PS6-08answerkey - Name:_Answer Key_ TA_ Section:_ PROBLEM...

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Name:____ Answer Key _______________ TA_______________ Section:____ PROBLEM SET 6 Biochemistry 462b Spring 2008 Due March 7, 2008 Total 20 points - Answer BRIEFLY!] 1. (4 pts) Standard reduction potentials of flavins vary from protein to protein, depending upon the protein environment of the flavin. The standard reduction potential for the enzyme-bound FAD (E-FAD) in succinate dehydrogenase (Complex II, succinate-CoQ reductase) is +0.05 V: [E-FAD + 2H + + 2e - E-FADH 2 E’ o = +0.05 V] The standard reduction potential for succinate/fumarate is + 0.03 V: [Fumarate 2- + 2 H + + 2 e - succinate 2- E’ o = +0.03 V] a) [1 pt] Which redox pair has the greater tendency to lose (donate) electrons? Explain. Answer: Succinate/fumarate has a greater tendency to donate electrons (succinate is a stronger reducing agent/electron donor than is FADH2). We know this because the succinate/fumarate couple has a less positive (lower) E’ o value. b) [1 pt] Which component is the stronger oxidizing agent? Explain. Answer: FAD/FADH 2 has a greater tendency to accept electrons than fumarate/succinate (FAD is a stronger oxidizing agent than is fumarate), because FAD/FADH 2 has a more positive (i.e., a higher) E’ o value. c) [2 pts] What is the G’ o for the reduction of FAD by succinate? (Write a balanced reaction equation and show your work.) Answer: Succinate + FAD <–> Fumarate + FADH 2 G’ o = -nF E’ o G’ o = -(2)(96.5 kJ/V mol)(0.05V-0.03V) = -3.86 kJ/mol (favorable under standard conditions)
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Name:____ Answer Key _______________ TA_______________ Section:____ Page 2 2. (2 pts) The energy required to pump one proton across the mitochondrial membrane is 23 kJ/mol. For a two-electron reaction (n = 2), calculate the minimal difference in reduction potentials (in Volts) between two electron transport chain redox cofactors that is required to yield enough energy to pump one proton. ( Show all units!!!) Answer: In order to yield enough energy to transfer a proton across the membrane, -23 kJ/mol would have to be produced by an electron transfer reaction. G’
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PS6-08answerkey - Name:_Answer Key_ TA_ Section:_ PROBLEM...

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