LS7DNAreplication

LS7DNAreplication - Lecture 7: DNA Replication 1....

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1 Lecture 7: DNA Replication 1. Semi-conservative replication how to test Watson-Crick hypothesis? Meselson-Stahl experiment (1958) 2. Replication process Replication origin and supercoil problem Replication fork and bi-directional replication Leading strand vs lagging strand 3. DNA replication enzymes Helicase, DNA topoisomerase, Primase DNA polymerase, RNase H, DNA Ligase 4. Proof reading of DNA replication 5. How to replicate the end of a linear DNA The Eukaryotic Cell Cycle
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2 Watson-Crick semiconservative hypothesis Based on their model of DNA structure, Watson and Crick hypothesized that DNA replication was semi- conservative -- that means one of each parental DNA strands will be present in each of the two newly synthesized daughter dsDNA Conservative : Both parental DNA strands are conserved in the daughter DNA Semi-conservative: Only one of the two parental strands is conserved in the daughter dsDNA parent daughter Difference between conservative and semiconservative DNA replication Meselson-Stahl experiment (1958) proved the semiconservative DNA replication (page 454, MCB 4th ed.)
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3 1. DNA replication starts from replication origin 2. DNA replication is a DNA template-dependent polymerization process that needs RNA primers 3. DNA synthesis is always from 5’to 3’, so replication of a dsDNA has to proceed in opposite directions (bidirectional replication) 4. DNA is synthesized continuously (leading strand ), as well as discontinuously ( lagging strand is synthesized as Okazaki fragments) 6. DNA replication is very accurate and fast Features of DNA Replication 3’ end hydroxyl group of the existing DNA is where the incoming nucleotide will be added to Direction of DNA Synthesis 5’ to 3’
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4 can be viewed as the extension of existing DNA (or RNA primer) through base pairing with nucleotides on the template. Substrates: Deoxyribonucleoside triphosphates Chemistry: 3’OH attacks phosphate on incoming nucleoside triphosphate DNA synthesis Origin of replication Replication origin is specific places in the genome that the dsDNA is first opened for replication Procaryote —single origin per genome (or plasmid), also called replicon Eucaryote —multiple origins in each chromosome (~10,000 in the human genome) In a large genomic DNA, where will the replication begin?
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LS7DNAreplication - Lecture 7: DNA Replication 1....

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