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Unformatted text preview: EXAM 3 STUDY QUEST IONS (version 2, 4/18/08) 1. How does DNA polymerase III accomplish DNA synthesis? Why is an RNA primer needed? What does it mean to say that DNA is synthesized in the 5 to 3 direction? 2. The error rate during DNA replication averages less than one mistake per billion nucleotides (error rate < 1 x 10-9 ). How is this extremely low error rate achieved? What happens when a DNA polymerase inserts the wrong base into a sequence? Explain proofreading by DNA Pol III and mismatched base repair. 3. Can DNA be repaired if it is damaged? If repair is possible, when does it occur? before, during, or after DNA replication (S-phase)? (NOTE: the choices are not mutually exclusive; it could be one, or two or all three.) How do you know if your answer is correct? Where could you go to find out? ------------------------------------------------------- 4. What does a promoter sequence do in bacteria? What are the two boxes and why are they important? What is the role of the sigma factor? There is typically more than one type of sigma factor in most species of bacteria. Why? 5. In eukaryotes there are at least three different RNA polymerase enzymes. What does each of them do? What would the result be if there were a deletion mutation in RNA pol I, RNA pol II, or RNA pol III? How does the initial mRNA transcript differ in eukaryotes and bacteria? 6. Eukaryotic mRNA that leaves the nucleus and enters the cytoplasm has been processed in a number of ways. What happens during splicing and why is splicing needed? What feature(s) of the mRNA that enters the cytoplasm make the mRNA last longer? 7. What was Cricks adapter molecule and how was it discovered? What is an p. 1 anticodon? How many different codons are there (chap 15)? How many different anticodons are there? [Hint: How many types of tRNA are there?] Explain what accounts for the difference. 8. There must be at least N different aminoacyl tRNA snythetases. How many is N ? Why that many? What do these enzymes do? What would be the effect if a mutation in the gene for a particular aminoacyl tRNA synthetase caused the enzyme to become completely non-functional?...
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