32. Which of the following statements is   true   regarding enzyme pathways?
(A) The most effective way to control a pathway is to regulate every enzyme in the pathway.
(B) Metabolic pathways are necessary since enzymes usually catalyze only one specific reaction.
(C) A regulatory enzyme is regulated only by molecules within the given pathway.
(D) An enzyme pathway always proceeds in only one direction, never in reverse.
(E) None of the above are true.

28. There are four proteins A, B, C, D. (Protein A: homotetramer, = 280,000, pI =6； Protein B: monomer, = 113,000, pI=7； Protein C: monomer, = 13,000, pI=8； Protein D is unknown). When Samuel used a gel filtration column to separate them, the elution sequence is A-D-B-C. Samuel dissolved the protein mixture in 20 mM phosphate buffer (pH 8) and loaded to a anion exchange column equilibrated with the same buffer. Protein D could not bind to this column. On an SDS-PAGE gel, protein D runs faster than protein B and slower than protein C. 1. If Samuel used SDS-PAGE to separate A, B, and C. The sequence of the protein bands shown in gel from top to bottom should be A-B-C. 　 2. The molecular mass of protein D must be between 13 and 113 kDa. 　 3. The pI of protein D might be higher than 8. 　 4. D is not a monomer. 　 5. If Samuel used 2-Dimensional electrophoresis to separate them. We could predict that the relative positions of these four proteins is like the image below.  (A) 1, 5 are correct. (D) 2, 4 are correct. (B) Only 2 is incorrect. (E) 3, 4 are correct. (C) 1, 3, 4 are correct.

29. The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics:  The for this enzyme is approximately:(A) 1 mM. (B) 2 mM. (C) 4 mM. (D) 6 mM. (E) 1000 mM.

30. Carbonic anhydrase has two substrates, carbon dioxide and bicarbonate, which are both converted to carbonic acid. Kinetic data for each is given below. While determining the kinetics of HCO3 as a substrate, how would the addition of CO2 effect the reaction if the rates were measured by the disappearance of bicarbonate? (A) CO2 would increase the activity of the enzyme. (B) CO2 would cause an apparent decrease in the (C) CO2 would act as a noncompetitive inhibitor. (D) CO2 would act as a competitive inhibitor. (E) None of the above is correct.

31. Which of the following statements regarding enzymes and transition states is   true  ? (A) Stabilization of the transition state must be less than stabilization of ES for catalysis to occur. (B) The transition state conformation of an enzyme catalyzed reaction is identical to the conformation seen in the uncatalyzed transition state. (C) Binding of substrate to an enzyme often causes strain, thus promoting transition state formation. (D) Formation of the transition state always assures that the reaction will proceed to product. (E) All are true.

33. During strenuous exercise, the NADH formed in the glyceraldehyde 3-phosphate dehydrogenase reaction in skeletal muscle must be reoxidized to if glycolysis is to continue. Which of the following is the most important reaction involved in the reoxidation of NADH? (A) glucose 6-phosphate → fructose 6-phosphate (B) dihydroxyacetone phosphate → glycerol 3-phosphate (C) pyruvate → lactate (D) isocitrate → α-ketoglutarate (E) oxaloacetate → malate

34. In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change of 23.8 kJ/mol. Under what conditions (encountered in a normal cell) will the free-energy change (AG) be negative, enabling the reaction to proceed to the right? (A) Under standard conditions, enough energy is released to drive the reaction to the right. (B) If the concentrations of the two products are high relative to that of fructose 1,6-bisphosphate. (C) The reaction will not go to the right spontaneously under any conditions because the is positive. (D) When there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products. (E) None of the above.

35. In normal mitochondria which statement regarding the rate of NADH consumption is   correct  ? 　 1. Be increased in active muscle, decreased in inactive muscle. 　 2. Be very low if the ATP synthase is inhibited, but increase when an uncoupler is added. 　 3. Decrease if mitochondrial ADP is depleted. 　 4. Decrease when cyanide is used to prevent electron transfer through the cytochrome a + a3 complex. (A) 1, 2, and 3 are correct. (B) 1, 3, and 4 are correct. (C) 2, 3, and 4 are correct. (D) 1, 2, and 4 are correct. (E) All are correct.

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.