Queens University BCHM 218 PBA#2-QUESTIONS AND ANSWERS VERIFIED BY EXPERTS

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Question 1: (6 marks) The following diagram shows the parental DNA for two replication forks that are approaching one another from the left and right. (Note: Each linear line represents a single str... and of DNA.) (a) Annotate the diagram (inside each fork) so that it accurately shows the result of nucleotide polymerization through the action of the replisome, prior to any activity by DNA Pol I and DNA ligase. Be sure to label the polarity of all DNA polymers! (Note: you don’t need to draw the replisome proteins. Just draw the DNA that is made.) (4 marks) (b) Add DnaB to the diagram to show where it would bind and its direction of movement if ATP were added to this protein-DNA complex. (2 marks) 5’ 5’ 3’ 3’ Fork 1 Fork 2 3’ 5’ 3’ 3’ 5’ 5’ 5’ 3’ 3’ 5’ 3’ 3’ 3’ 5’ 5’ 5’ Leading strand (continuous) Lagging strand (discontinuous) Leading strand (continuous) Lagging strand (discontinuous) DnaB DnaB Newly synthesized strand Primer Primers Okazaki Fragments Okazaki Fragments Primers Primer Newly synthesized strand Question 2: (3 marks) The following diagram shows a DNA molecule with DnaB bound to one of the strands. Draw a new diagram below it to show the end result of the effect of DnaB on this DNA molecule when ATP is present. Please explain the rationale for your diagram. (3 marks) Rational DnaB is bound to the lagging strand in the 3’ to 5’ direction because of ATP energy. The ATP binds to the DNA, changing the conformation and allowing the binding of the clamp loader with the clamp. The clamp and DNA Pol III both bind to the DnaB and begin to add dNTPs. The DnaB moves along the strand in the 5’ to 3’ direction which unwinds the strand and allow replication to occur. 5’ 5’ 3’ 3’ 3’ 5’ [Show More]

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