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RKarp-13noarticles - Chapter 13 DNA Replication and Repair...

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Unformatted text preview: Chapter 13 DNA Replication and Repair Fig. 13.1 The original Watson-Crick proposal for the replication of a double-helical molecule of DNA. Semi-conservative replication During replication, the double helix unwinds, and each of the parental strands serves as a template for the synthesis of a new complementary strand . Replication in Bacterial Cells DNA Replication Replication forks and bidirectional replication http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0 Fig. 13.5 Model of a circular chromosome Undergoing bidirectional, semiconservative replication Two replication forks move in opposite directions from a single origin. When the replication forks meet at the opposite point on the circle, replication is terminated and the two replicated duplexes detach from one another. New DNA strands are shown in red. Unwinding the duplex and separating the strands- Unwinding the strands for replication would cause torsional stress that would cause the unseparated portion to become more and more tightly wound. Fig. 13.6 The effect of unwinding a two-stranded rope that has one end attached to a hook To overcome this problem both pro- and eukaryotic cells contain DNA gyrase a toposiomerase that breaks and rejoins the tightly coiled strand ahead of the replication and thereby relieves the tension. DNA replication http://www.sciencemedia.com/website/demos/biochem/ecoliReplication.html The properties of DNA polymerase. DNA polymerase requires a single stranded template and a primer, i.e., the deoxynucleotides can only be added to a 3' OH terminus and cannot initiate the synthesis of DNA. Bad Good a) the polymerization of a nucleotide onto the 3 end of the primer strand c) schematic of movement of DNA polymerase along the two template strands. Fig. 13.8 The incorporation of nucleotides onto the 3 end of a growing strand by a DNA polymerase. b) Mg-dependent exchange Fig. 13.9 The two strands of double helix are synthesized by a different sequence of events. a) schematic diagram depicting the differences in synthesis of the two strands. The short strands of the lagging strand are called Okazaki fragments. b) electron micrograph of a replicating bacteriophage DNA molecule . Fig. 13.10 Results of an experiment showing that part of the DNA is synthesized as small fragments....
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RKarp-13noarticles - Chapter 13 DNA Replication and Repair...

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