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Unformatted text preview: BC 367 Exam 2- November 17, 2005 Name____________________ Part I- Multiple Choice (36 points)- Choose the single most correct answer. 1. In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by: __ A. __ B. __ C. __ D. __ E. 2. binding of CO2. H + produced during metabolism. formation of specific ion pair interactions. increased levels of BPG. oxygen binding. Which of the following is correct concerning oxygen binding to hemoglobin? __ A. __ B. __ C. __ D. __ E. Addition of the third O2 is more difficult than addition of the second. The "Bore Effect" refers to the inhibition of oxygen delivery and subsequent drowsiness that ensues during long-winded lectures. The binding of O2 changes the valence of the iron in heme. The binding of CO increases O2 affinity. O 2 binds with reduced affinity to fetal hemoglobin relative to adult hemoglobin. 3. Compare the two reaction coordinate diagrams below and select the answer that correctly describes their relationship. In each case the single intermediate is the ES complex. __ A. __ B. __ C. __ D. __ E. 2 is at lower energy than 4 because 2 has decreased entropy relative to 4 . The activation energy for the c atalyzed reaction is 5 in (a) and is 7 in (b). (a) describes a strict "lock and key" model whereas (b) describes a transition-state complementarity model. The catalyzed reaction in (a) should be faster than the catalyzed reaction in (b). The ES binding energy is given by 5 in (a) and by 8 in (b). 1 4. Which of the following statements about lysozyme is not true? __ A. __ B. __ C. __ D. __ E. Its substrate is the polysaccharide component of bacterial cell walls. The active site Glu has an unusually high pKa. The role of the active site Asp may be stabilize the carbocation intermediate or to attack the glycosidic carbon. It is similar in structure and mechanism to other serine proteases. Catalysis involves substrate distortion. 5. Which of the following parameters remains the same for S -->P, whether the reaction is enzyme-catalyzed or uncatalyzed? __ A. __ B. __ C. __ D. __ E. k Vmax Vo K
∆G‡ 6. Which of the following statements is true for members of a given family of isoenzymes? __ A. __ B. __ C. __ D. __ E. They have the same distribution across all organs and tissues. They have the same quaternary structure. They catalyze the same chemical reactions. Identical isoenzymes exist throughout all stages of development. They respond identically to allosteric regulators. 7. The Hill constant for a protein is 3.7. What can you conclude about its ligand binding? __ A. __ B. __ C. __ D. __ E. It demonstrates negative cooperativity. The curve of fractional saturation versus ligand concentration would be hyperbolic. There must be at least four ligand binding sites in the protein. Without knowing the identity of the ligand, we can conclude nothing about cooperativity. The protein resembles myoglobin in its ligand binding characteristics. 8. Chymotrypsin has a catalytic triad of Asp, His, and Ser residues that are crucial to the catalytic mechanism. The serine hydroxyl functions as a nucleophile. What do the other two amino acids do to support this initial nucleophilic reaction? __ A. __ B. __ C. __ D. __ E. His acts as a general base; Asp, as an electrostatic catalyst. His acts as a general acid; Asp, as an electrostatic catalyst. Both act to bind the substrate, thereby decreasing its entropy. His coordinates the zinc cofactor; Asp acts as a general base. Both act to destabilize the substrate through unfavorable electrostatic forces, thereby making the transition state easier to obtain. 2 9. The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics:
Vo Substrate added (µmol/min) (mmol/L) ————————————————————————————— 217 0.8 325 2 433 4 488 6 647 1,000 ————————————————————————————— The Km for this enzyme is approximately: __ A. __ B. __ C. __ D. __ E. 10. 1 mM. 2 mM. 4 mM. 6 mM. 1,000 mM. Both water and the six-carbon sugar glucose share an —OH that can serve as a substrate for a reaction with the terminal phosphate of ATP catalyzed by the enzyme hexokinase. Glucose, however, is about a million times more reactive as a substrate than water. The best explanation is that: __ A. __ B. __ C. __ D. __ E. glucose has more —OH groups per molecule than water. the larger glucose binds better to the enzyme; furthermore, it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis. water cannot normally reach the hydrophobic active site but glucose can. water and the second substrate, ATP, compete for the active site. The result is competitive inhibition of the enzyme. the —OH group of water is attached to an inhibitory H atom while the glucose —OH group is attached to C. 11. When two carbohydrates are epimers, __ A. __ B. __ C. __ D. __ E. one is a pyranose and the other is a furanose. one is an aldose and the other is a ketose. they differ only in the configuration around one carbon atom. they differ in length by one carbon. they are chemically indistinguishable. 12. Which of the following pairs is interconverted during mutarotation? __ A. __ B. __ C. __ D. __ E. D- glucose and D-fructose D-glucose and D-galactose D-glucose and L-glucose
α−D-glucose and β−D-glucose D-glucose and D-glucosamine 3 A nswer Key
BC 367 Exam 2November 17, 2005 Name____________________ Part I- Multiple Choice (36 points)- Choose the single most correct answer. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. E D C D D C C A B B C D 4 ...
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This note was uploaded on 10/12/2010 for the course BC BC367 taught by Professor Millard during the Spring '10 term at Colby.
- Spring '10