BIOL 200 Lecture Notes - Lecture 17: High Fidelity, Proofreading, Dna Replication
7 Jun 2016
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Document Summary
Based on proofreading : before adding the next nucleotide to the 3"-end of the growing chain, dna polymerase always checks: the just-incorporated nucleotide, if that last nucleotide is mis-paired with the template strand the dna polymerase. Proofreading contributes to the remarkable fidelity of dna synthesis: 1 error in 109, 3 errors in the genome. By contrast, rna polymerase (no proofreading) makes ~1 error in 104. Proofreading mechanism may help explain why dna polymerase requires a primer: dna polymerase cannot start a new chain needs primer. Dna polymerase is so nervous about mis-incorporation that , if it cant proofread, it won"t for anything. It cannot add a nucleotide unless it sees a string od perfectly base-paired nucleotides at a 3"-end: hence necessity of primer. Dna polymerase algorithm: step 1: check previous step, step 2: if correct, add new. Dna replication starts with rna (made by primase)
