25. In humans, which of the following amino acids are essential?
(A) Gln and Glu.
(B) Lys and Cys.
(C) Trp and Ser.
(D) Arg and Ala.
(E) Met and Phe.

26. Choose from the answers 1~6 to describe the following figure, then pick up the correct descriptions. 1. Glc(β1→4)Glc 2. Gal(β1→4)Glc 3. Glc(α1→4)Glc4. Maltose 5. Cellobiose 6. Lactose (A) 2 and 6 are correct. (B) 1 and 4 are correct. (C) 3 and 4 are correct. (D) 1 and 5 are correct. (E) 3 and 5 are correct.

27. Please choose the correct answer from the following descriptions: 1. Number of hydrogen bonds per water molecule in ice is higher than that in water. 2. 0.1 g   glycogen   in 100 mL water results in lower osmolarity than 0.1 g   glucose   in 100 mL water. 3. Every turn of α-helix is 5.4 Å in length.  4. The strength of α-keratin depends on its Cys content. 5. Hydrogen bond in α-helix formed between residue i and i+3. (A) 1 and 3 are incorrect. (B) 2 and 5 are incorrect. (C) Only 1, 2 and 4 are correct. (D) Only 2 is incorrect. (E) Only 5 is incorrect.

28. A teacher allocates 4 peptides (peptide sequences shown below) to five students: Samuel, John, Eric, Emma, and Ramus (There are two students getting the same peptide). Peptide 1: AKLFPIEARGQA； Peptide 2: CYTTLNKTG； Peptide 3: GTGPPSGNP； Peptide 4: ASQHPMLWR Samuel says: All the residues in my peptide have only one chiral center. John says: My peptide contains many residues which do not favor α-helix structure. Eric says: My peptide does not contain the residue which can be O-glycosylated. Emma says: My peptide can be cleaved into two peptide fragments by trypsin. Ramus says: My peptide does not contain any aromatic ring. Please answer which description is correct: (A) Ramus and Eric get the same peptide. (B) Samuel gets peptide 3 and Emma gets peptide 2. (C) John and Emma get the same peptide. (D) John and Ramus get the same peptide. (E) Eric gets peptide 1 and Samuel gets peptide 2.

29. The following figure describes the torsion angle of the residue i in a protein. What do the following figures tell you? (A) The left one is ψ angle +90 degree. (B) The right one is φ angle +45 degree. (C) The left one is φ angle +90 degree. (D) The right one is φ angle +60 degree. (E) The left one is φ angle -90 degree.

30. A protein mixture contains protein A, B, C. Protein A: homodimer Mr = 180,000, pI 5； Protein B: Mr = 12,000, pI 7； Protein C: M____r = 150,000, pI 9 Joseph says: When I used SDS-PAGE to separate these three proteins. The sequence of the protein bands shown in gel from top to bottom is A-C-B. Steve says: When I used SDS-PAGE to separate these three proteins. The sequence of the protein bands shown in gel from top to bottom is B-A-C Jacky says: When I dissolved the protein mixture in 20 mM phosphate buffer (pH 7) and loaded it to a cation exchange column equilibrated with the same buffer. Only protein C could bind to the column matrix Simon says: When I dissolved the protein mixture in 20 mM phosphate buffer (pH 8) and loaded it to an anion exchange column equilibrated with the same buffer. Only protein C could bind to the column matrix Clarence says: When I dissolved the protein mixture in 150 mM phosphate buffer (pH 7) and used a gel filtration column to separate them, the elution sequence is B→C→A. Rita says: When I dissolved the protein mixture in 150 mM phosphate buffer (pH 7) and used a gel filtration column to separate them, the elution sequence is A→C→B. Lily says: When I dissolved the protein mixture in 150 mM phosphate buffer (pH 7) and used a gel filtration column to separate them, the elution sequence is C→A→B. Who are correct? (A) Joseph, Simon, and Clarence. (D) Simon and Clarence. (B) Rita and Jacky. (E) Joseph, Jacky, and Rita. (C) Steve, Jacky, and Lily.

31. There are three peptides, A, B, and C. Peptide A sequence is DSQWMKLGIV. Peptide B sequence is KLHPPGTI. Peptide C sequence is EETAIRR. Amelia says: The pI value of peptide A should be near 9. David says: The pI value of peptide C is higher than peptide B. Bret says: The pI value of peptide B should be near 6. Sandy says: The pI value of peptide B is higher than peptide A. Who is correct? (A) Amelia. (B) All are incorrect. (C) David. (D) Bret. (E) Sandy.

32. A small molecule that increases the activity of an enzyme by binding to a site other than the catalytic site is termed a(n): (A) allosteric activator. (B) alternative inhibitor. (C) competitive activator. (D) stereospecific agent. (E) transition-state analog.

33. Which of these statements about enzyme-catalyzed reactions is   false  ? (A) At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration. (B) If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor. (C) The rate of a reaction decreases steadily with time as substrate is depleted. (D) The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction. (E) The Michaelis-Menten constant equals the [S] at which V = 1/2

34. When every enzyme molecule in the reaction mixture has its substrate-binding site occupied by substrate, the kinetics become _____ -order, and the velocity is _____. (A)(B) (C)(D) (E)

35. All are properties of regulatory enzymes   except  : (A) pathway end-products may act as allosteric inhibitors. (B) v vs [S] plots are sigmoid- or S-shaped. (C) monomeric enzymes with a single regulated active site. (D) substrate binding is cooperative. (E) may be stimulated by allosteric activators.

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