LIFESCI 3 Lecture Notes - Lecture 13: Homologous Recombination, Nucleobase, Cytosine
Document Summary
Lecture 13: mmr for lesion missed by polymerase (intrinsic lesions) Endonuclease makes 1 nick in the backbone. Helicase helps separate strands: ner for bulky lesions (extrinsic lesions) Base excision repair (ber) for both intrinsic & extrinsic: removal of chemically modified bases, e. g. C deaminated to u: extrinsic: base oxidation, scans the minor groove & looks fo(cid:396) si(cid:374)gle (cid:374)u(cid:272)leotide that do(cid:374)"t (cid:271)elo(cid:374)g i(cid:374) dna (can be. Intrinsic: spontaneous base hydrolysis intrinsic or extrinsic: uses glycosylase enzyme; cuts beta-glycosidic linkage connecting nitrogenous base to sugar -> removes base first e. g. uracil dna glycosylase. Glycosylase facilitate base flipping in the minor groove. Base flipping rotates a base to the outside of the double helix, so that it can access the base and excise it from the nucleotide during ber. Double strand break repair: generated by both extrinsic & intrinsic sources. X rays or oxygen, free radicals: can break dna in half, 2 ways to repair.
