Biology 2581B Study Guide - Quiz Guide: Pyrimidine Dimer, Hypoxanthine, Depurination
2 May 2020
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Deamination: results in spontaneous loss of an amine group. E. g. converts a cytosine base to a uracil. Without dna repair, spontaneous dna damage would rapidly change dna sequences. Endogenous e. g. reactive metabolites (ros, h2o), replication errors. Exogenous e. g. uv radiation, x-rays, mutagenetic chemicals. Mutation hotspots: where the same amino acid position is mutated in many tumors, e. g. deamination of 5-methyl cytosine thymine. These causes distortion in helix which prevents replication and transcription. Pyrimidine dimers are molecular lesions formed from thymine or cytosine bases in dna via photochemical reactions. Ultraviolet light (uv) induces the formation of covalent linkages between consecutive bases. Base excision repair: repairs damage dna throughout the cell cycle. It is responsible primarily for removing small, non-helix-distorting base lesions from the genome. Nucleotide excision repair: damaged bases are cut out within a string of nucleotides and replaced with. Dna as directed by the undamaged template strand. This repair system is used to remove pyrimidine dimers formed by uv radiation.
