Lecture4_DNA Replication

Lecture4_DNA Replication - Semiconservative Challenges...

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Semiconservative • Mechanism details • Elements required for chromosome Central Dogma of Biology and information flow
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Meselson-Stahl Experiment http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.html http://www.dnaftb.org/dnaftb/20/concept/index.html
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How is DNA copied? Conservative mechanism Semiconservative mechanism Two possible ways: Initial DNA duplex is conserved No conservation of initial DNA duplex
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Results of Meselson-Stahl experiment
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DNA H H H H Incoming dNTP T T pyrophosphate (PPi) • 5’ to 3’ strand growth of DNA • DNA pol. moves down template DNA from 3’ to 5’ (see big yellow arrow at left) • opposite 5’ to 3’ directionality (recall that dsDNA is “antiparallel”) phosphodiester bond - formation catalyzed by DNA Polymerase DNA synthesis is very accurate. When mistakes in incorporation occur they can be corrected by proofreading steps.
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1. Origin recognition complex (ORC) binding (hexameric complex) at replication origin 2. Unwind DNA at origin of replication 3. Primase synthesizes RNA primer 4. Additional unwinding 5. Leading-strand extension 6. Synthesis of lagging-strand primer 5. Leading-strand extension (cont.) 7. Extension of lagging-strand 8. Ligation of Okazaki fragment
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Helicase binds and unwinds and separates DNA strands (requires energy) Topoisomerase I relieves torsional stress (supercoils) on duplex DNA that results from helicase activity Step 3: DNA polymerase requires RNA primer for initiating DNA synthesis DNA polymerase extends from primer Figure16-15. Biology, 7th edition Primase synthesizes RNA primer DNA polymerase will extend from 3’ end of primer. DNA synthesis occurs 5’ to 3’
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This note was uploaded on 01/20/2010 for the course BIMM 100 taught by Professor Pasquinelli during the Spring '06 term at UCSD.

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Lecture4_DNA Replication - Semiconservative Challenges...

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