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BIOL 205 (111)


6 Pages

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BIOL 205
Ian D Chin- Sang

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BIOL205:week 8, lecture 21 DNAsynthesis is fast and accurate! • 2000 nucleotides/second- in E. coli two forks moving at 1000 nucleotides/second • E.coli genome 5 million base pairs- 40 minutes • signals in E. coli nearly identical to humans (highly conserved) • 1 nucleotide error in 10 inserted (thanks to 3’-5’exonuclease proofreading (Pol I and III)) Initiation of Replication • the origin of replication in E. coli is termed oriC ◦ origin of Chromosomal replication • three types of DNAsequences in oriC are functionally significant ◦ AT-rich region (easier to open up due to fewer H-bonds, Vanderwaals forces) ◦ DnaAboxes: sequences recognized by DAprotein ◦ GATC methylation sites • many proteins are required Unwinding the double helix • two enzymes open helix and prevent overwinding: helicase and topoisomerase (=DNAgyrase ◦ helicase: clamps to DNA–breaks hydrogen bonds ahead of DNAsynthesis ◦ SSB: single strand DNA binding proteins –bind to unwound DNA and prevent it from re- forming ▪ whenever single stranded DNA, always have SSB proteins jumping on as soon as possible b/c at this point DNAis most vulnerable • DNaAbinding proteins stimulte other proteins and open up origin of replication Prokaryotic initiation of replication replisome:containDNApolymerases Topoisomerase/ DNAgyrase removes extra twists Unwidingstrand:causes bucklingfurther downDNAstrand DNAgyrase removes extra twists –relaxes DNA
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