64. Which of the following statements regarding circulating immunoglobulins is correct?
(1) They are produced by B-cell-derived plasma cells.
(2) Their diversity is generated by gene rearrangements in the developing B cells.
(3) Each immunoglobulin producing cell generates only one kind of immunoglobulins.
(A)(1) and (2)
(B) (1) and (3)
(C) (2) and (3)
(D) None of the above is correct
(E) All of the above are correct

60. In nerves, vesicles can move the length of an axon at a rate that far exceeds that which would be predicted for simple diffusion. Which of the following models best explains vesicular movement in these cells? (A) Depolymerization of actin microfilaments attached to vesicles pulls the vesicles toward the site of depolymerization. (B) Vesicles are propelled by fluid movement generated by changes in osmotic potential within the cells. (C) Vesicles are moved by alternate contraction and relaxation of actin-myosin "muscle" complexes. (D) Vesicles, by virtue of their net negative charge, are attracted to positively charged regions of the cell. (E) Vesicles are attached to the protein kinesin, which slides along microtubules by an ATP dependent process.

61. Which kinds of the following nucleic acid can form viral genome? (1) double-stranded DNA(2) single-stranded DNA(3) single-stranded RNA (A)(1) only (B) (1) and (2) (C)(1) and(3) (D) None of the above is correct (E) All of the above are correct

62. Retroviral vectors are more popular for somatic gene therapy than other viral vectors because: (A) They replicate faster than most other viruses. (B) They contain several copies of their DNA genome in the virus particle. (C) They can integrate themselves into the host cell DNA. (D) Their replication is more accurate than that of most other viruses. (E) Their DNA has extensive sequence homology with normal cellular DNA.

63. cAMP regulates the transcription of many genes. What is the major mechanism for this action? (A) It induces the phosphorylation of transcription factors. (B) It binds directly to cAMP response elements in promoters and enhancers. (C) It mediates this effect by increasing the calcium concentration in the cytoplasm and the nucleus. (D) It binds directly to nuclear transcriptionfactors. (E) It induces the phosphorylation of STAT proteins, thus enabling them to translocate into the nucleus.

65. During long-term fasting, the liver produces acety!-CoA by the B-oxidation of fatty acids. What is the major metabolic fate of this acetyl-CoA? (A) Fatty acid biosynthesis (B) Gluconeogenesis (C) Amino acid biosynthesis (D) Ketogenesis (E) Oxidation in the TCA cycle

66. On a high-carbohydrate, low-fat diet, carbohydrates are converted into fat through a series of reactions listed below. What is the correct sequence of these reactions?(1) esterification(2) glycolysis(3) fatty acid biosynthesis (A)(1),(2),(3) (B)(1),(3),(2) (C)(2),(3),(1) (D)(2),(1),(3) (E)(3), (2),(1)

67. The molecule shown here is acetylsalicylic acid (aspirin). What kind of electrical charge does aspirin carry in the stomach at a pH value of 2 and in the small intestine at a ph value of 7?  (A) Negatively charged in the stomach； positively charged in the intestine (B) Negatively charged both in the stomach and the intestine (C) Uncharged in the stomach: negatively charged in the intestine (D) Uncharged both in the stomach and the intestine (E) Uncharged in the stomach； positively charged in the intestine

68. The brain produces most of its energy by the oxidation of glucose； during long-term fasting. however, it can cover more than half of its energy needs from__________. (A) anaerobic glycolysis (B) oxidation of its stored glycogen (C) oxidation of free fatty acids (D) oxidation of amino acids (E) oxidation of ketone bodies

69. Which of the following reactions is not the reversible reaction in glycolysis? (A) Glucose 6-phosphate to fructose 6-phosphate (B) Fructose 6-phosphate to fructose 1,6-bisphosphate (C) Glyceraldehyde 3-phosphate to 1.3-bisphosphoglycerate (D) 3-Phosphoglycerate to 2-phosphoglycerate (E) 2-Phosphoglycerate to phosphoenolpyruvate

70. Which amino acid is the common donor for methyl transfer? (A) Met (B) Ala (C)Gly (D) Ser (E) Lys