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BioMI 290, Fall 2007, Lecture 211Lecture 21DNA Replication(DNA Sthi )(DNA Synthesis)BBOM 11e Sec. 7.5-7.6Escherichia coliWatson and Crick: “It has not escaped our notice that the specific pairing we have postulated immediately suggests a plausible copying Semiconservative ds DNAmechanism for the genetic material.”DNA double helix stores information redundantly, once per strand.Separation of the two strands allows new DNA synthesis to occur on each strand, using the other as a template.
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BioMI 290, Fall 2007, Lecture 2121957 Meselson & Stahl1. Labeled original DNA with heavy 15N.2. Cells grown in 14N.3. DNA extracted & nt ifd in CsCl ft1 1 generationMany generations15 1515 1514 14centrifuged in CsCl after 1 round or more of replication.Semi-conservativeConservativeSemi-conservativeConservative15N15N15N15N14N14N15N15N15N14N14N15NConservative Semi-conservative14N15N14N15N +14N15N14N15N +14NGenerations after change from 15N to 14N00.30.71.11.01.51.92.53.04.0