Lec6 - Lecture 6 DNA Replication 1 (Lodish 6th Ed. Chapter...

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Lecture 6 DNA Replication 1 (Lodish 6th Ed. Chapter 4.5) (Lodish 5th Ed. Chapters 4.6 and 23.5)
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The Meselson-Stahl Experiment: DNA Replication is Semiconservative Theoretical Experimental
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Replication begins at Origins and Proceeds Bi-directionally Replication of a bacterial or some viral chromosomes
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In Eucaryotic Chromosomes multiple replication origins are used to more rapidly replicate the DNA in S phase Yeast Replication Fork Replication Forks
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“Primer” required (3’OH) Synthesis: 5’ to 3’ direction (Adds to 3’OH of primer) PROPERTIES OF THE DNA POLYMERASES
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DNA Synthetic Reaction Mechanism: Elongation Nucleophilic Attack Rate : • Bacteria ~1,000 bp/sec (43 min to replicate genome) • Eucaryotes ~100 bp/sec (8-10 hrs to replicate) •Spinning of Replication Fork in Bacteria: 1000 bp/sec 10.4 bp/turn of helix =6,000 rpm • 1 origin (2 forks) in most bacteria • Mammals: 100 bp/sec ~10,000-1000 origins/3x10 9 bp in human (10 hrs to replicate)
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Nucleotide analogues are used to treat disease • Zidovudine [ZDV; (AZT)] an analogue of deoxythymidine • Used to treat AIDS • Does not allow further DNA chain elongation (no 3’OH)
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ddI is also used to treat HIV infection • ddI is a reverse transcriptase inhibitor. Its method of action is the same as AZT. • Dideoxyinosine enters the GMP/dGMP biosynthetic pathway leading to dd TTP . Inosine 2’-3’-Dideoxyinosine
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Enol tautomer can pair with the “wrong” base N O O CH 3 deoxy- ribose deoxy- ribose O N H H H H G with enol-T N H H H O CH 3 deoxy- ribose deoxy- ribose A-T base pair T-keto T-enol Note: Tautomers are two forms of the same compound which differ by positions of a hydrogen atom and a pi bond (I.e. location of a double-bond). Ketones and enols are tautomers. The form which exists in highest concentration is determined by their relative stability. In most cases (and in the case of T, the keto form is the more stable tautomer.
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Proof Reading by DNA Polymerases DNA Polymerases a a. 5’ to 3’ polymerization b. 3’ to 5’ exonuclease
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Lec6 - Lecture 6 DNA Replication 1 (Lodish 6th Ed. Chapter...

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