31. In the enzyme catalyzed reaction sequence below, can the intermediate be predicted and why?
  
(A) Yes, the mechanism is a double-displacement reaction.
(B) Yes, the reaction fits the ping-pong model.
(C) No, the reaction is random single-displacement.
(D) No, the reaction is double-displacement.
(E) No, the reaction is 'order single-displacement.

27. Which amino acid in the above table is able to form a salt bridge with a glutamate? (A) I (B) II (C) III (E) V (D) IV

28. Which of the following statements is correct? (A) Nonpolar compounds force surrounding H2O molecules to become disordered. (B) Nonpolar compounds interfere with the hydrogen bonding among H2O molecules. (C) Nonpolar compounds increase entropy (△S) when dissolved in water. (D) Nonpolar compounds decrease enthalpy (△H) when dissolved in water. (E) None of the above

29. Compare the two reaction coordinate diagrams below and select the answer that correctly describes their relationship. In each case, the single intermediate is the ES complex. (A) (a) describes a strict "lock and key" model, whereas (b) describes a transition-state complementarity model. (B) The activation energy for the catalyzed reaction is #5 in (a) and is #7 in (b). (C) The activation energy for the uncatalyzed reaction is given by #5 + #6 in (a) and by #7 + #4 in (b). (D) The contribution of binding energy is given by #5 in (a) and by #7 in (b). (E) The ES complex is given by #2 in (a) and #3 in (b).

30. Which of the following statements regarding enzyme regulation is true? (A) Addition of an inhibitor to a V system results in kinetics similar to addition of a competitive inhibitor to a typical hyperbolic system. (B) Addition of an allosteric activator to a K system changes the plot of V vs. [S] from a sigmoidal curve to a more hyperbolic curve. (C) Allosteric effectors are always more powerful than covalent modification. (D) The I state of an enzyme generally has more activity than the R state. (E) None of the above is true.

32. An enzyme-catalyzed reaction rate will be increased if the energy level of ES can be increased. Which of the following will not increase the energy level of ES? (A) Destabilization of ES by strain caused by non-covalent interactions between E and S. (B) Loss of entropy due to binding of E and S. (C) Destabilization of ES by distortion. (D) Destabilization of ES by electrostatic effects. (E) Destabilization of Es by solvation.

33. The enzymes of the citric acid cycle are listed in the following. 1. Pyruvate dehydrogenase 2. Succinate dehydrogenase 4. Citrate synthase 5. a-ketoglutarate dehydrogenase 7. Succinyl-CoA synthase 8. Fumarase 3. Aconitatse 6. Isocitrate dehydrogenase 9. Malate dehydrogenase Which of the following descriptions is correct? (A) Enzyme 7 catalyzes the reaction that produces FADH2. (B) Enzymes 1, 5, and 9 catalyze the reactions that release CO2. (C) Enzymes 4 and 8 catalyze reactions consume H2O. (D) Enzymes 2 and 4 catalyze the reactions that consume double-bond-containing molecules. (E) Enzymes 3 and 6 catalyze the reactions that are bypassed in the glyoxylate cycle.

34. Which of the following statements about oxidation of fatty acids (FAs) is correct?  1. The energy yield per gram of FA oxidized is lesser than that per gram of carbohydrate oxidized. 2. Carnitine is used to shuttle acyl groups across the inner mitochondrial membranes.  3. Oxidation of acyl-CoA to unsaturated acyl-CoA is catalyzed by NAD-dependent acyl-CoA dehydrogenase.  4. Cleavage of the B-ketoacyl-CoA is catalyzed by thiolase. (A) 1 and 3 are correct. (B) 2 and 4 are correct. (C) 1 and 4 are correct. (D) 2 and 3 are correct. (E) All of above are correct.

35.Which of the following statements about amino acid biosynthesis is incorrect?  1. The conversion of a-ketoglutarate to glutamate is an amidation reaction. 2. Pyridoxal phosphate is a coenzyme frequently encountered in transamination reactions.  3. In animals, conversion of cysteine from serine use 3'-Phospho-5'adenylylsulfate as a sulfur donor. 4. Pyruvate generated from glycolysis can be used to synthesize alanine. (A) 1 and 3 are incorrect. (B) 2 and 4 are incorrect. (C) 1 and 4 are incorrect. (D) 2 and 3 are incorrect. (E) All of above are incorrect.

36. Which of the following statements about urea cycle is correct? 1. The urea cycle is linked to the citric acid cycle by arginine. 2. Aspartic acid is the main amino acid precursor for the carbon chain in arginine.  3. Citrulline is synthesized in the cytosol and transported to the mitochondrial matrix for subsequent reaction.  4. Ornithine is synthesized in the mitochondrial matrix and transported to the cytosol for subsequent reaction. (A) All of above are incorrect. (B) 1 and 3 are correct. (C) 2 and 4 are correct. (D) 1 and 2 are correct. (E) 3 and 4 are correct.

37. Shown is the purine catabolism. What is the chemical structure of the compound ( A )?(A)① (B)② (C)③ (D) ④(E)⑤