WRITE YOUR NAME AND I.D. NUMBER LEGIBLY ON EVERY PAGE – PAGES WILL BE SEPARATED FOR GRADING! CHECK TO BE SURE YOU HAVE 5 PAGES, NAME (print): ANSWERS INCLUDING COVER PAGE. I swear/affirm that I have neither given nor received any assistance with this exam. Signature: Date: BIOCHEMISTRY 460 THIRD HOUR EXAMINATION FORM A (YELLOW) ANSWERS April 11, 2007 A NON-PROGRAMMABLE CALCULATOR MAY BE USED ON THIS EXAM. No programmable calculators are permitted, and no sharing of calculators. We have a couple of spare calculators to lend in an emergency. SHOW YOUR WORK FOR ALL CALCULATIONS, AND BE SURE TO STATE UNITS OF ANY NUMERICAL ANSWERS. If the reasoning, calculations, or answer are shown anywhere other than in the space provided, make a note in the space provided and put answer on BACK OF SAME PAGE so the grader for that page will have it. USEFUL CONSTANTS: R (gas constant) = 8.315 J•mol–1•Kelvin–1 = 8.315 x 10–3 kJ•mol–1•Kelvin–1 F (Faraday Constant) = 96.48 kJ•V–1•mol–1 If temperature = 25 °C, absolute temperature T = 298 K (Assume this temperature unless problem states otherwise.) Potentially useful equations: Energy Charge (EC): [ATP]+ 0.5[ADP] [ATP]+ [ADP]+ [AMP] Change in Free Energy: ΔG'= ΔGº'+RT ln [product]actual [substrate]actual At equilibrium (when ΔG’ = 0): ΔGº'= −RT ln [product]equilibrium [substrate]equilibrium Change in Reduction Potential: ΔEº'= (Eº'e- acceptor ) − (Eº'e- donor) Relating ΔGº' to ΔEº': ΔGº'= −nFΔEº'Biochemistry 460, Exam #3 Form A ANSWERS NAME April 11, 2007 page 2 1. (6 pts, 2 pts each) Circle T for true statements and F for false statements. T / F Biological systems at equilibrium with the environment are dead. T / F Burning 15.7 g of glucose in a bomb calorimeter releases the same amount of energy as aerobic respiration of 1 gram of glucose in your body. T / F Energy input is required to increase the entropy of a biological system. 2. (4 pts) Name two primary messengers (aside from epinephrine) discussed in class. Any two of the following: Insulin; Glucagon; Epidermal Growth Factor (EGF); Cortisol; NO (Nitric Oxide); Acetylcholine 3. (6 pts) Name 3 types (general classes, not specific examples) of receptor proteins. Any three of the following: G protein coupled receptors (or 7TM receptors or Seven-Transmembrane-Helix Receptors) Receptor Tyrosine Kinases TNF (or Tumor Necrosis Factor) Family Receptors Ion Channel Receptors Intracellular (or Steroid) Receptors 4. (6 pts) Outline the series of events involved in G protein activation, starting with the arrival of a signal at the cell surface and ending with the active component of the G protein that affects its target. Conformational change of receptor protein causes structural change in the G protein – GDP leaves, GTP binds GTP binding causes a structural change in the G protein—molecular switch dimer then dissociates and activated α subunit goes off to affect other proteins 5. (6 pts) Cyclic AMP (cAMP) was discussed in detail in class and in the text. A. (2 pts) The role of cAMP in the epinephrine stimulated signaling pathway is: 1. Receptor 2. Inhibitor of epinephrine signaling 3. Primary messenger 4. Second messenger 5. Energy storage compound 6. Hormone B. (4 pts) Briefly explain what triggers cAMP production in this pathway; how is cAMP made? The epinephrine receptor binds epinephrine and activates a G protein, which stimulates adenylate cyclase. Adenylate cyclase is an enzyme and it converts ATP into cAMP. /28 p. 2 (28 points) p. 3 (21 points) p. 4 (29 points) p. 5 (22 points) TOTAL: (100 points)Biochemistry 460, Exam #3 Form A ANSWERS NAME April 11, 2007 page 3 6. (5 pts) Explain in general terms why anabolism is favored under conditions of high Energy Charge in the cell. (You do NOT need to discuss specific reactions that are regulated.) The ratio of ATP to ADP (or to AMP) is high when the Energy Charge is high, meaning that ATP levels are high. The cell responds by inhibiting ATP production and storing energy in the form of fats or carbohydrates (such as glycogen), which are synthesized by anabolic processes. ATP is used by/required for anabolic processes. 7. (5 pts) Under certain conditions, muscle cells turn on a process that converts sugar into lactate instead of into acetyl-CoA. A. (2 pts) What is this process called? Fermentation B. (3 pts) What conditions are required to make this happen? Anaerobic conditions (O2 is absent or O2 at low levels). OK to say something about high exercise, like sprinting, that depletes O2 from muscle cells. NOT OK to say it is due to aerobic or slow exercise. 8. (7 pts) The enzyme phosphoglycerate kinase catalyzes the 7th step in glycolysis and generates two of the ATP molecules (per glucose molecule) formed by glycolysis. A. (3 pts) Besides ADP and ATP, what are the substrate and product of phosphoglycerate kinase? (Circle the correct answer for each.) Substrate 1. dihydroxyacetone phosphate (DHAP) 2. 3-phosphoglycerate (3-PGA) 3. 1,3-bisphosphoglycerate (1,3-BPG) 4. glyceraldehyde-3-phosphate (GAP) 5. fructose-1,6-bisphosphate (F-1,6-BP) 6. phosphoenolypyruvate (PEP) 7. pyruvate Product 1. dihydroxyacetone phosphate (DHAP) 2. 3-phosphoglycerate (3-PGA) 3. 1,3-bisphosphoglycerate (1,3-BPG) 4. glyceraldehyde-3-phosphate (GAP) 5. fructose-1,6-bisphosphate (F-1,6-BP) 6. phosphoenolypyruvate (PEP) 7. pyruvate B. (4 pts) The ΔG°' of this reaction in glycolysis is −18.8 kJ·mol-1, but the ΔG' under physiological conditions is +1.3 kJ·mol-1. Why is this reaction able to proceed forward, given the actual ΔG' in the cell? The overall net ΔG' of glycolysis is a large negative number, and is very favorable. This reaction is not occurring in isolation; it is able to proceed to the right despite having an actual ΔG' > 0 because it is coupled in the glycolytic pathway to all the other 9 reactions in the pathway, including more favorable reactions that have large negative ΔG' values, so the sum of all the actual ΔG' values for the forward direction of the pathway is highly favorable (<< 0). 9. (4 pts) The disease beriberi is caused by a nutritional deficiency in vitamin B1 (thiamine). What key mitochondrial enzyme that is required for the production of acetyl-CoA from glucose
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