Biology 1001A Lecture Notes - Lecture 9: Pyrimidine Dimer, Dna Mismatch Repair, Indel
19 Jan 2016
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Why is the wrong tautomeric form of thymine not removed by mismatch. 5-bromouracil is a base-analogue and is incorporated into dna distinguishing by mistake very unstable. ***chemicals are not necessary. tautomeric shifts can happen naturally**: causes mismatch & increases mutation frequency. Mutation > dying: dimers can be repaired by photolyase or excision reverses the consequences of uv and seperates dimers. Mammals do not have any photolyase except for placental mammals: bacteria, plants, archea, animals. In/del mutations long stretch of repetitive dna --> some can loop out while leaving remaining bases stable enough that polymerase does not notice. Template strand slippage: base on the template strand loops out: newly replicated strand has extra base, newly replicated strand has lost a base. Eg in/del mutations genetic anticipation: gets worse with successive generations because more in/del mutations occur eg. huntington"s disease (expansion of number of repeats in.
