Lecture #21 - BioMI 290 Fall 2007 Lecture 21 Lecture 21 DNA...

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BioMI 290, Fall 2007, Lecture 21 1 Lecture 21 DNA Replication (DNA S th i ) (DNA Synthesis) BBOM 11e Sec. 7.5-7.6 Escherichia coli Watson and Crick: “It has not escaped our notice that the specific pairing we have postulated immediately suggests a plausible copying Semiconservative ds DNA mechanism 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 21 2 1957 Meselson & Stahl 1. Labeled original DNA with heavy 15 N . 2. Cells grown in 14 N . 3. DNA extracted & nt if d in CsCl ft 1 1 generation Many generations 15 15 15 15 14 14 centrifuged in CsCl after 1 round or more of replication. Semi- conservative Conservative Semi- conservative Conservative 15 N 15 N 15 N 15 N 14 N 14 N 15 N 15 N 15 N 14 N 14 N 15 N Conservative Semi-conservative 14 N 15 N 14 N 15 N + 14 N 15 N 14 N 15 N + 14 N Generations after change from 15N to 14N 0 0.3 0.7 1.1 1.0 1.5 1.9 2.5 3.0 4.0
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