LECTURE 3-DNA polymerases-poor enzymes doing half the job

LECTURE 3-DNA polymerases-poor enzymes doing half the job -...

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1. DNA replication is semi-conservative. 2. DNA polymerase enzymes are specialized for different functions. 3. DNA pol I has 3 activities: polymerase, 3’-->5’ exonuclease & 5’-->3’ exonuclease. 4. DNA polymerase structures are conserved. 1. But: Pol can’t start and only synthesizes DNA 5’-->3’! 1. Editing (proofreading) by 3’-->5’ exo reduces errors. 2. High fidelity is due to the race between addition and editing. 3. Mismatches disfavor addition by DNA pol I at 5 successive positions. The error rate is ~ 1/10 9 . DNA polymerase Summary
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DNA replication is semi-conservative Meselson-Stahl experiment 1. Grow E. coli on 15 N (“heavy”) ammonia 2. Switch to 14 N (normal, “light”) ammonia 3. Harvest aliquots as a function of time 4. I solate DNA 5. Separate on the basis of DNA density using density gradient centrifugation 2
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Predictions of Meselson-Stahl experiment Conservative Semi-conservative Distributive 0 1 2 Parental strands stay together -- HH maintained Parental strands separate every generation -- no HH after 1 generation Parental strands broken -- no LL in generation 2
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Results of Meselson-Stahl experiment Conservative Semi-conservative Distributive 0 1 2 Parental strands stay together -- HH maintained Parental strands separate every generation -- no HH after 1 generation Parental strands broken -- no LL in generation 2 Results Graph Picture
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Conservative Semi-conservative Distributive 0 1 2 Parental strands stay together -- HH maintained Parental strands separate every generation -- no HH after 1 generation Parental strands broken -- no LL in generation 2 Results Graph Picture DNA replication is semi-conservative
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Arthur Kornberg discovered DNA dependent DNA polymerase
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This note was uploaded on 01/12/2010 for the course MCB 110 taught by Professor Alber,zhou,nogales during the Fall '07 term at University of California, Berkeley.

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LECTURE 3-DNA polymerases-poor enzymes doing half the job -...

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