Exam 3 Study Questions

Exam 3 Study Questions - EXAM 3 STUDY QUESTIONS(version2...

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EXAM 3 STUDY QUESTIONS (version 2, 11/7/08) 1.  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? Promoter sequence contains -35 box and -10 box in bacteria. Promoter sequence found on the non-template strand, about 40 to 50 base pair long and has similar in certain sections. Also, similar DNA has bases common to TATAAT, also know as -10 box. -10 box is 10 bases from the point where RNA polymerase begins transcription. +1 site is where transcription begins. TTGACA happens to be in the same promoters which were about 35 bases upstream from the +1 site, also know as -35 box. Basically, transcription begins when sigma which was part of the holoenzyme complex binds -35 and -10 boxes. The role sigma factor appeared to be responsible for leading RNA polymerase to exact locations where transcription will begins. 2.  What happens during the “elongation phase” of transcription?  How does transcription  end? During the elongation phase of transcription, RNA polymerase moves along the DNA template in 3’-----5’ direction of the template strand, synthesizing RNA in the 5’-----3’ directions. Transcription ends with a termination phase. Basically, transcription would stops when RNA polymerase gets to a point where a stretch of DNA sequence that works as a transcription signal. Transcription ends when termination signal at the end of the gene guide to the arrangement of a hairpin in the mRNA and interrupting the transcription complex. 3.  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? 4.  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? 5.   What was Crick’s “adapter molecule” and how was it discovered?  What is an  “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. p. 1
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6.  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? 7.  What are the three phases of protein synthesis (translation)?  How do mRNAs and 
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Exam 3 Study Questions - EXAM 3 STUDY QUESTIONS(version2...

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