18. Which amino acid is the precursor of the methyl group donor in biological methylation?
(A) Tryptophan.
(B) Histidine.
(C) Methionine.
(D) Arginine.
(E) Lysine.

14. ATP made in glycolysis and the TCA cycle is the result of _____ phosphorylation, and NADH-dependent ATP synthesis is the result of _____ phosphorylation. (A) oxidative； substrate-level. (B) oxidative； electron. (C) substrate-level； electron. (D) substrate-level； oxidative. (E) proton-gradient； oxidative.

15. Phenylketonuria (PKU) results from a disorder of the metabolism of: (A) branched-chain amino acid. (B) glutamic acid. (C) phenylalanine. (D) cysteine. (E) dopa.

16. Adipokines are cytokines (cell signaling proteins) secreted by the adipose tissue. Which factor is   not   an adipokine: (A) Leptin. (B) Adiponectin. (C) TNFa. (D) Resistin. (E) Ghrelin.

17. Aminotransferases are enzymes that have all of the following characteristics   except  : (A) can make an α-keto acid from an α-amino acid. (B) use pyridoxal phosphate as a carrier of amino groups. (C) catalyze highly reversible reactions. (D) use ATP. (E) serum levels are used as a clinical measure of tissue damage.

19. What situation is most likely to the formation of ketone bodies? (A) Starvation. (B) Diabetes not suitably controlled. (C) Intake high in lipids, low in carbohydrates. (D) All of the above. (E) None of the above.

20. What effect do ketone bodies have on blood pH? (A) Lower blood pH. (B) Increase blood pH. (C) Neutralize blood pH. (D) No effect on blood pH. (E) Can't determine.

21. Which statement is   correct   for fatty acid biosynthesis? (A) Double bonds can be introduced in Golgi body. (B) Chain lengthening occurs either in ribosome or endoplasmic reticulum. (C) The carbon source at site of endoplasmic reticulum is malonyl-ACP. (D) Ribosome is the principle enzyme for fatty acid biosynthesis. (E) Carbon dioxide is involved in the formation of malonyl-CoA.

22. Where does the fatty acid synthesis occur in the cell? (A) Autophagosome. (B) Cytoplasm. (C) Mitochondrial matrix. (D) Golgi body. (E) Inner mitochondrial membrane.

23. In analytical ultracentrifugation the sedimentation coefficient, which is expressed in Svedberg units (S), characterizes a sedimenting particle on the basis of: (A) size only. (B) shape only. (C) charge only. (D) both size and shape. (E) None of these.

24. Which of the following statements is   true  ? (A) In order to replicate both DNA strands, E. coli synthesizes each strand in the opposite direction (one 5'-3', one 3'-5'), so they can be synthesized at once. (B) Okazaki fragments are short DNA pieces that explain how DNA is synthesized on the leading strand. (C) A primer strand in DNA replication is needed because it ensures the fidelity of the newly synthesized DNA strand. (D) DNA repair mechanisms are essentially the same whether the DNA has minor damage or major damage.