Haines-3

Haines-3 - DNA Replication DNA Is Reproduced by...

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DNA Replication
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DNA Is Reproduced by Semiconservative Replication Replication is essential function of the genetic material and must be executed precisely Based on their DNA model, Watson and Crick proposed how replication occurs, termed Semiconservative replication -The complementarity of DNA strands allows each strand to serve as a template for synthesis of the other, leading to a double- stranded DNA molecule consisting of a old and new strand.
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Semiconservative replication not the only possibility, conservative and dispersive models were also proposed After synthesis, new and old strands associate with themselves, hence the original helix is conserved After synthesis, new and old strands intermix
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The Meselson-Stahl experiment (published in 1958) demonstrated that DNA replication is semiconservative Relied on the use of 15 NH 4 Cl as the only nitrogen source. 15 N contains one more neutron and is heavier Will sediment at heavier densities (bottom of tube)
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The data: Disproves the conservative theory, always would have the heavy band and light (at varying ratios, never intermediates) Also consistent with the dispersive replication theory, however this was disproved by denaturing the DNA into single strands and showing that they distributed either a 15N or 14N profile, not a single banding gradient
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The Taylor-Woods-Hughes experiment demonstrated that DNA replication is semiconservative in eukaryotes Use of 3H-thymidine, colchicine (chemical that arrests cells in metaphase) and autoradiography After first round of replication in the presence of isotope-both sister chromatids are labeled (if conservative, one will be labeled and one not) Also, after second round which is done in the absence of label half the sister chromatids are labeled
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Origin of replication: this is the location on the DNA where replication begins Replication fork: site where replication is occurring and DNA is unwound Replicon: the portion/length of
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This note was uploaded on 04/04/2008 for the course BIO 2204 taught by Professor Athwal/haines during the Spring '08 term at Temple.

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Haines-3 - DNA Replication DNA Is Reproduced by...

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