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Base excision repair (BER) is a cellular mechanism, studied in the fields of biochemistry and genetics, that repairs damaged DNA throughout the cell cycle. It is responsible primarily for removing small, non-helix-distorting base lesions from the genome.
Nucleotide excision repair is a DNA repair mechanism. [2] DNA damage occurs constantly because of chemicals (e.g. intercalating agents ), radiation and other mutagens . Three excision repair pathways exist to repair single stranded DNA damage: Nucleotide excision repair (NER), base excision repair (BER), and DNA mismatch repair (MMR).
Enzymes, namely DNA glycosylases, also commonly create AP sites, as part of the base excision repair pathway. In a given mammalian cell, 5000–10,000 apurinic sites are estimated to form per day. Apyrimidinic sites form at a rate roughly 20 times slower, with estimates at around 500 formation events per day, per cell.
Base excision repair is the mechanism by which damaged bases in DNA are removed and replaced. DNA glycosylases catalyze the first step of this process. They remove the damaged nitrogenous base while leaving the sugar-phosphate backbone intact, creating an apurinic/apyrimidinic site, commonly referred to as an AP site.
Base excision repair (BER): damaged single bases or nucleotides are most commonly repaired by removing the base or the nucleotide involved and then inserting the correct base or nucleotide. In base excision repair, a glycosylase [ 18 ] enzyme removes the damaged base from the DNA by cleaving the bond between the base and the deoxyribose.
Apurinic/apyrimidinic (AP) endonuclease is an enzyme that is involved in the DNA base excision repair pathway (BER). Its main role in the repair of damaged or mismatched nucleotides in DNA is to create a nick in the phosphodiester backbone of the AP site created when DNA glycosylase removes the damaged base.
It is a base excision repair enzyme specific for pyrimidine dimers. It is then able to cut open the AP site. Another type of repair mechanism that is conserved in humans and other non-mammals is translesion synthesis. Typically, the lesion associated with the pyrimidine dimer blocks cellular machinery from synthesizing past the damaged site.
The XRCC1 protein does not have enzymatic activity, but acts as a scaffolding protein that interacts with multiple repair enzymes. The scaffolding allows these repair enzymes to then carry out their enzymatic steps in repairing DNA. XRCC1 is involved in single-strand break repair, base excision repair and nucleotide excision repair. [6]