3718107242 - Chemistry 3785 Sample Second Hour Exam 100...

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1 Chemistry 3785 Sample Second Hour Exam Name KEY 100 points Points Score Points Score I 48 IV 12 II 16 V 12 III 12 Total 100 I. (48) Multiple Choice. Circle the letter corresponding to the best choice. Three points each. 1. A good transition state analog: a. binds covalently to the enzyme. b. binds to the enzyme more tightly than the substrate. c. binds very weakly to the enzyme. d. is too unstable to isolate. e. must be almost identical to the substrate. 2. An uncatalyzed reaction has a rate of 4.2 × 10 -7 sec -1 . Addition of an enzyme increases the rate of reaction to 3.2 × 10 4 sec -1 . What is the rate enhancement caused by the enzyme? a. 3.2 × 10 4 b. 1.34 × 10 -2 c. 7.62 × 10 10 d. 7.4 × 10 -3 e. 1.0 × 10 11 3. Which of these groups would not make a good nucleophilic catalyst? a. amino b. carbonyl c. imidazole d. sufhydryl e. hydroxyl 4. The pK R of an amino acid is influenced by its local environment. Which environmental change would lead to an increase in the pK R of a glutamic acid side chain? a. The terminal carboxyl group is brought in close proximity to the side chain. b. The side chain of aspartate is brought into close proximity to the glutamic acid side chain. c. The glutamic acid side chain is shifted from the exterior of a protein to a hydrophobic pocket within the protein’s interior. d. All the above would increase the side chain’s pK R . e. Only a and b. 5. Three essential amino acid residues in the active site of chymotrypsin form a catalytic triad. Which of the following are roles of these residues in catalysis? a. The histidyl residue facilitates the reaction by acting as an acid-base catalyst. b. The apartate residue initiates the deacylation step by a nucleophilic attack on the carbonyl carbon of the acyl intermediate. c. The serine residue carries out a nucleophilic attack on the carbonyl carbon of the scissile peptide bond. d. All of the above are correct. e. Only a and c are correct. 6. How many stereoisomers are possible for the aldopentose D-ribose? a. 32 b. 16 c. 8 d. 4 e. 2
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2 7. Raffinose is a trisaccharide and a minor constituent in sugar beets. Its structure is shown to the right. What statement is true ? a. Raffinose consists of the three monosaccharides galactose, glucose, and fructose. b. Raffinose is a reducing sugar. c. Treatment of raffinose with β -galactosidase, an enzyme that removes galactose residues from oligosaccharides, produces 2 galactose residues and fructose. d.
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This note was uploaded on 11/24/2011 for the course BIO 400 taught by Professor Raganbower during the Winter '10 term at Drexel.

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3718107242 - Chemistry 3785 Sample Second Hour Exam 100...

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