10:9 Proteins and Nucleic Acids

5 c 5 5 a 3 5 h 3 c o 5 t dna polymerase a 5 a 3 5 g

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Unformatted text preview: 5' 3' O 5' DNA polymerase A G G O T A G T 3' A original (double-sided) DNA molecule O activated deoxyribonucleotides two indentical copies of the original (double-sided) 5' 3' DNA molecule 5' 3' 5' 3' two (double-sided) DNA molecules identical (same sequence) to the original molecule H 3' O 5' 3' 3' 5' H original (double-sided) DNA molecule x Zero x Zero Vma Some details: Some details: Some details: Vma two identical (same sequence) DNA molecules, other stuff (DNA replication proteins, original DNA molecule) 3 phosphates two identical (same sequence) DNA molecules, other stuff (DNA replication proteins, original DNA molecule) G base pair: G-C, A-T 11-2 Complication of growing 5’ to 3’: (a) easy to envision, but wrong (b) more complicated, but correct d growth direction Problem: the newly forming DNA molecule is growing in the 3' to 5' direction. growth direction lea di n tem g st pla ran te d lea din tem g st pla ran te d growth direction nd tra g s te gi n pl a lag tem starting point growth direction n tr a g s te gin pla lag tem starting point starting point Okazaki fragments fused together by the action of an enzyme called DNA ligase new Okazaki fragment DNA care-taking: 1. DNA polymerase proofreading: 5' 3' C ved A T A C C G A remo T A T G G C T A T A 5' G Once a matching end is restored, DNA polymerase resumes activity. A 5' 3' T A C C G T A T G G C T A T A T A 5' G Most likely, the second time around a mismatch will not occur. AAT 5' 3' T A ACC T GG C G G C T A A A T C C T A G T A T 5' 2. Why 5’ to 3’? T 3' 5' C T A G A T T A G C A T C G G 3' Mistake is made during DNA formation along a template forming a mismatch along terminal end of newly forming DNA. 3' 5' C T A T A G C T G A T A T C G G T A T 3' Due to mismatch, DNA polymerase stops and exonuclease activity clips off the mismatch. 3' 5' T ved C T A T A G C remo G A T A T C G G T A T 3' However, once a matching end is restored, DNA polymerase CANNOT resume activity because an activating triphosphate is no longer available to power the reaction. FurtherDNAsynthesisisthusterminated. an activated triphosphate here is not in the right place to power the reaction. C 3' 5'...
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This document was uploaded on 03/27/2014.

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