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.

36. Which of the following is   correct   concerning the mitochondrial ATP synthase? (A) When it catalyzes the ATP synthesis reaction, the AG is actually close to zero. (B) It consists of F, and F₁ subunits, both of which are transmembrane (integral) polypeptides. (C) It can synthesize ATP after it is extracted from broken mitochondria. (D) It is actually an ATPase and only catalyzes the hydrolysis of ATP. (E) It catalyzes the formation of ATP even though the reaction has a large positive ∆Gº.

37. The NADH produced by glycolysis produces different amounts of ATP in different tissues. This is because: (A) some tissues can utilize cytosolic NADH to produce ATP； however, some tissues cannot. (B) different tissues have different energy need. (C) different tissues have different shuttle system to transport cytosolic NADH into mitochondria. (D) the efficiency of the respiratory chain in different tissues are different. (E) the averaged amounts of mitochondria in the cells of different tissues are different.

38. P/O ratio in electron transport and oxidative phosphorylation is defined as: (A) molecules of phosphate released from ATP per oxygen utilized by muscle tissue. (B) molecules of ATP formed per two electrons flowing through electron transport chain. (C) P； uptake per oxygen atom by mitochondria. (D) ratio of atoms of phosphorous to oxygen in phosphate (Pi). (E) None of the above.

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.

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.

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

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.