22 Oct 07

22 Oct 07 - Testing Early Hypotheses about DNA Replication...

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Unformatted text preview: Testing Early Hypotheses about DNA Replication • How is DNA copied, so that genetic information can be accurately transferred – from one cell to another during growth (mitosis) – from parents to offspring (meiosis and fertilization)? There were initially three, alternative hypotheses (or models) for DNA synthesis. The results of the Meselson- Stahl experiment supported which of these models? A. dispersive B. semiconservative C. conservative D. None of the above Testing Early Hypotheses about DNA Replication • Three models (hypotheses) of DNA replication were proposed. Semiconservative replication : • Each old DNA strand is copied to generate a new strand. – Each new chromosome is composed of one strand of old DNA and one strand of newly synthesized DNA . The Meselson-Stahl Experiment • To determine which hypothesis was correct, Meselson and Stahl first grew E. coli in the presence of “heavy” nitrogen ( 15 N) and then transferred them into a medium containing “light” or normal ( 14 N) nitrogen. The Meselson-Stahl Experiment • After growing bacteria for many generations in 15 N (“heavy”) medium, they removed a sample of cells --“generation 0”-- and moved the rest to normal, 14 N- containing medium (“light” medium). The Meselson-Stahl Experiment • The generation 0 cells grown in heavy nitrogen ( 15 N) were broken open, and...
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This note was uploaded on 04/07/2008 for the course BIOL 100 taught by Professor Staff during the Fall '07 term at UMBC.

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22 Oct 07 - Testing Early Hypotheses about DNA Replication...

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