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

 76. Degradation of amino acids can produce the precursors that are used to synthesize glucose or convert to ketone bodies. Which of the following amino acids can convert into precursors for the synthesis of glucose? 1. Leucine2.Lysine3. Cysteine4. Asparagine5. Methionine (A)123 (B) 124(C)234(D)245 (E) 345

77. A deficiency of branched chain α-keto acid dehydrogenease complex causes the defect in metabolism of amino acids. The accumulation of α-keto acid in urine leads to maple syrup urine disease. Which of the following amino acids are metabolized by α-keto acid dehydrogenease complex?            1.Methionine2.Leucine3.Isoleucine4.Valine5.Alanine (A)125(B)135(C)234(D)245(E)345

78. Defect in metabolism of phenylalanine causes phenylketounia and alkaptonuria. Which of the following statements are correct? ① A person with phenylketonuria will convert phenylalanine to phenylpyruvate. ② A person suffering from phenylketonuria on consumption food containing high phenylalanine may lead to the accumulation of tyrosine. ③ A person with phenylketonuria is advised not to consume aspartame.④ Alkaptonuria is due to defect in phenylalanine hydroxylase. ⑤ A person suffering from phenylketonuria on consumption food containing high phenylalanine may lead to the accumulation of acetoacetyl-CoA. (A)①② (B)①③ (C)①④ (D)②③ (E)②⑤

79. The de novo purine nucleotide synthesis relies upon the conversion of _______ to _______as a primary source of one carbon unit. (A) alanine; pyruvate (B) phenylalanine; tyrosine (C) serine; glycine (D) glutamate; -ketoglutarate (E) aspartate; oxaloacetate

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

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

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