MCB121 W12 L5 _L6

MCB121 W12 L5 _L6 - I V DNA damage repair and genome...

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IV DNA damage repair and genome instability IV-1. Briefly explain why telomeres do not normally fuse to one another. Discuss protein factors and DNA structures that are involved. IV-2. Explain why genetic information is lost when double-strand breaks are repaired by non- homologous end joining (NEHJ). You can use a diagram if that helps. IV-3 Telomeres are repeated sequences added at the ends of chromosomes to protect the ends from erosion by semi-conservative DNA replication. Telomerase is the enzyme that adds these repeated sequences. From the statement below, circle the appropriate word from the underlined choices given in parentheses: Telomerase is composed of complex including a polymerase and a (DNA / RNA) molecule that serves as the template for the addition of (DNA / RNA) repeated telomere sequences. The process carried out by the polymerase is called (lagging-strand synthesis / reverse transcription). The added telomere sequences end in a free (3’ OH / 5’ phosphate) and extends the template for (lagging/ leading) strand synthesis. If telomere sequences are lost the chromosomal DNA is exposed and is identical in structure to a (DSB / T-loop / thymine dimer).
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IV-4. Shown below is a diagram of how a single break in one strand of the phosphodiester backbone in a DNA double helix can become a double-strand break during DNA replication. Circle “T” or “F” to indicate whether each of the statements below is TRUE or FALSE. T or F In the diagram shown above, the top strand is replicated by lagging-strand synthesis and the bottom strand is replicated by leading-strand synthesis (note: the arrows indicate the 3’ ends of newly synthesized DNA) T or F The DSB generated in the diagram shown above would most likely be repaired using homologous recombination using the newly replicated daughter strand as a template for repair. T or F One strand of the DSB will be resected (chewed back) by an exonuclease moving in the 5’ to 3’ direction to yield single stranded DNA with a free 5 ’ end T or F Replication restart will require a strand invasion event followed by resolution of a single Holliday junction.
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IV-5. Describe one possible fate of a DSB occurring in a cell in G1 phase of the cell cycle. What repair mechanism is likely to be used and possible outcomes.
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This note was uploaded on 03/16/2012 for the course MCB MCB 121 taught by Professor Gasser,burgess during the Winter '11 term at UC Davis.

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MCB121 W12 L5 _L6 - I V DNA damage repair and genome...

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