gen380F11StLect12

gen380F11StLect12 - GENETICS 380 LECTURE 12: DNA Replication

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http://www.cellimagelibrary.org/images/10086 GENETICS 380 LECTURE 12: DNA Replication
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Important Features of DNA Structure - made up of 2 complementary single strands - H-bonding between bases ( base-pairing ) of complementary strands is specific - A with T - G with C Watson & Crick proposed a mechanism suggesting how DNA might be copied
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DNA Replication 1. must be accurate 2. must be fast MISTAKES sequence changes will be passed to all progeny cells may destroy cell viability/function E. coli genome has 4.6 million base pairs divides every 20 minutes
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Three models for mechanism of DNA replication 2. semi-conservative 1. conservative 3. dispersive 2 strands original 2 strands new 1 strand original ; 1 strand new 1 strand original ; 1 strand new 2 strands m i x e d 2 strands m i x e d Fig 12.1; p317
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Two experiments proved semi-conservative model 2. Taylor experiment (in eukaryotes) 1. Meselson-Stahl experiment (in prokaryotes) - studied E. coli 1 circular chromosome Meselson-Stahl - used heavy isotope of Nitrogen ( 15 N) to label DNA - “normal” Nitrogen is 14 N Let = 14 N-containing DNA (light) = 15 N-containing DNA (heavy) E. coli grown many generations in 15 N double stranded DNA (ds DNA)
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Density Gradient Centrifugation DNA is extracted from cells,
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gen380F11StLect12 - GENETICS 380 LECTURE 12: DNA Replication

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