2000Final_key

2000Final_key - Bio115, Winter 2000 Final Exam Answers...

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Bio115, Winter 2000 Name:_ Answers Final Exam Answers 1 Instructions: Write your name in ink at the top of every page. Do not write on the back of pages. Restrict your answers to the space provided. Excessive or ambiguous answers will count against you when assigning partial credit. ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Answer the following questions with "true" or "false". Provide your reasoning for each "false" answer. Correct "true" answers are worth one point. Correct "false" answers with appropriate reasoning are worth 3 points. 1. The energy that DNA helicases use to drive the unwinding of DNA at replication forks is derived from the charge-charge interactions formed between RPA and newly single-stranded DNA. False- DNA helicases use energy derived from ATP hydrolysis to unwind DNA. The single-stranded DNA binding protein RPA protects DNA, once it has been unwound, from damage and reannealing until it can be copied by the advancing DNA polymerase. 2. One theory of the origin of introns posits that they were originally present in bacteria, but by putting a premium on rapid DNA replication, they were selected against and eventually lost. True. 3. Chain terminating nucleotides prevent further replication of DNA because they lack 5’ phosphates. False- Chain terminating nucleotides lack a 3’ hydroxyl group so that they can’t form a phosphodiester bond with the next nucleotide. If they lacked a 5’ phosphate, they could never be incorporated into nucleic acid to begin with. 4. A major source of DNA damage is due to spontaneous depurination or deamination of nucleotides. This type of damage is typically repaired via the base-excision-repair pathway. True.
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Bio115, Winter 2000 Name:_ Answers Final Exam Answers 2 5. In the nucleotide excision repair pathway, a patch of damaged DNA is removed from a chromosome and replaced by a normal DNA sequence from the homologous chromosome by gene conversion. False- In NER, a patch of DNA is removed from around the site of damage. However, the template for replacing that patch comes from the opposite strand, not from the homologous chromosome. 6. In eukaryotes, one unresolved question about the mismatch repair pathway is how the cell decides which DNA strand is mutant and which is wild-type. True- We suspect that the polarity of the DNA replication apparatus may serve as an important clue, but we don’t know for sure. 7. Exons are typically used as probes for zoo blots because they are smaller than introns and therefore easier to manipulate. False- They are used as probes for zoo blots because they are more highly conserved than introns and therefore are more likely to give a hybridization signal when do a cross- species hybridization (the zoo blot). 8. If, in a
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2000Final_key - Bio115, Winter 2000 Final Exam Answers...

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