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lec18 - Biochemistry I Fall Term 2004 October 13 15 2004...

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1 Biochemistry I Fall Term, 2004 October 13 & 15, 2004 Lecture 18: DNA Replication & Repair Assigned reading in Campbell: Chapter 9.1-9.6 Key Terms: Leading and lagging strand synthesis Exonucleolytic editing E. coli Pol I & Pol III holoenzyme Nick translation DNA gyrase, DNA ligase, primase, & helicase Eukaryotic Pol α & Pol δ Reverse transcriptase Pyrimidine dimers Nucleotide excision repair Processive polymerization Links : ( I ) Review Quiz on Lecture 18 concepts ( I ) DNA Replication Tutorial Flash animation of prokaryotic replication. ( I ) Enzymes & Proteins that act on DNA Handout is a worksheet to accompany this lecture. 1. DNA Replication: an overview. Much of the complexity found in DNA replication (compared, say to transcription) derives from the requirements in all organisms for: high accuracy in duplicating the primary genetic information; high speed and processivity, so as to complete a copy of the genome in less than one cell generation (cell division time). Accuracy and speed cannot both be maximized; instead, each organism has evolved mechanisms to optimize these twin requirements. Moreover, it turns out that most of these mechanisms share a common set of basic principles. Thus, the enzymes involved, the accessory proteins required, and the DNA structures they work on have been conserved in evolution from viruses, to bacteria, to yeast, to fruit flys, to humans. A. Replication Forks 1. DNA polymerases can add nucleotides only to a pre-existing chain. 2. All DNA (and RNA) polymerases synthesize chains from 5' --> 3'. 3. DNA synthesis occurs at replication forks .
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2 a) Synthesis is bidirectional from a replication origin (or origins). b) Replication forks are highly organized structures in cells (DNA synthesis "machines").
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