AT Lecture 12

AT Lecture 12 - BISC 330L: Biochemistry Spring Semester...

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BISC 330L: Biochemistry Spring Semester 2012 USC Lecture 12: Monday, 06 February 2012 1. Chapter 4: Flow of Genetic Information DNA Replication Transcription
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Three functions of DNA as the genetic material: 1. Storage of genetic material 2. Contains the information that directs its own duplication 3. Must contain the information that directs the assembly of proteins DNA RNA PROTEIN PROTEIN
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Fig. 4.16 Diagram of semi-conservative DNA replication.
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Density-Gradient Centrifugation: In terms of density, RNA > DNA > Protein > Lipid . A concentrated CsCl solution (density 1.7 gm/ml), containing cell extract, upon utlra-centrifugation (100,000 x g), creates a density gradient (1.6-1.8 gm/ml) that gives very good separation of RNA and DNA from each other and from Lipids & Proteins. Lipids & Proteins float on top of the CsCl solution, while RNA and DNA form distinct bands in the solution, at the Levels equal to their densities.
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ig. 4.14 Resolution of 14 N DNA and N DNA in CsCl density gradient Ultracentrifugation). To obtain 15 N DNA Meselson and Stahl grew E. coli for several generations in medium containing 15 NH 4 Cl as sole nitrogen source. Then they introduced 14 NH 4 Cl as nitrogen source. DNA DNA heavy light
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Detection of semiconservative DNA replication in E. coli , by Stahl, 1958.
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Importance of 14 N/ 15 N and Centrifugation * * *
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DNA Replication Basics Catalyzed by DNA polymerases (there are three DNA pol I, II, and III) none of these alone can initiate DNA chains, in either direction Direction of synthesis is 5’ 3’ Initiation requires a “primer” with a free 3’OH 3’OH attacks phosphate on incoming nucleoside triphosphate Both strands of DNA are duplicated at the same time DNA polymerase cannot unwind duplex by itself Many accessory proteins are required
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a circular bacterial DNA from one origin Eukaryotic replication
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This note was uploaded on 03/15/2012 for the course BISC 330L taught by Professor Petruska,tower during the Spring '07 term at USC.

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AT Lecture 12 - BISC 330L: Biochemistry Spring Semester...

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