LEC20 - DNA replication cont Bidirectional Two forks at...

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DNA replication cont.
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Semi-conservative One old strand One new strand Bi- directional Two forks at every origin Discontinuous synthesis On lagging strand. Continuous synthesis On leading strand Ori Ori
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Reiji Okazaki showed that DNA is synthesized as small fragments 1000-2000 bases (prok.) 100-400 bases (euk.) Longer labeling times gives rise to larger fragments but still a peak appears at top of gradient Small Fragmen ts Large Fragments
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Primase is an RNA polymerase that functions only during replication (In E. coli it primes whenever it comes across the 3’ GTC 5’ ) helicase
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How is the RNA removed? 3’->5’ exonuclease activity proofreading function 5’->3’ exonuclease activity remove RNA primers DNA polymerases also possess exonuclease activity
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5’ 5’ 3’ 3’ 3’ 5’ 3’-5’ exonuclease 5’-3’ exonuclease DNA RNA
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Two DNA polymerases involved in replication in E. coli DNA Polymerase III Major replication enzyme Only has 3’ to 5’ exonuclease activity DNA Polymerase I Has both exonuclease activities Removes primers Synthesizes DNA using last Okazaki strand as primer
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Pol III Pol III Pol I ligase
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phosphodiester bond between the new Okazaki fragment and the old one?
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