69. Topoisomerases:
(A) can change the linking number in increments of 1 or 2.
(B) can act on single-stranded DNA circles.
(C) change the degree of supercoiling of a DNA molecule but not its linking number of DNA.
(D) occur in bacteria, but not in eukaryotes.
(E) always require energy from ATP.

65. Pyruvate is oxidized to produce ________, which further reacts with ________ to produce ________ during the citric acid cycle. (A) citrate; fumarate; α-ketoglutarate (B) citrate; isocitrate; α-ketoglutarate (C) acetyl-CoA; oxaloacetate; citrate (D) acetyl-CoA; malate; oxaloacetate (E) malate; citrate; acetyl-CoA

66. Phosphate (Pi) is transported into the mitochondria from the cytosol by a phosphate carrier which is driven by the ________. (A) hydrolysis of ATP (B) simultaneous transport of H+ into the mitochondrion (C) simultaneous transport of ADP into the mitochondrion (D) simultaneous transport of H+ out of the mitochondrion (E) simultaneous transport of ATP out of the mitochondrion

67. When monosaccharide dissolves in water at 40°C, it can undergo interconversion between α and β forms automatically. Which of the following regarding the amount of each form is correct after equilibrium? (A) β-D-Ribofuranose ＞ β-D-Ribopyranose (B) α-D-Fructofuranose ＞ β-D-Fructofuranose (C) β-D-Fructofuranose ＞ β-D-Fructopyranose (D) β-D-Glucopyranose ＞ α-D-Glucopyranose (E) None of the above

68. Phospholipase C hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to form which signaling molecule that triggers Ca2+ release from the endoplasmic reticulum? (A) Diacylglycerolphosphate (DAGP) (B) Inositol 5-monophosphate (IP1) (C) Diacylglycerol (DAG) (D) Inositol 1,4,5-triphosphate (IP3) (E) Inositol 4,5-bisphosphate (IP2)

70. The ion channel that opens in response to acetylcholine is an example of a ________ signal transduction system. (A) G-protein (B) ligand-gated (C) receptor-enzyme (D) serpentine receptor (E) voltage-gated

71. The energy of a photon absorbed by an antenna molecule of the photosystem finds its way to a chlorophyll molecule in the reaction center of a light-harvesting complex by a process of ________. Which of the following is the best choice? (A) electron transfer (B) fluorescence re-radiation (C) resonance transfer (D) resonance transfer and electron transfer (E) electron transfer and fluorescence re-radiation

72. In the erythrocyte, glycolysis produces ________that is further metabolized to ________. (A) lactate; acetyl-CoA (B) lactate; pyruvate (C) pyruvate; acetyl-CoA (D) pyruvate; lactate (E) pyruvate; oxaloacetate

73. What role does AP endonuclease have in the base-excision repair system? (A) It removes the damaged base from the nucleic acid. (B) It cleaves the phosphodiester backbone after base removal. (C) It removes nucleotides from the broken strand of the nucleic acid. (D) It adds new nucleotides to replace the excised ones. (E) It creates a new phosphodiester bond to repair the backbone.

74. Restriction-modification systems: (A) exist in all organisms as a protection against foreign DNA invasion. (B) include a site-specific exonuclease to degrade foreign DNA. (C) modify DNA by acetylation. (D) include a DNA methylase and an endonuclease. (E) include three types of endonuclease all of which cleave within a specific DNA target sequence.

75. DNA polymerase I synthesizes new DNA with very high fidelity, due to its ________. (A) high processivity (B) 3'→5' exonuclease activity (C) helicase association with the primase (D) 5'→3' exonuclease activity (E) all of the above