fall 09 lecture 11

fall 09 lecture 11 - Tuesday, October 13, 6:00-8:00 p.m.,...

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Tuesday, October 13, 6:00-8:00 p.m., TC 2218 Learn more about the medical school application process in Ontario Topics will include undergraduate course selection; tactics for improving the online application; advice on reference letters, personal statements, and interviews. The presenter, Kevin Mayer, will also discuss life as a medical student, the stages of medical training, and help you assess whether a career in medicine is right for you. Sign up at careerservices.uwaterloo.ca , click on “Workshops/Events Calendar” to register.
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DNA Pol I RNase H Removes most of RNA primers’ nucleotides (except the last one, which is directly linked to the DNA) -auxiliary role, mostly if longer primers - Can remove ribonucleotides (including those directly linked to the DNA) - Fills the gap with deoxyribonucleotides ( 5’-3’ “normal” polymerizaton activity ) - Not highly processive (20/100 nt/binding) Both exonuclease activities: - 5’-3’ (removes ribonucleotides) and - 3’-5’ (proofreading)
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IN BOTH CASES: Free 3’ OH necessary for polymerization removes faulty nucleotides fills the gap (as it has a template) DNase I 5’ 3’ removes RNA primer in 5’-3’ removes faulty nucleotide in 3’-5’ 3’
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DNA ligase Enzyme that links fragments on the lagging strand Forms a phosphodiester bond between the 3’-OH terminus and the 5’-PO 4 terminus of adjacent nucleotides
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Topoisomerases Enzymes that recognize and regulate supercoiling Also involved in DNA replication and transcription Two types Topoisomerase I and II Major role in replication Topoisomerase II (gyrase) requires ATP 1. introduces negative supercoils around OriC- necessary for initiation of replication by DnaA 2. After helicase’s action positive supercoils are formed ahead of a growing fork; Topoisomerase II converts them into negative .
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Two DNA Pol III cores are connected by τ dimers Leading strand core elongates leading strand from RNA primer in direction of growing fork Lagging strand core synthesizes Okazaki fragment from RNA primer (loop is formed between lagging core and growing fork) γ complex holds new sliding clamp ( β ) Replication fork: RNA primer Okazaki fragment: RNA-DNA fragment
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Loop is growing; lagging core displaces SSB and finishes Okazaki fragment Primase is positioned by helicase so it could make a new RNA primer (10-15 nt long) for the lagging strand
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New primer is made and primase is released β clamp releases finished Okazaki fragment from the lagging core Lagging core stays connected to the leading core through τ subunit
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γ complex loads new β clamp onto the newly synthesized RNA primer; Lagging core will bind to β clamp (and become processive again) and start polymerization from the RNA primer DNA Pol I removes all rNTPs (RNA primer) and replaces them with dNTPs Ligase ligates all consecutive fragments
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Q: How to remember all enzymes and other factors involved in DNA replication A: We have to think about what has to happen DNA tightly packed enzyme necessary to initiate process by binding to OriC
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This note was uploaded on 07/10/2010 for the course BIOL 308 taught by Professor Miskovic during the Fall '09 term at Waterloo.

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fall 09 lecture 11 - Tuesday, October 13, 6:00-8:00 p.m.,...

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