Brooker_Chp11P - Chapter 11 DNA Replication Possible models...

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Unformatted text preview: Chapter 11 DNA Replication Possible models for DNA replication Meselsons & Stahls Experiment Escherichia coli cells grown for many generations in culture medium containing only 15 N. Collect E. coli by gentle centrifugation, wash, resuspend in growth medium containing only 14 N. At various times, collect cells and analyze chromosomal DNA. Equilibrium density gradient centrifugation Meselson & Stahl (continued) Generation 1 result disproves conservative model Generation 2 (1.9) supports semiconservative model Meselson and Stahl- disproved conservative and dispersive DNA replication, leaving semiconservative replication as the best answer. Bacterial systems, specifically E. coli , served as the model for molecularly describing DNA replication. oriC starting point ter stopping point Search for the enzyme that makes DNA Arthur Kornberg - used Escherichia coli , prokaryote- Isolated DNA polymerase I- Awarded Nobel prize in medicine Researchers identified & grew E. coli mutants that lacked DNA polymerase I [ pol I- ]- Oops!! Led to discovery of other DNA polymerases DNA polymerase I, II, III, IV and V in E. coli Characteristics of E. coli DNA polymerases Enzyme Polymerizes 5->3 Exonuclease 3->5 Exonuclease 5->3 ~no./cell Pol I Yes, needs primer Yes Yes 400 Pol III Yes, needs primer Yes No < 20 DNA Polymerase III...
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Brooker_Chp11P - Chapter 11 DNA Replication Possible models...

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