User:IshDatta/sandbox

DNA repair

Mitochondrial DNA Repair
Mitochondria is a double membrane bound organelle present in eukaryotic cells in large numbers; it contains a small, circular, double stranded DNA molecule that is inherited by maternal inheritance. The biochemical process of respiration takes place in mitochondria and this results in continuous production of cellular energy along with generation of Reactive Oxygen Species(ROS) that damages the mitochondrial DNA. Unlike Nuclear DNA which has several mechanisms for resolving chromosomal DNA damage mitochondria is unable correct all possible forms of DNA damage, also coupled with the proximity of mt DNA to ROS and the lack of protective histones increases the susceptibility of mt DNA to DNA damage. If the DNA damage in mitochondria persists it hinders the activity of mitochondrial DNA polymerase and RNA polymerase (POLRMT) and also threatens mtDNA and gene expression. Almost all known nuclear DNA repair pathways exist in mitochondria. This includes Base Exicision Repair mechanisms like SN-BER and LP-BER, Single Strand Break Repair (SSBR),DNA mismatch repair. Mitochondria also has double stranded break repair systems including Homologous Recombination Repair and Non-homologous end joining repair(NHEJ).However, mitochondria lacks Nucleotide excision repair activity(NER) that is mitochondria is unable to rectify bulky DNA damage for example UV photoproducts, oxidative lesions, cisplatin cross links. A specific mitochondrial repair mechanism in response to Oxidative Species(OS) is the degradation of unrepairable mt DNA unlike nuclear DNA. The proteins involved in mitochondria DNA repair are however not encoded by mt DNA, they are actually encoded by nuclear genes and have to be transported in to the mitochondria for their function. [NOTE FROM HWB: this paragraph needs additional editing, but will become a nice addition]