Name: __________________________________ NetID:_________________________ 1 MCB 450 Exam II March 12, 2015 Form A Choose the BEST answer from the available choices. Only non-graphing calculators are permitted for use on this exam. Information you may need: R = 8.315 J mol-1 K-1; ln # = 2.3 log10#; K = °C + 273 Part I: 24 Multiple-Choice questions. Each question is worth 4 points. (total of 96 possible points). Record all of your answers on the provided scantron sheet. 1. The notation 18:3 indicates which of the following about a fatty acid? a. The acyl chain contains 18 carbons, and a single C=C bond that is three bonds in from the omega carbon. b. There is one double bond between carbons 3 and 4 in the acyl chain. c. There are 15 trans double bonds in this 18 carbon fatty acid. d. It is a molecule with three 18 carbon acyl chains ester-linked to glycerol. e. There are 18 carbons in the chain and there are three double bonds. 2. Which of the following components of the plasma membranes of mammalian cells has a polar headgroup with a net negative charge at physiological pH? a. Phosphatidylserine b. Sphingomyelin c. Phosphatidylcholine d. Phosphatidylethanolamine e. CholesterolName: __________________________________ NetID:_________________________ 2 3. Which of structures A-K correspond to the following: 1. The membrane anchor of a farnesylated protein 2. Sphingomyelin 3. Testosterone 4. cis-delta9-octadecenoate a. 1 = G; 2 = F; 3 = J; 4 = E b. 1 = J; 2 = B; 3 = D; 4 = A c. 1 = B; 2 = J; 3 = A; 4 = G d. 1 = C; 2 = H; 3 = K; 4 = I e. 1 = D; 2 = C; 3 = H; 4 = K _ + CH3 H3C CH3 N CH2 CH2 + CH3 H3C CH3 N CH2 CH2 _ + _ A B I C D E F G H J KName: __________________________________ NetID:_________________________ 3 4. Which of the following statements applies to mammalian cell membranes? a. Phospholipids, glycolipids, and proteins readily undergo transverse (“flip-flop”) diffusion from one side of the membrane to the other. b. Individual lipid molecules are free to diffuse laterally in one surface of the bilayer. c. The polar headgroups of phospholipids, glycolipids, and cholesterol face towards the interior of the bilayer. d. Polar, but uncharged compounds readily diffuse across these bilayers. e. Each leaflet of the bilayer is stabilized by amide linkages between the headgroups of phosphatidylethanolamine and phosphatidylserine. 5. Which one of these statements about the potassium channel is NOT true? a. It has a water-filled pore that extends in from the cytoplasmic face of the cell membrane that allows hydrated K+ ions to pass two thirds of the way through the membrane. b. Ejection of K+ on the exterior face of the membrane results from charge repulsion between desolvated K+ ions bound at adjacent sites in the pore. c. Desolvated K+ ions interact with carbonyl groups of the backbone of the peptide strands that are directed into the narrow part of the channel. d. Na+ ions are too small to make the complete set of interactions with carbonyl groups in the pore, so they remain mostly solvated. e. K+ ions that retain their hydration shells pass through the pore from a region of high concentration to one of low concentration, whereas Na+ ions are desolvated and selectively retained in the pore. 6. The hydrolysis of ATP by the Na+-K+ ATPase provides the energy needed for which of the following: a. Symport of three Na+ ions and two K+ ions into the cell. b. Transport of three K+ ions out of the cell and two Na+ ions into the cell. c. Transport of three Na+ ions out of the cell and two K+ ions into the cell. d. Transport of three K+ ions into the cell and two Na+ ions out of the cell. e. Transport of three Na+ ions into the cell and two K+ ions out of the cell.Name: __________________________________ NetID:_________________________ 4 7. Which of the following biochemical reactions is an example of… 1. An oxidoreductase 2. A lyase a. 1 = B; 2 = E b. 1 = C; 2 = D c. 1 = G; 2 = A d. 1 = F; 2 = B e. 1 = E; 2 = C F G + C E 4. B A DName: __________________________________ NetID:_________________________ 5 8. For an enzyme-catalyzed reaction that can be written as below, Km can be considered a measure of the affinity of an enzyme for its substrate providing: a. k2 >> k-1 b. k2= k1 c. k2 << k-1 d. k1 >> k2 e. k1 = k-1 9. Which of the following statements about enzymes is NOT true? a. Their activity depends on the integrity of their native conformation. b. They are complementary to their substrate’s transition state. c. They increase the activation energy of a biochemical reaction. d. They may require metal ions for activity. e. They can undergo a conformational change when they bind their substrate. 10. Which of the following statements about biochemical reactions is NOT true? a. The Keq of a reaction is directly related to the reaction’s ∆G°. b. If initial [reactants] << [products], their actual ∆G in cells can be negative even if ∆G°’ is positive. c. Enzymes affect the rate of the reaction they catalyze, but not the equilibrium of the reaction. d. The conversion reactants to products may not proceed even if ∆G is favorable. e. When ∆G°’ is negative, products contain less free energy than reactants, and the reaction will proceed spontaneously under biochemical standard conditions. E + S ES E + P K1 K2 k-1Name: __________________________________ NetID:_________________________ 6 11. During an enzyme-catalyzed reaction, whose progress is shown in this diagram, a thermodynamic “pit” (arrowed) would occur when: a. ES forms faster than it dissociates. b. S is not bound tightly to the enzyme. c. ES is highly stable. d. S is positioned incorrectly in the active site of the enzyme. e. ES is not very stable. 12. An enzyme-catalyzed reaction was carried out with the substrate concentration initially a 250 times greater than the Km for that substrate. After 8 minutes, 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 15 µmol. If, in a separate experiment, one-quarter as much enzyme and twice as much substrate had been combined, how long would it take for the same amount (15 µmol) of product to be formed? a. 32 min b. 16 min c. 8 min d. 4 min e. 2 minName: __________________________________
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