Mismatchreparaatiojärjestelmät

Mismatchreparation is a cellular mechanism that corrects errors occurring during DNA replication. These errors, known as mismatches, arise when an incorrect base is incorporated into the newly synthesized DNA strand. The mismatch repair system identifies and removes these incorrect bases, replacing them with the correct ones, thereby maintaining the integrity of the genome.

The process typically involves a series of proteins that scan the DNA for distortions caused by mismatched base pairs. Once a mismatch is detected, a repair complex is assembled. This complex excises a segment of the newly synthesized strand that contains the error. The subsequent gap is then filled in by a DNA polymerase using the original, undamaged strand as a template. Finally, a DNA ligase seals the nick in the DNA backbone.

In many organisms, mismatch repair systems distinguish between the parental and newly synthesized DNA strands. This is crucial for ensuring that the correct base is inserted. For instance, in *E. coli*, the parental strand is methylated, while the newly synthesized strand is initially unmethylated. The mismatch repair system utilizes this methylation mark to identify and remove the incorrect bases from the unmethylated strand.

Defects in mismatch repair genes are linked to a significant increase in mutation rates and are implicated in the development of various cancers, particularly hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome. The continuous accumulation of unrepaired errors can lead to mutations in genes that regulate cell growth and division, contributing to tumorigenesis. Consequently, the mismatch repair system plays a vital role in genome stability and in preventing cancer.