23. Which form of tetrahydrofolate is used in the enzymatic transfer of formyl group, as in purine synthesis and in the formation of formyl-methionine in prokaryotes?
(A) N⁵ -Formyl-tetrahydrofolate
(B) N⁵ -Formimino-tetrahydrofolate
(C) -Formyl-tetrahydrofolate
(D)Methenyl-tetrahydrofolate
(E) Tetrahydrofolate

19. The 5´→3´ exonuclease activity of E. coli DNA polymerase I is involved in ______ during DNA replication. (A) proofreading (B) removal of RNA primers (C) sealing of nick (D) formation of Okazaki fragments (E) formation of a nick at the origin

20. Glutamate is metabolically converted to α-ketoglutarate and NH4 + in mitochondria matrix of hepatocyte by a process described as ______. (A) hydrolysis (B) transamination (C) oxidative deamination (D) one-carbon transfer (E) thiolysis

21. Posttranslational modification of proteins may include the followings EXCEPT (A) adding disulfide bridge. (B) adding cofactors and prosthetic groups. (C) cleavaging the nascent peptide. (D) adding a signal sequence at the N-terminus. (E) adding oligosaccharides in endoplasmic reticulum.

22. Which one of these characteristics is FALSE for the α-helix in protein? (A) There are 3.6 amino acids per turn. (B) There is a requirement for glycine in every third amino acid residue. (C) A H-bond forms between the carbonyl oxygen of the amino acid residue and the amido proton of the amino acid residue. (D) Proline is typically not found in the α-helix. (E) A single turn of the helix extends about 5.4 Å along the long axis.

24. Hydroxylation of proline residues in collagen is catalyzed by proly1 4-hydroxylase. The enzymatic action of prolyl 4-hydroxylase requires: ① Ascorbic acid； ② α-Ketoglutarate； ③ ； ④ ATP； ⑤ (A) ①,②,③ (B) ①,②,④ (C) ①,②,⑤ (D) ①,③,④ (E) ①,④,⑤

25. Which of the following reactions requires vitamin K? (A) carboxylation of glutamate (B) ADP ribosylation of tyrosine (C) methylation of arginine (D) oxidation of cysteine (E) amidation of C-terminus of the polypeptide

26. Which of the following proteins plays a dual role in modulating protein folding and conformation of steroid hormone receptors in eukaryotic cells? (A) CroES-CroEL complex (B) Hsp60 (C) Prefoldin (D) Hsp90 (E) Chaperonin

27. By completing β-oxidation of fatty acid with odd number of carbons, ______ will enter the citric acid cycle. ① acetyl-CoA； ② malate； ③ α-ketoglutarate； ④ succinyl-CoA (A) ①,② (B) ①,③ (C) ①,④ (D) ②,③ (E) ③,④

28. Which of the following tools is NOT used to quantify the level of gene expression? (A) real-time RT-PCR (B) RNase protection assay (C) Northern blotting (D) Western blotting (E) Southern blotting

29. Enzymes are potent catalysts because they ______. (A) are consumed in the reactions they catalyze (B) are very specific and the converted products cannot return to substrates (C) drive reactions to completion, while other catalysts drive reactions to equilibrium (D) increase the equilibrium constants for the reactions they catalyze (E) lower the activation energy for the reactions they catalyze