67. The symptoms of severe combined immunodeficiency syndrome (SCID) are caused by a deficiency of which of the following enzymes?
(A) adenine phosphoribosyltransferase
(B) HGPRT (hypoxanthine-guanine phosphoribosyltransferase)
(C) adenosine deaminase
(D) dihydrofolate reductase
(E) xanthine oxidase

64. Glycogen, amylose, and amylopectin are storage polysaccharides. Which one is linear form? (A) Glycogen (B) Amylose (C) Amylopectin (D) All of the above (E) None of the above

65. Which of the following statements about protein-ligand binding is correct? (A) The Ka is equal to the concentration of ligand when all of the binding sites are occupied. (B) The Ka is independent of such conditions as salt concentration and pH. (C) The larger the Ka (association constant), the weaker the affinity. (D) The larger the Ka, the faster is the binding. (E) The larger the Ka, the smaller the Kd (dissociation constant).

66. Which of the following is a heteropolysaccharide? (A) Cellulose (B) Chitin (C) Glycogen (D) Hyaluronate (E) Starch

68. Transport of fatty acids from the cytoplasm to the mitochondrial matrix requires: (A) ATP, carnitine, and coenzyme A.(B) ATP, carnitine, and pyruvate dehydrogenase. (C) ATP, coenzyme A, and hexokinase. (D) ATP, coenzyme A, and pyruvate dehydrogenase. (E) carnitine, coenzyme A, and hexokinase.

69. Which of the following enzymes is inhibited by malonyl-CoA? (A) Fatty acid synthase (B) Acetyl-CoA carboxylase (C) Hormone-sensitive lipase (D) Carnitine acyltransferase-1 (E) Hydroxymethylglutary1 CoA reductase

70. What is the CORRECT sequence of events involving cyclic AMP as a second messenger of glucagon hormone? I. the stimulation of the activity of adenylate cyclase. II. the activation of G-proteins.III. the conversion of ATP to cyclic AMP.IV. the activation of protein kinase A. V. the stimulation of lipid mobilization.VI. an increase in the activity of hormone-sensitive lipase. (A) II, I, III, VI, IV, V (B) II. I, III, IV, V, VI (C) II, I, IV, III, V, VI (D) II, I, III, IV, VI, V (E) II, I, IV, III, VI, V

71.When the amino group has been removed from an amino acid, the carbon skeleton or a-keto acid may be used in many different ways. Which of the following is NOT a possible fate for the carbon skeleton? (A) conversion to glucose (B) oxidation for energy (C) synthesis of fat (D) synthesis of creatine (E) synthesis of ketones

72. Which process is NOT a source of ammonia in the body? (A) urea formation in the liver (B) deamination of amide groups from glutamine (C) degradation of pyrimidines (D) bacterial lysis of urea and amino acids in the GI tract (E) complete oxidation of amino acids

73 Reduction of the carbonyI group on a sugar rise to the class of polyhydroxy compounds called alditols. Important naturally occurring ones are erythritol, D-mannitol, and D-glucitol, often called sorbitol. When sorbitol accumulates in the lens of the eye of a person with diabetes, it can lead to the formation  of________.(A) Glaucoma(B) Amblyopia (C) Cataract (D) Strabismus (E) None of the above

74. Enzyme kinetics provide the values of the Michaelis constant KM and the turnover number Kcat. Which of the following statements is true? (A) KM indicates the substrate concentration at which the reaction rate is Vmax (B) KM measures the rate of the catalytic process (C) KM indicates the substrate binding affinity； the smaller KM indicates the higher substrate binding affinity (D) In enzyme inhibition study, a competitive inhibitor decreases the apparent KM (E) All of the above