Download Problem Set 3A

Problem Set 3A
Name and Lab Section:_____________________
Due 10-16-06 at beginning of lecture
1. (Read the first 3 questions before you do any of them.) Draw a section of the E. coli
chromosome as replication is occurring through that region. Give yourself plenty of
room and make the replication bubble stretch most of the way from one side of your
paper to the other. Show both replication forks and a bit of DNA at each end that has not
yet been replicated. Use single long arrows for each of the original DNA strands, being
sure with all DNA and RNA strands that the arrows are oriented correctly to signify the
5’ and 3’ ends of the molecules. Identify the origin of replication with “ori.” Use long
arrows to signify the leading strands; wavy arrows (or wavy parts of lines) to signify
RNA primers; and short arrows to signify lagging strand DNA.
2. List (and number) 8 enzymes known to be involved in DNA replication in E. coli and
give a single phrase, or sentence description that distinguishes what each of them does.
The description should have enough detail to distinguish each enzyme from any of the
others involved in DNA synthesis.
3. In the figure you have drawn for question 1, place a number encoding a most likely
location where each of the above enzymes would be functioning at the time of the
drawing.
4. What does telomerase use as template for synthesizing more DNA on the ends of chromosomes?
What does it use as primer?
5. Why do Ds elements need the presence of an Ac element in order to transpose?
6. What is the function and structure of most centromeres?
7. In the process of sequencing a portion of an organism’s genome, you identify a number of
regions of about 6 kb (kilobases), each of which has direct repeats at the ends of it. The direct
repeats are unique for each of these regions. For each element, just inside of the direct repeat
at one end is a region with 40-50 A’s in a row (polyA repeat). You find a relatively long ORF
(open reading frame) in the 6 kb region. What does that ORF probably encode? What does
this tell you about the nature of the nucleic acids which moved each of these elements to their
present location?
8. List four types of middle repetitive DNA in eukaryotic genomes.
9. What type of exonuclease activity do DNA polymerases that can do proofreading have?
Why does that activity increase the accuracy of DNA replication?
10. What are the four things that enzymes involved in recombination probably need to be able
to do?
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