84. Which of the following descriptions regarding genetic code is NOT correct?
(A) The genetic code is degenerate, and many codes can specify a certain amino acid.
(B) The first two positions of a codon are more important, and mutation in the third position often does not change the sense of the codon.
(C) One codon consists of three bases.
(D) Missense mutation changes only one codon and sometimes does not cause phenotypic change.
(E) Frameshift mutations can be suppressed by a suppressor tRNA molecule.

80. Which of the following statements about citric acid cycle are correct? ① Pyruvate dehydrogenase links glycolysis to the citric acid cycle. ② The products of citric acid cycle are not used for the production of ATP in cells. ③ The product of glycolysis forms acetyl-CoA for entering citric acid cycle. ④ Its intermediates are not used by other metabolic reactions. ⑤ The citric acid cycle is also called as the Krebs cycle or the tricarboxylic cycle. (A) ①②③ (B) ①②④ (C) ①②⑤ (D) ①③④ (E) ①③⑤

81. β-oxidation of fatty acids, which one of the following reactions is correct? (A) Two NADH are produced for each acetyl-CoA. (B) Oxidation of an 18-carbon fatty acid produces six molecules of propionyl-CoA. (C) Uses only even–chain, saturated fatty acids as substrates. (D) Uses NADP+ . (E) Occurs by a repeated sequence of four reactions. 

82. Which of the following is correct regarding the reaction shown below? pyruvate + HCO3 − + ATP → oxaloacetate + ADP + Pi ① It requires the direct transport of oxaloacetate across the membrane. ② It utilizes the malate-aspartate shuttle in some species. ③ It is essential for gluconeogenesis. ④ Its reactants require the function of enzymes which are only found in the cytosol. (A) ①② (B) ②③ (C) ③④ (D) ①③ (E) ②④

83. In the process of glycolysis, several reactions take place. Which of the following statements related to them are correct? ① Two molecules of pyruvate are produced by glycolysis. ② Under anaerobic condition, pyruvate can be oxidized to CO2, generating more ATP molecules. ③ Hexokinase is involved in glycolysis. ④ Frucose-1,6-biphosphate is not generated from glucose-1,6-biphosphate. ⑤ 1,3-Bisphosphoglycerate is generated from glycolysis. ⑥ Eight ATP molecules are generated from the conversion of glucose to pyruvate. (A) ②④⑤⑥ (B) ①②③④ (C) ②③④⑥ (D) ①③④⑤ (E) ①②④⑥

85. What moiety can NOT be found in a sphingomyelin? (A) Sphingosine (B) Acetylcholine (C) Ceramide (D) Fatty acid (E) Phosphoric acid

86. Which of the following compounds is NOT derivative of cholesterol? (A) Bile acids (B) Estrogens (C) Androgens (D) Glucocorticoids (E) Prostaglandins

87. Which of the following statements regarding gluconeogenesis is NOT correct? (A) Gluconeogenesis is the pathway for glucose synthesis from noncarbohydrate precursors such as lactate and pyruvate. (B) Conversion of pyruvate to phosphoenolpyruvate requires pyruvate carboxylase and phosphoenolpyruvate carboxykinase and is spontaneous. (C) Pyruvate carboxylase is mainly located in mitochondria. (D) Glycogen is the glucose-storage polymer of animals. (E) Pentose phosphate pathway provides an alternative pathway for glucose metabolism.

88. Collagen is the most abundant protein with over 28 distinct types in the animal world. What are the three necessary amino acids that exist in the mature collagens? (A) Methionine, cysteine, glycine (B) Alanine, glutamate, arginine (C) Glycine, proline, lysine (D) Methionine, phenylalanine, cysteine (E) Serine, glycine, cysteine

89. What two amino acids can be directly converted each other by a single biochemical reaction? (A) Glutamine and asparagine (B) Glycine and serine (C) Leucine and isoleucine (D) Alanine and glycine (E) Phenylalanine and alanine

90. Which of the following statements about proteins is correct? (A) Hydrogen bonds are not important in the structure of proteins. (B) Hydrophobic amino acids generally are arranged on the surface. (C) In water soluble proteins, hydrophobic amino acids are generally buried. (D) Globular proteins are generally very loosely structured. (E) Proteins consist of amino acids linked by disulfide bonds.