MBB 222 Lecture Notes - Lecture 7: Dna Repair, Pyrimidine Dimer, Dna Mismatch Repair
4 Dec 2016
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Cytosine deamination: cytosine can deaminate (remove an amine group) spontaneously to form uracil, results in a c-g to t-a transition (c-g u-g u-a t-a, deaminated bases are repaired by base excision repair. Ap (apurinic/apyrimidinic)/ abasic site: base removal leaves an abasic site. Also known as ap site (for apurinic or apyrimidinic: ap endonuclease cleaves the phosphodiester bond near the ap site. Near-uv vs. ionizing radiation: ionizing radiation (x-rays, gamma rays) can cause ring openings, fragmentation of bases, and breaks in the sugar-phosphate backbone of dna (strand breaks) Alkylation: alkyl agents add a methyl or ethyl group (alkylation, generates a spectrum of methylated products. O6-methyl guanine (or mg: a dna repair enzyme that directly repairs the modification/damage before a mutation occurs, also called o6-alkyl guanine (mg) is highly mutagenic, base-pairs with t instead of c (gc at mutation) Oxidative damage: an important source of dna damage by excited oxygen species, hydroxyl radicals are responsible for most oxidative damage.
