43. A diagram of ATP synthase is shown.

If an ATP synthase contains 12 c subunits, 3 a subunits and3 ẞ subunits, how many protons must pass through this complex for every ATP molecule synthesized and transported to the cytosol, assuming that each ATP synthesized requires one proton for transport to the cytosol?

(A) 3
(B) 4
(C) 5
(D) 12
(E) 13

39. Which of the following statements about mitochondrial transport systems is(are)   correct  ? 1. Glycerophosphate shuttle converts cytosolic FADH2 to mitochondrial NADH. 　　 2. Glycerophosphate shuttle transports "NADH electron equivalents" across the mitochondrial membrane to yield 1.5 ATP/NADH. 　 3. Malate-aspartate shuttle converts cytosolic NADH to mitochondrial FADH2. 　 4. One form of glycerol-3-phosphate dehydrogenase in the glycerophosphate shuttle is a flavoprotein. 　 5. ATP-ADP translocase transfers ATP and a proton from matrix to cytosol while transferring ADP from cytosol to matrix. (A) 2 and 4 are correct. (B) 1, 3, and 5 are correct. (C) Only 5 is correct. (D) 4 and 5 are correct. (E) Only 4 is correct.

40. The oxidation of a particular hydroxy substrate to a keto product by mitochondria has a P/O ratio of less than 2. The initial oxidation step is very likely directly coupled to the: (A) reduction of a pyridine nucleotide. (B) oxidation of a flavoprotein. (C) reduction of cytochrome a3. (D) oxidation of a pyridine nucleotide. (E) reduction of a flavoprotein.

41. 2,4-Dinitrophenol and oligomycin inhibit mitochondrial oxidative phosphorylation. 2,4-Dinitrophenol is an uncoupling agent； oligomycin blocks the ATP synthesis reaction itself. Therefore,2,4-dinitrophenol will: (A) diminish O2 consumption in the presence of oligomycin. (B) block electron transfer in the presence of oligomycin. (C) allow oxidative phosphorylation in the presence of oligomycin. (D) allow electron transfer in the presence of oligomycin. (E) None of the above.

42. Consider a liver cell carrying out the oxidation of glucose under aerobic conditions. Suppose that we added a very potent and specific inhibitor of the mitochondrial ATP synthase, completely inhibiting this enzyme. Which of the following descriptions is(are)   correct  ? 1. The rate of oxygen consumption will increase.  2. ATP production in the cell will quickly drop to zero. 3. The citric acid cycle will speed up to compensate. 4. Mitochondrial ATP synthesis will cease, but to compensate, cells will accelerate the production of ATP by glycolysis, preventing ATP levels from dropping to zero. 5. The cell will switch to fatty acid oxidation as an alternative to glucose oxidation. (A) 1 and 5 are correct. (B) 3 and 4 are correct. (C) Only 2 is correct. (D) Only 4 is correct. (E) Only 5 is correct.

44. Bacteria and other prokaryotic cells have the capacity to get more ATP/glucose oxidized than eukaryotic cells because _____, so they are more efficient. (A) they have a simpler ATP synthase (B) they don't have to use shuttles to reoxidize reduced nucleotides (C) they do not have to translocate ATP-ADP across the mitochondrial membranes (D) they use an electron transport chain that translocates more protons (E) their glucose oxidation pathways are different from the pathways in eukaryotes

45. Which of the following statements about the reactions involved in the synthesis of deoxyribonucleotides is   false  ? (A) Deoxyribonucleotides are derived from the corresponding ribonucleotides by direct reduction at the 2'-carbon atom of the D-ribose to form the 2'-deoxy derivative. (B) Formation of deoxyribonucleotides is catalyzed by ribonucleotide reductase, in which its substrates are ribonucleoside diphosphates. (C) Glutathione serves as a reducing agent for glutaredoxin in deoxyribonucleotide synthesis. (D) Ribonucleotide reductase is notable in that its reaction involves free radicals in biochemical transformations. (E) The immediate precursor of thymidylate (dTMP) is dUMP. The conversion of dUMP to dTMP is a reaction of deamination.

46. Which amino acids are transaminated by the branched-chain amino acid aminotransferase? (A) valine, isoleucine, and leucine. (B) proline, valine, and alanine. (C) leucine, isoleucine, and phenylalanine. (D) leucine, isoleucine, and proline. (E) lysine, valine, and leucine.

47. Threonine is converted into acetyl-CoA and pyruvate while proline is converted into α-ketoglutarate. Classify each of these amino acids. (A) Threonine is ketogenic； proline is ketogenic. (B) Threonine is ketogenic and glucogenic； proline is ketogenic. (C) Threonine is ketogenic； proline is glucogenic. (D) Threonine is ketogenic and glucogenic； proline is glucogenic. (E) None of the above.

48. Which of the following statements explains why allopurinol is able to prevent gout? (A) It binds to uric acid thus preventing the formation of uric acid crystals. (B) It acts as a diuretic to increase the elimination of uric acid. (C) It inhibits the production of uric acid and allows for the more highly soluble xanthine and hypoxanthine to be excreted from the body. (D) It stimulates the purine salvage pathway, thus eliminating the need for production of uric acid. (E) None of the above.

49. Which of the following polarity pattern is   correct  ? (A)(B)(C)(D)(E)