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.

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.

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

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

複選題76. Which of the following is related to the function of proofreading step? (A) Riboswitch (B) EF-G in protein synthesis (C) Synthesis of aminoacyl-tRNA (D) RNA polymerase (E) None of the above

77. Which of the following is least related with RNA interference? (A) RISC (B) Drosha (C) Dicer (D) miRNA (E) snRNA

78. What acts as the nucleophile in the mechanism of nucleotide addition by RNA polymerase? (A) The 5' phosphate of an incoming nucleotide (B) A water molecule (C) A 5' hydroxyl of the template DNA (D) A 3' hydroxyl from the RNA being extended (E) An aspartate in the active site

79. What type of mutation causes conditions such as Huntington’s disease and Fragile X syndrome? (A) An excess of trinucleotide repeats in a protein-coding gene (B) A mutation in the p53 tumor suppressor (C) A mutation in a cyclin-dependent protein kinase (D) A mutation in the retinoblastoma gene (E) A mutation in caspase-activated DNase