27. Which of the following statements about protein-ligand binding is   correct  ?
(A) The (association constant) is equal to the concentration of ligand when all of the binding sites are occupied.
(B) The is independent of such conditions as salt concentration and pH.
(C) The larger the , the weaker the affinity.
(D) The larger the , the smaller the (dissociation constant).
(E) The larger the , the faster the binding.

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.

25. The cyclic form of sugars (A) has one more chiral center than the open-chain form. (B) loses a chiral center compared to the open-chain form. (C) is not usually found in nature. (D) has one more carbon atom than the open-chain form. (E) has one less carbon atom than the open-chain form.

複選題26. Mr. Bean synthesizes a pentapeptide "DPRTH". Choose the   correct   answer from the following descriptions (pK₂ of the N-terminal amino group of the peptide is 9.1； pK₁ of the C-terminal carboxyl group of the peptide is 2.1； pKa of D is 3.65, pKa of R is 12.5, pKa of H is 6): (A) The pI value of the peptide is around 4. (B) The pI value of the peptide is around 7. (C) The pI value of the peptide is around 11. (D) When 0.1 mg of the peptide is dissolved in 100 mM Tris (pH 9), it could bind to a cation exchange column. (E) All the residues in this peptide contain one chiral center only.

28. Which of the following statements regarding enzyme regulation is   true  ? (A) Addition of an inhibitor to a V system results in kinetics similar to addition of a competitive inhibitor to a typical hyperbolic system. (B) Addition of an allosteric activator to a K system changes the plot of V vs. [S] from a sigmoidal curve to a more hyperbolic curve. (C) Allosteric effectors are always more powerful than covalent modification. (D) The T state of an enzyme generally has more activity than the R state. (E) None of the above are true.

29. In the enzyme catalyzed reaction sequence below, can the E-PO4- intermediate be predicted and why? (A) yes, the mechanism is a double-displacement reaction. (B) yes, the reaction fits the ping-pong model. (C) no, the reaction is random single-displacement. (D) no, the reaction is double-displacement. (E) no, the reaction is order single-displacement.

30. An enzyme-catalyzed reaction rate will be increased if the energy level of ES can be increased. Which of the following will   not   increase the energy level of ES? (A) destabilization of ES by strain caused by non-covalent interactions between E and S. (B) loss of entropy due to binding of E and S. (C) destabilization of ES by distortion. (D) destabilization of ES by electrostatic effects. (E) destabilization of ES by solvation.

31. The T form (tense or taut form) of deoxyhemoglobin differs from oxyhemoglobin (the R form or relaxed form) by all   except  : (A) covalent linkages between subunits. (B) specific intrachain hydrogen bonds. (C) between β-subunit salt links (ion-pair bonds). (D) between a-subunits salt links (ion-pair bonds). (E) intrachain salt bridges.

32. The power stroke in muscle contraction is associated with: (A) the binding of ATP to ATPase. (B) the hydrolysis of ATP. (C) binding of myosin to actin. (D) addition of water for ATP hydrolysis. (E) the dissociation of ADP and Pi from the ATPase.

33. Which of the following four statements regarding glycolysis and gluconeogenesis is   correct  ? (1) Substrate-level phosphorylation occurs when conversion of1,3-bisphosphoglycerate to 3-phosphoglycerate occurs. (2) The only oxidative reaction in glycolysis is the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate. (3) The phosphofructokinase-1 catalyzes the glycolytic reaction step that is irreversible in gluconeogenesis. (4) If fructose-2,6-bisphosphate is low, glycolysis proceeds； if fructose-2,6-bisphosphate is high, gluconeogenesis proceeds. (A) (1), (2), and (4) are correct. (B) (1), (3), and (4) are correct. (C) (1), (2), and (3) are correct. (D) (2), (3), and (4) are correct. (E) All are correct.