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Unformatted text preview: Biochem Chapter 24 Outline DNA Replication, Repair, and Recombination 1) DNA Replication a) Semiconservative when replication results in two molecules of duplex DNA< each consisting of one polynucleotide strand from the part, and one brand new one b) Conservative- parental DNA would remain intact, and both strands of daughter would be new c) DNA is replicated by enzymes (called DNA-directed DNA polymerases, or just DNA polymerases) i) Uses DNA as templates. Reaction occurs through nucleophilic attack of growing DNA chains 3 OH on the alpha-phosphoryl of an incoming nucleoside triphosphate ii) Nearly all known DNA polymerases can add nucleotides only to the free 3 OH, so DNA chains are extended only in the 5-3 direction d) Replication occurs at replication forks i) Replication eyes or bubbles known as theta structures form when two parental strands separate to allow synthesis. DNA replication involving this is known as theta replication ii) Branch point in this replication eye known as replication fork. A bubble can contain one or two of these forks (unidirectional or bidirectional replication). (1) Its usually bidirectional e) Replication is semidiscontinuous i) Duplex DNAs two antiparallel strands are simultaneously replicated at the forks. ii) How is the parent strand that extends in the 5-3 direction be copied, if polymerases only create in the 5-3 direction? (1) Okazaki fragments (2) Semidiscontinuous replication two parent strands are replicated in different ways (a) Leading strand continuously synthesized in its 5-3 direction...
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This note was uploaded on 07/08/2008 for the course PSB 332 taught by Professor Gracz during the Spring '08 term at MCPHS.
- Spring '08