Answer4 - MCB 161 Lecture 4: DNA Replication (I) MBOC...

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MCB 161 Study Problems Lecture 4: DNA Replication (I) MBOC Problems book: 5-20 False. The sequence of nucleotides in a newly synthesized strand is very different from that of the parental strand used as the template for its synthesis; the new strand is complementary to the 3’-to-5’ sequence of the parental template strand. 5-39 A. A replication ‘bubble’ with two replication forks moving in opposite directions is shown in Figure 5–50. Arrowheads show the 3’ ends of the growing chains. B. The four structures that were most commonly observed, along with those that were never seen, are indicated in Figure 5–51. Based on the mechanism of bidirectional DNA replication, you might well have picked structure 5 as the most common because it has two single-stranded regions corresponding to the expected sites of lagging-strand synthesis. Structure 8 is also a reasonable expectation; it appears that lagging strand synthesis at one end has not yet filled in the single-strand gap. It is somewhat unexpected that structures like 1 and 3, which have no single-stranded DNA at one or both forks, were observed so commonly. These structures could result from asynchronous growth at the fork (such that the leading strand pauses until the lagging strand catches up), from some artifact of the preparation of DNA for viewing, or from single-stranded regions that were too short to be distinguished reliably from double-stranded DNA. Reference: Inman RB & Schnos M (1971) Structure of branch points in replicating DNA: presence of single-stranded connections in lambda DNA branch points. J.Mol. Biol. 56, 319–325.
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5-41 A. The different labels used for the T and C nucleotides make it easy to measure their respective losses from the polymeric substrate. The radioactive disintegrations from the energetic 32P and from the rather weak 3H can be distinguished using a liquid scintillation counter. B. Because DNA polymerase I possesses an exonuclease activity (that is, it removes nucleotides from the ends of strands), the T nucleotides cannot be released until all the C nucleotides have been removed; hence the lag. C. When dTTP is added to the reaction, polymerization will begin just as soon as a proper
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This note was uploaded on 01/24/2010 for the course BIS 104 taught by Professor Scholey during the Winter '08 term at UC Davis.

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Answer4 - MCB 161 Lecture 4: DNA Replication (I) MBOC...

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