practice_final_exam_2

practice_final_exam_2 - Name CHM 3218 CHM 5305 Summer 2011...

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__________________________________ Name 1 CHM 3218 / CHM 5305 Summer 2011 Practice Final Examination – Part 2 University of Florida Honor Code Statement: "On my honor, I have neither given nor received unauthorized aid in doing this assignment." __________________________________ Student signature Instructions : You would have 75 minutes to complete this section of the exam. All books, notes and other aids would be prohibited, but calculators and molecular models would be allowed (no sharing of calculators or molecular models, however). Be sure to budget your time and answer questions briefly but completely. To receive partial credit for incorrect answers, be sure to show your work, particularly in problems involving calculations. Write your name on each page. 1. A bacterial ribonucleotide reductase catalyzes the NADPH-dependent reduction of the 2'- hydroxyl of nucleotide triphosphates to the corresponding deoxyribonucleotide triphosphates for later incorporation into DNA. ( Total 9 points ). O O P HO OH B P B = any base P + NADPH + H + ribonucleotide reductase O O P HO B P P + NADP + + H 2 O a. What is the value of Δ E º' for this reaction? ( 4 points ).
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__________________________________ Name 2 b. The currently-accepted mechanism for ribonucleotide reductase involves radical intermediates. Formation of a disulfide bond on the enzyme has been suggested to provide the reducing power for the ribonucleotide reduction (step 1), then this protein disulfide bond is supposed to be reduced by NADPH to regenerate the reduced form of the enzyme needed for subsequent turnovers (step 2). Is the proposed two-step sequence shown below thermodynamically feasible? Justify your answer with a calculation that clearly illustrates your logic. ( 5 points ). O O P HO OH B P B = any base P + Protein disulfide reduced O O P HO B P P + Protein disulfide oxidized Protein disulfide oxidized + NADPH + H + Protein disulfide reduced + NADP + Step 1: Step 2:
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__________________________________ Name 3 2. A simplified scheme for oxidative phosphorylation is shown below. Use your knowledge of these reactions to answer the following questions. For all of these questions, you may
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practice_final_exam_2 - Name CHM 3218 CHM 5305 Summer 2011...

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