23. 5-Fluorouracil (5-FU) is used to treat cancers. It is a mechanism-based inhibitor of _________.
(A) ribonucleotide reductase
(B) thymidylate synthase 
(C) adenylosuccinate lyase 
(D) GMP synthetase
(E) xanthine oxidase

19. Which two amino acids are important for ammonia assimilation(吸收) by an organism? (B) Glu and Asp (A) Glu and Gln (C) Gln and Asn (D) Lys and Trp (E) Lys and Arg

20. Which compound serves as the methy! group donor for biological methylation reactions? (A) Methyl acetate (B) Methy-tetrahydrofolate (C) S-Adenosylmethionine (D) Methanesulfonic acid (E) Methylephedrine

21. Allopurinol is a drug used to treated chronic gout(痛風) because it inhibits_______.(A) ureate oxidase (B) adenosuccinase (C) adenosine deaminase (D) xanthine oxidase (E) guanine deaminase

22. Carbamoyl phosphate synthetase I deficiency is an autosomal recessive metabolic disorder that causes __________to accumulate in the blood. (A) bicarbonate (B) ammonium (C)ADP (D) phosphate (E) CO2

24. Fatty-acid biosynthesis is vital in all biology. Which statement is correct? (A) The formation of malonyl-CoA requires micronutrient such as Mn2+. (B) The fatty-acid chain lengthening occurs either in ribosome or endoplasmic reticulum. (C) Double bonds can be introduced in Golgi body. (D) The carbon source at sites of endoplasmic reticulum is malonyl- ACP. (E) All of the above.

25. What effect would ketone bodies have on blood pH? (A) Neutralize pH (B) Lower pH (D) Fluctuate pH (E) No effect on pH (C) Increase pH

複選題26. The following figure shows the phi and psi angles of the residue X in a protein. (A) Phi angle is +45 degree. (B) Psi angle is –90 degree.(C) Phi angle is +90 degree.  (D) Psi angle is +60 degree. (E) Psi angle is +45 degree.

27. There are three proteins X, Y, and Z in 20 mM Tris (pH 7.0) solution. 1. Protein X is a homoheptamer. Its pI is 9.2. The molecular mass of each subunit of the protein X is 20,000 Da and the subunit's pl is 9.2.  2. Protein Y is a monomeric protein with molecular mass of 93,000 Da and its pl is 4.  3. Protein Z is a homodimer. Its molecular mass is 1 40,000 Da and its pI is 8. Please choose the correct answer? (A) When this mixture is loaded onto a cation exchange column, only protein Y can bind to the column: (B) When this mixture is loaded onto a size exclusion column, Protein Y is last eluted. (C) When this mixture is analyzed by a SDS- PAGE, the lowest band is protein Y. (D) When this mixture is analyzed by a SDS- PAGE, protein X and 'Z cannot be separated. (E) When this mixture is loaded onto a cation exchange column, protein X is the first eluted protein.

28. There are four peptides. Their sequences are: Peptide A : STRIKE Peptide B : ALLRIGHT Peptide C: CALENDAR Peptide D： HESSMAN The pI value of these four peptides should be (A) A＞B＞D＞C (B) C＞A＞B＞D (C) B＞A＞C>D (D) B＞A＞D＞C (E)A＞B＞C＞D

29. Because the enzymatic reaction rate is determined by the difference in energy between ES and_________ , the tighter binding of the substrate, the_________ the rate of reaction. (D) EXt; higher (A) S; higher (B) P; lower (C) EX+;lower (E) S; lower