30_Lieb_DNA_Repair - Biology 202-Lieb DNA Repair I Cellular...

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Biology 202-Lieb DNA Repair Page 1 of 2 I. Cellular responses to DNA damage In addition to repair or reversal of damage (II and III below), other mechanisms exist: bypass – DNA polymerase is blocked by many types of damage; special bypass polymerases can synthesize past apurinic sites or pyrimidine dimers. However, these are typically very error-prone (they just make a “best guess” as to what nucleotides to incorporate). cell cycle arrest – replication or mitosis in the presence of damage can be disastrous; most cells will arrest progression through S phase or entry into M phase until damage is repaired. apoptosis – in metazoans, cells experiencing too much damage can kill themselves II. Overview of some DNA repair strategies DNA repair mechanisms are named according to when they occur ( e.g. , postreplication repair), what type of damage they act on ( e.g. double-strand break repair), or actual mechanism ( e.g. nucleotide excision repair). A. When damage is limited to one strand , repair pathways use the complementary strand: Base excision repair (BER) corrects damaged and missing bases 1) DNA glycosylase removes a single base by cleaving the nucleoside linkage (also called glycosidic bond); leaves an apurinic or apyrimidinic (AP) site; specialized glycosylases recognize bases damaged by reactive oxygen species, uracil, etc.
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  • Fall '07
  • MITCHELL
  • Genetics, DNA, DNA repair, DNA Damage, Nucleotide excision repair, double-strand break repair

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