Exam_2__Fall_07__KEY

Exam_2__Fall_07__KEY - Penn State Forensics NAME KEY BMB...

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Penn State Forensics Science Serving Justice NAME: KEY BMB 400 EXAM 2 17 October 2007 100 POINTS 1. The structure below represents a replisome. Identify by name the enzymes, protein complexes, and DNA-related elements. Write your answers below, matching the names to the letters. Provide a BRIEF (one sentence) description of the role or purpose for each element. 14 Points A. Leading strand, continuously replicating B. Single Stranded Binding Protein, keeps the DNA ss’ed and extended following helicase activity and binds cooperatively to ensure rapid coverage of the ssDNA C. One or both of the following: 1) The RNA primer used to start DNA synthesis on the lagging strand, 2) An Okazaki fragment formed during non-continuous lagging strand synthesis D. Primase, an RNA polymerase used to synthesize the RNA primer to initiate synthesis on the leading or lagging strand, creating the primer template junction required for DNA polymerase E. Sliding DNA Clamp, used to hold the DNA polymerase onto the primer:template junction, enhancing processivity F. DNA Polymerase, used to synthesize DNA strands G. Helicase, used to unwind the DNA in front of the replication fork A (the 5’ strand) B C D E F G
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Page 2 BMB 400 Exam 2 17 October 2007 Initials _____________ 2. How does the Slipped-Strand Mispairing Model account for stutter at STR loci or strand slippage during replication? In the STR profile shown below, which of the peaks would you expect to be the stutter, and why? NOTE: The STR locus has a tetra-nucleotide repeat 7 Points The SSMM accounts for stutter because: 1) During the replication process the DNA polymerase can fall off the primer:template junction, 2) If this happens in the middle of an STR repeat region, the template strand may have looped out when the polymerase reassociates, causing the junction to be one repeat unit out of register, 3) The resulting product will be one repeat unit shorter than the target allele. Stutter is when an STR locus replicates during PCR and produces a product that is one repeat unit shorter than the target allele. Therefore, the peak to the left is the stutter because it is 4 bps shorter than the main peak and is smaller in peak intensity. 144 152 160 168 bps 3. What is the role of Swivelase in DNA replication, and why is it so important? 4 Points Swivelases are topoisomerases that relieve positive supercoiling generated in front of the replication fork through the action of a helicase. Through the action of Swivelases, the DNA is returned to negatively supercoiled and the replication fork will not be impeded.
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Page 3 BMB 400 Exam 2 17 October 2007 Initials _____________ 4. Polymerase fidelity is an important component of replication accuracy. Describe the ways in which DNA polymerase enhances fidelity by preventing the addition of the wrong dNTP into a newly synthesized DNA strand.
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