F08-BCH361-L13

F08-BCH361-L13 - Replication Replication of DNA Naturally...

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Replication
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Replication of DNA • Naturally occurring DNA exists in single- and double-stranded forms, both of which can exist in linear and circular forms • We will first study the replication of circular double-stranded DNA and then of linear double-stranded DNA – most of the details we discuss were first investigated in prokaryotes, particularly E. coli
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Procaryotic cell in process of division
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Flow of Genetic Information •Mechanisms for the transfer of information in the cell
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Replication is semi-conservative
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Prokaryotic Replication • Replication involves separation of the two original strands and synthesis of two new daughter strands with the original ones as templates Semiconservative Semiconservative replication replication : each daughter strand contains one template strand and one newly synthesized strand – was established in the late 1950s by experiments of Meselson and Stahl – a key observation is that 15 N-DNA has a higher density than 14 N-DNA, and the two can be separated by density-gradient ultracentrifugation
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Prokaryotic Replication • The Meselson-Stahl experiment E. coli bacteria were grown for a prolonged time in a medium with 15 NH 4 Cl as the sole source of nitrogen; as a result, cells contained only 15 N-DNA – these cells were then grown in a medium containing only 14 NH 4 Cl – after one generation growth in the 14 NH 4 Cl medium, cellular DNA was 14 N, 15 N-DNA; each DNA molecule contained one heavy strand and one light strand – after two generations growth in the 14 NH 4 Cl medium, one-half of cellular DNA was the 14 N, 15 N-DNA hybrid and one-half was 14 N-DNA
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Experiment which shows that replication is semi- conservative
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Prokaryotic Replication • Challenges in duplication of circular double- stranded DNA – how to achieve continuous unwinding of the two DNA strands – how to protect the unwound portion from attack by nucleases that attack single-stranded DNA – the DNA template has one 5’ -> 3’ strand and one 3’ -> 5’ strand; how to synthesize daughter DNA in the 5’ to 3’ direction from each parent strand – how to guard against errors in replication
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Prokaryotic Replication – DNA double helix unwinds at a specific point called an origin of replication origin of replication – at each origin of replication, there are two replication replication forks forks
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This note was uploaded on 09/30/2011 for the course BCH 361 taught by Professor Fromme during the Fall '08 term at ASU.

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F08-BCH361-L13 - Replication Replication of DNA Naturally...

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