. 5 great systems of repair exist within the cells eucaryotes:

the Base excision to repair (BER)
the Nucleotide excision to repair (NER)
the Mismatch to repair (MR.)
the Not-Counterpart End-Joining (NHEJ)
the homologous Recombination

Detection of the damage of the DNA

The cell has several " sondes" he allowing to detect the damage of the DNA. These probes are proteins (Glycosylase, PARP1, XPC, MRN, ATM and RPA) which will be able specifically to detect various deteriorations likely to occur on the DNA. Each system of repair uses its specific probes. These various probes will recognize and to fix itself at abnormal structures present within the DNA, nitrogenized basic dimer, bases nitrogenized modified, DNA and proteins cross-country race-linkés, DNA simple bit, distortion of the double helix.

Preparation of repair

Before being repaired, the faded components of the DNA must be withdrawn. Moreover when the DNA is broken, one of the bits is degraded on some nucleotides. For these various processes the cell calls upon enzymes (Glycosylase, Endonucléase and Exonucléase). The DNA marked by the probes of detection of the breaks allows the recruitment of these enzymes and the elimination of the abnormal structures or the degradation of nucleotides necessary for repair.

Synthesis of the bit of DNA allowing repair

Once the elements damages removed or after degradation of one of the two bits, the cell synthesizes a new bit of DNA while being useful like stamps simple bit remaining, even of the propeller of DNA sister not damaged. (Each area of the genome is represented by two propellers having 2 bits of DNA each one) This synthesis of DNA requires the activity of a DNA polymerase which will synthesize a new bit of DNA starting from the sequence of DNA of the nonfaded bit.

End of repair

Once the DNA damages replaced by the new one, a ligase makes it possible to weld last nucleotide synthesized by the DNA polymerase with first preserved nucleotide of the bit of initial DNA.

Simple: DNA to repair

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