S1.Describe three ways to account for the high fidelity of DNA replication. Discuss the quantitative contributions of each of the three ways. Answer: First: AT and GC pairs are preferred in the double helix structure. This provides fidelity to around one mistake per 1,000. Second: Induced fit by DNA polymerase prevents covalent bond formation unless the proper nucleotides are in place. This increases fidelity another 100- to 1,000-fold, to about one error in 100,000 to 1 million. Third: Exonuclease proofreading increases fidelity another 100- to 1,000-fold, to about one error per 100 million nucleotides added. S2. What do you think would happen if the ter sequences were deleted from the bacterial DNA? Answer: Instead of meeting at the ter sequences, the two replication forks would meet somewhere else. This would depend on how fast they were moving. For example, if the counterclockwise-moving fork was advancing faster than the clockwise-moving fork, they would meet closer to where the clockwise-moving fork started. In fact, researchers
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This note was uploaded on 04/07/2009 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.