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UIUC MCB 450 - Sample Exam 2 Sp15 - Ans

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NAME:______________________________ NETWORK ID:___________________ !!!!!!!!!!!!!!!MCB!450!Sample!Exam!II!!Choose!the!BEST!answer!from!the!available!choices.!Only!nonAgraphing!calculators!are!permitted!for!use!on!this!exam.!!Section!1!MultipleAchoice!Questions.!!Each!question!is!worth!6!points.!!1. A 2 micromolar solution of cytidine deaminase catalyzes the formation of 0.6 mmoles uridine s-1 when saturated with cytidine. What is cytidine deaminase’s kcat? (A) 300 s-1 (B) 300,000 s-1 (C) 300 M-1 s-1 (D) 300 mM (E) 3.33 msec 2. The enzyme invertase follows Michaelis-Menten kinetics. A 9 micromolar solution of invertase has a kcat of 2167 s-1 when converting sucrose to fructose and glucose. What is invertase’s Vmax with sucrose? a. 4.15 mmoles s-1 b. 4.15 M-1 s-1. c. 2.4 x 106 M-1 s-1 d. 241 msec. e. 19.5 mmoles s-1NAME:______________________________ NETWORK ID:___________________ !!!2!3. For a one-substrate, enzyme-catalyzed reaction, double-reciprocal plots were determined for three different enzyme concentrations. Line one representing the lowest enzyme concentration, whereas line three represents the highest enzyme concentration. Which of the following three families of curve would you expect to be obtained? ANS is c 4. The enzyme fructose 1,6-bisphosphate aldolase (“aldolase”) catalyzes the reaction: Fructose 1,6-bisphosphate dihydroxyacetone phosphate + glyceraldehyde-3- phosphate. The ∆G°’ for this reaction is +23.8 kJ/mol. The concentration of fructose 1,6-bisphosphate bisphosphate in liver cells was determined to be 1.4 x 10-5 M, that of dihydroxyacetone phosphate, 1.6 x 10-5 M, and that of glyceraldehyde-3-phosphate, 3.0 x 10-6 M. What is the actual free energy change (∆G’) for the aldolase reaction in liver cells at body temperature (37°C)? a. + 8.7 kJ/mol b. - 7.4 kJ/mol c. - 11.9 kJ/mol d. - 8.7 kJ/mol e. + 7.4 kJ/molNAME:______________________________ NETWORK ID:___________________ !!!3!5. The following panels represent 6 different steps during chymotrypsin: reaction. Which of the following choices lists the steps in chronological order (first to last)? a. B, F, D, A, C, E b. D, A, B, F, C, E c. D, F, B, C, A, E d. A, C, E, D, B, F e. E, A, C, D, B, F 6. Which of the above chymotrypsin steps (see diagrams in question 4) correspond to a general acid catalytic step: a. A and B b. A and C c. B and F d. C and F e. B and DNAME:______________________________ NETWORK ID:___________________ !!!4!Section!2!MultipleAchoice!Questions.!!Each!question!is!worth!4!points.!!7. Which of these is a general feature of the bilayer membranes? a. The polar head groups face inward toward the inside of the bilayer. b. Individual lipid molecules are free to diffuse laterally in one surface of the bilayer. c. Both proteins and lipids readily undergo transverse (“flip-flop”) diffusion from the inside to the outside of the membrane. d. Membrane proteins adopt an extended conformation between the fatty acyl chains of the two leaflets of the bilayer. e. Ions and charged compounds readily diffuse across the bilayer. 8. Which of the following membranes would be most fluid? a. One containing lipids with exclusively cis,cis-∆9,∆12-octadecadienoate chains b. One containing lipids with exclusively n-hexadecanoate chains. c. One containing lipids with exclusively n-octadecanoate chains. d. One containing lipids with exclusively cis,cis-∆9,∆12-hexadecadienoate chains. e. They will all have the same fluidity. 9. Proteins can associate with bilayer membranes via a. thioether-linked 15- or 20 carbon isoprenoid groups. b. electrostatic interactions that can be broken by changing ionic strength or pH. c. one or more alpha helices around 20 amino acids in length. d. a C14:0 fatty acid amide-linked to an amino terminal amino acid. e. All of the above options are correct.NAME:______________________________ NETWORK ID:___________________ !!!5!10. Which one of these statements about the Michaelis constant, Km, is TRUE? a. It can be determined from the 1/V0 intercept of a plot of 1/V0 versus 1/[S]. b. It is equal to the substrate concentration at which all the active sites in the population of enzyme molecules are filled. c. It is the compilation of three rate constants: (k1 + k-2) / k-1. d. The lower an enzyme’s Km, the faster it reacts with its substrate. e. None of the above statements are true. 11. 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. The Michaelis-Menten constant Km equals the [S] at which V = 1/2 Vmax. c. If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor. d. The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is shifted in favor of product formation. e. The rate of a reaction decreases steadily with time as the substrate is depleted. 12. Given are five KM values for the binding of substrates to a particular enzyme. Which has the strongest affinity when k−1 is greater than k2? a. 150 mM b. 0.15 mM c. 150 mM d. 1.5 nM e. 15,000 x 10-12 MNAME:______________________________ NETWORK ID:___________________ !!!6!13. Enzymes K and M have the same specificity constant. Which one of the following statements about K and M is TRUE? a. They must have the same Vmax. b. Their kcats must be the same, but the substrate concentration at which their V0 is half Vmax can be different. c. Their kcats and Kms can be different but their kcat/Km ratios must be the same. d. In a given unit of time, single molecules of K and M both convert the same number of substrate molecules to product when saturated with substrate, providing the same substrate is used. e. Their kcats are different but their Kms must be the same. 14. Double reciprocal plots A, B, and C (below) are characteristic of the three types of reversible inhibition described in class. Which double reciprocal plot shows uncompetitive inhibition, and which of schemes 1-5 describes uncompetitive inhibition? a. Plot C and scheme 2 b. Plot A and scheme 4 c. Plot B and scheme 4 d. Plot C and scheme 1 e. Plot B and scheme 3NAME:______________________________


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