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The rate of DNA repair depends on various factors, including the cell type, the age of the cell, and the extracellular environment. A cell that has accumulated a large amount of DNA damage or can no longer effectively repair its DNA may enter one of three possible states: an irreversible state of dormancy, known as senescence
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.
Decreased rates of homologous recombination cause inefficient DNA repair, [107]: 310 which can also lead to cancer. [108] This is the case with BRCA1 and BRCA2, two similar tumor suppressor genes whose malfunctioning has been linked with considerably increased risk for breast and ovarian cancer.
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.
Experimentally, mutation rates increase substantially in cells defective in DNA mismatch repair [20] [21] or in Homologous recombinational repair (HRR). [22] In both prokaryotes and eukaryotes, DNA genomes are vulnerable to attack by reactive chemicals naturally produced in the intracellular environment and by agents from external sources.
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Of these, 83 are directly employed in the 5 types of DNA repair processes indicated in the chart shown in the article DNA repair. Mammalian nuclear DNA may sustain more than 60,000 damage episodes per cell per day, as listed with references in DNA damage (naturally occurring). If left uncorrected, these adducts, after misreplication past the ...