BIOL 222 Lecture 32: DNA Repair
3 Dec 2016
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Photo-reactivation: photolyase, thymine dimers, problem: when dna is exposed to uv radiation, thymine dimers are formed covalent bonds between thiamines. Helix structure is also distorted: solution: uv can also activate the photolyase gene, which then is activated to be transcribed, making photolyase enzyme. This enzyme recognizes chromosome distortion and uses light energy to remove the covalent bond between the two t"s: photolyase - not present in some mammals (humans don"t have it) Photolyases vs. cryptochromes: cryptochromes are similar to structure to photolyases. Can sense blue light, in the visible spectrum. But they do not function in dna repair, are for regulating the circadian rhythm. Nucleotide excision repair (ner: uvr proteins, typically recognizes bases that distort the dna helix, can be used to repair uv-induced thymine dimers in placental mammals. Called the dark repair pathway for repairing thymine dimers: this is because it doesn"t require light, unlike photolyase, steps: 1. identifying the mutation: uvra (x2) and uvrb.
