84. Which DNA repair system is likely to be used in repairing DNA with an uracil residue?
(A) Base-excision repair
(B) Mismatch repair
(C) Direct repair
(D) Nucleotide-excision repair
(E) Recombinational DNA repair

80. Which of the following statements for thermal denatuation of DNA are false?1. The absorption of ultraviolet at 260 nm increases.2.The DNA helical structure unwinds. 3. The covalent N-glycosidic bond between the base and the deoxyribose breaks. 4.The melting temperature of DNA with 60% A+T content is lower than that with 20% G+C content. 5.The double-helical DNA becomes single-stranded DNA at melting temperature. (A)135(B)134(C)145(D)234(E)345

81. Which of the following enzymes does not require a template? (A) RNA polymerase II(B) DNA polymerase (C) Polyadenylate polymerase(D) Telomerase (E) Reverse transcriptase

82. Which is not a true statement about reverse transcriptase? (A) The direction of polynucleotide synthesis is 5' → 3'. (B) It has 3' → 5' exonuclease activity. (C) It synthesizes DNA complementary to an RNA template. (D) It synthesizes DNA complementary to a DNA template. (E) It degrades the RNA strand of the RNA-DNA hybrid.

83. Many proteins are involved in DNA replication of E. coli. Which of the following pairs of protein and function are correct? ①DNA gyrase, unwinding DNA ②DnaA, helicase ③DNA polymerase I, excises RNA primer and fills in with DNA④DNA polymerase II holoenzyme, 5' → 3' exonuclease⑤DNA polymerase III holoenzyme, elongation (DNA synthesis) (A)②③⑤(B)②③④(C)①③④(D)①③⑤(E)①①⑤

85. Aptamers are _______. (A) double-stranded RNA products of nuclease action on hairpin RNAs (B) repeat sequence elements at the ends of transposons (C) small RNA molecules selected for tight binding to specific molecular targets (D) the RNA primers required for retroviral replication (E) the short tandem repeat units found in telomeres

86. Which of the following modification elucidates the inhibitory effect of diphtheria toxin on the function of eukaryotic translation factor eEF2? (A) Phosphorylation (B) Dephosphorylation (C) ADP-ribosylation (D) Prenylation(E) S-Nitrosylation

87. Elongation factor Tu (EF-Tu): (A) binds GTP promoting translocation of ribosomes along mRNA (B) displaces GDP from the elongation complex (C) binds aminoacyl-tRNA in the presence of GTP (D) binds initiator tRNA and GTP (E) binds to 30S subunit and drives mRNA binding

88. Selenocysteine (Sec) and pyrrolysine (Pyl) are recognized as 21st and 22nd amino acids, respectively. tRNASec and tRNAPyl have anticodon pairing with _______ and _______, respectively. (A) UAA, CUG(B) UGA, UAG(C) UAA, UAG(D) UAG, UGA(E) UAG, UAA

89. Which step about regulation of gene expression by insulin is not correct? (A) Insulin receptor binds insulin and undergoes autophosphorylation. (B) Insulin receptor binds IRS-1 on its Tyr residues. SH3 domain of Grb2 binds to phosphorylated Tyr of IRS-1. (C) Sos binds to Grb2, then to Ras, causing GDP release and GTP binding to Ras. (D) Activated Ras binds and activates Raf-1. (E) Raf-1 phosphorylates MEK. MEK phosphorylates MAPK, activating it.

90Which description about β-adrenergic pathway (a G-protein coupling receptor; GPCR) is not correct? (A) The receptor is a 7-transmembrane protein. (B) Epinephrine binds to a GPCR. (C) The occupied receptor could cause the replacement of the GDP bound to GS (stimulatory G protein) by GTP, activating GS. (D) GSβ moves to adenylyl cyclase and activates it to synthesize cAMP. (E) cAMP activates PKA to trigger cellular response.