Biochemistry - Outline ch.24

Biochemistry - Outline ch.24 - Biochem Chapter 24 Outline...

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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 chain’s 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) It’s usually bidirectional e) Replication is semidiscontinuous i) Duplex DNA’s 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 
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