Quiz 6, BICH 410 (MWF3-3:50), Friday, Dec. 4, 1998
Clearly circle the letter corresponding to your answer for each problem. There are six problems, four of which count 3 points, and two for 4 points. No partial credit given for multiple-choice questions.
gas constant R 8.315 J/mole-K; Faraday constant F 96.5 kJ/mole-volt
1. Oxaloacetate uniformly labeled with 14C (i.e., with equal amounts of 14C in each of its carbon atoms) is condensed with unlabeled acetyl-CoA. After a single pass through the citric acid cycle back to oxaloacetate, what fraction of the original radioactivity will be found in the oxaloacetate?
- A) all
- B) 3/4
- C) 1/2
- D) 1/3
- E) 1/4
2. (4 pts) Which of the following is a mobile component of the electron transport chain?
- A) cytochrome c1
- B) coenzyme Q
- C) cytochrome b
- D) cytochrome a
- E) cytochrome oxidase
3. A metabolic function of the pentose phosphate pathway is:
- A) to provide intermediates for the citric acid cycle.
- B) to participate in oxidation-reduction reactions during the formation of water.
- C) to act as a source of ADP biosynthesis.
- D) to generate NADPH and pentoses for the biosynthesis of fatty acids and nucleic acids.
- E) to transport reducing equivalents of electrons across the mitochondrial inner membrane.
4. Entry of acetyl-CoA into the citric acid cycle (via pyruvate dehydrogenase) is decreased when:
- A) the ratio of [ATP]/[ADP] is high.
- B) [AMP] is high.
- C) the ratio of [NAD+]/[NADH] is high.
- D) NADH is rapidly oxidized through the respiratory chain.
- E) the ratio of [CoASH]/[acetyl-CoA] is high.
5. (4 pts) The standard reduction potentials (Eo') for the following half reactions are given.
fumarate + 2H+ + 2e- <-> succinate; Eo' = +0.031 volt
FAD + 2H+ + 2e- <-> FADH2; Eo' = -0.219 volt
If you mixed succinate, fumarate, FAD, and FADH2 together, all at 1 M concentrations and in the presence of succinate dehydrogenase, which of the following would happen initially?
Answer: D; Summed reaction written as reduction of fumarate would have deltaEo' = +0.031 + 0.219 v = +0.25 v; a positive value for deltaEo' means that the reaction is thermodynamically favorable, so fumarate would be reduced and FADH2 would be oxidized under standard conditions (1 M, each, of reactants and products)
- A) Succinate would become oxidized, FAD would become reduced.
- B) Succinate would become oxidized, FADH2 would be unchanged because it is a cofactor, not a substrate.
- C) Both fumarate and succinate would become oxidized; both FAD and FADH2 would become reduced.
- D) Fumarate would become reduced, FADH2 would become oxidized.
- E) No reaction would occur, because all reactants and products are already at their standard concentrations.
6. The conversion of 1 mole of pyruvate to 3 moles of CO2 via the citric acid cycle also yields ____ moles of NADH, ____ moles of FADH2, and ____ moles of ATP (or GTP).
Answer: E; note that starting with pyruvate, you must consider also the pyruvate dehydrogenase reaction, in which one mole of NADH is generated.
- A) 3; 2; 0
- B) 3; 1; 1
- C) 2; 2; 2
- D) 4; 2; 1
- E) 4; 1; 1