複選題

27. Please choose the   correct   answer(s) from the following descriptions: 　

1. A residue which has the dihedral angle shown below might be in an alpha-helix. 

2. Glc(α1→4)Glc linkage appears in the most abundant homopolysaccharide in the world. 　

3. Phosphorylase releases glucose-1-P from the reducing end of amylopectin. 　

4. The peptide with the sequence "AFAKLWPIEACQA" does not contain any cleavage site for cyanogen bromide. 　　

5. The amino acid "Trp" has the highest extinction coefficient at UV280 nm.
(A) 1, 3, 4 are correct.
(B) Only 2 is incorrect.
(C) 2, 5 are incorrect.
(D) 1, 4, 5 are correct. 
(E) Only 5 is correct. 

23. The brain prefers to use _____ as fuel, but under prolonged fasting or starvation it adapts to use _____.(A) fatty acids； glucose. (B) glucose； β-hydroxybutyrate. (C) glycogen； fatty acids. (D) glucose； fatty acids. (E) β-hydroxybutyrate； amino acids.

24. Given the following saturated fatty acid, how many β-oxidation cycles does it require to completely metabolize the above fatty acid to acetyl-CoA? (A) 2. (B) 3. (C) 4. (D) 5. (E) 6.

複選題25. Ketone bodies are produced by the β-oxidation of an excess of acetyl-CoA. Which of the followings are ketone bodies? ①②③④⑤(A) ①②③ (B) ①②④ (C) ②③④ (D) ②③⑤ (E) ②④⑤

26. Peptide A has amino acid sequence "CKGHNLRYEKDSAI". 　 1. Sophia used trypsin to digest the peptide. She obtained a pentapeptide. The pI of this pentapeptide is higher than 10. 　 2. Peptide A does not contain any residue with two chiral centers. 　 3. Peptide A contain only one aromatic residue. 　 4. Peptide A does not contain any residue which could be phosphorylated. 　 5. Peptide A does not contain any residue which could be modified with N-linked glycan in glycoproteins. (A) 3, 5 are correct. (B) 1, 3 are correct. (C) 1, 3, 4 are correct. (D) 1, 4 are incorrect. (E) 2, 3 are correct.

28. There are four proteins A, B, C, D. (Protein A: homotetramer, = 280,000, pI =6； Protein B: monomer, = 113,000, pI=7； Protein C: monomer, = 13,000, pI=8； Protein D is unknown). When Samuel used a gel filtration column to separate them, the elution sequence is A-D-B-C. Samuel dissolved the protein mixture in 20 mM phosphate buffer (pH 8) and loaded to a anion exchange column equilibrated with the same buffer. Protein D could not bind to this column. On an SDS-PAGE gel, protein D runs faster than protein B and slower than protein C. 1. If Samuel used SDS-PAGE to separate A, B, and C. The sequence of the protein bands shown in gel from top to bottom should be A-B-C. 　 2. The molecular mass of protein D must be between 13 and 113 kDa. 　 3. The pI of protein D might be higher than 8. 　 4. D is not a monomer. 　 5. If Samuel used 2-Dimensional electrophoresis to separate them. We could predict that the relative positions of these four proteins is like the image below.  (A) 1, 5 are correct. (D) 2, 4 are correct. (B) Only 2 is incorrect. (E) 3, 4 are correct. (C) 1, 3, 4 are correct.

29. The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics:  The for this enzyme is approximately:(A) 1 mM. (B) 2 mM. (C) 4 mM. (D) 6 mM. (E) 1000 mM.

30. Carbonic anhydrase has two substrates, carbon dioxide and bicarbonate, which are both converted to carbonic acid. Kinetic data for each is given below. While determining the kinetics of HCO3 as a substrate, how would the addition of CO2 effect the reaction if the rates were measured by the disappearance of bicarbonate? (A) CO2 would increase the activity of the enzyme. (B) CO2 would cause an apparent decrease in the (C) CO2 would act as a noncompetitive inhibitor. (D) CO2 would act as a competitive inhibitor. (E) None of the above is correct.

31. Which of the following statements regarding enzymes and transition states is   true  ? (A) Stabilization of the transition state must be less than stabilization of ES for catalysis to occur. (B) The transition state conformation of an enzyme catalyzed reaction is identical to the conformation seen in the uncatalyzed transition state. (C) Binding of substrate to an enzyme often causes strain, thus promoting transition state formation. (D) Formation of the transition state always assures that the reaction will proceed to product. (E) All are true.

32. Which of the following statements is   true   regarding enzyme pathways? (A) The most effective way to control a pathway is to regulate every enzyme in the pathway. (B) Metabolic pathways are necessary since enzymes usually catalyze only one specific reaction. (C) A regulatory enzyme is regulated only by molecules within the given pathway. (D) An enzyme pathway always proceeds in only one direction, never in reverse. (E) None of the above are true.

33. During strenuous exercise, the NADH formed in the glyceraldehyde 3-phosphate dehydrogenase reaction in skeletal muscle must be reoxidized to if glycolysis is to continue. Which of the following is the most important reaction involved in the reoxidation of NADH? (A) glucose 6-phosphate → fructose 6-phosphate (B) dihydroxyacetone phosphate → glycerol 3-phosphate (C) pyruvate → lactate (D) isocitrate → α-ketoglutarate (E) oxaloacetate → malate