Lecture 19 Spring 2011

Lecture 19 Spring 2011 - CsCl centrifugation of DNA over...

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Unformatted text preview: CsCl centrifugation of DNA over time developed by Meselson and Stahl Question 1: (3pts) Why does one add EtBr to CsCl gradients for the isolation of plasmid DNA? In class question (extra credit) for Quiz #4 Question 2: (4pts) Is an 8kb supercoiled plasmid more dense than a 3kb supercoiled plasmid. Yes/No (circle one) Will an 8kb supercoiled plasmid have more EtBr bound to it? Yes/No (circle one) We will talk about this again in a later lecture: But CsCl gradients are not the same thing as Sucrose Gradients or Agarose Gel Electrophoresis . CsCl centrifugation of DNA over time N 15 is heavier than N 14-Can be resolved in CsCl pulse-chase Experiment: Incubator with N 15 containing medium for time, then chase with N 14 medium Expt 1 grows Slowly Expt 2 Bacteria Grow Faster Why? Experiment 1 Experiment 2 N 14 N 15 only Why would they do 2 different growth rates? N 14 N 15 only Fuse Results from Expt 1 and 2 Cell Divisions N 14 N 15 only Experiment 1 observations Watson-Crick Model Does Expt 1 prove hybrid formation? N 14 N 15 only Critical Experiment: Hybrid Strand Separation And CsCl centrifugation N 15 ssDNA N 14 ssDNA N 15 ssDNA N 15 dsDNA Looks like control below What about N 14 / N 15 hybrid? Evolution?Evolution?...
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This note was uploaded on 02/14/2012 for the course BIO 302 taught by Professor Feinstein during the Spring '11 term at Iowa State.

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Lecture 19 Spring 2011 - CsCl centrifugation of DNA over...

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