BCMB 3100 Fall 2013 Exam III

Transcription

1 BCMB 3100 Fall 2013 Exam III 1. (10 pts.) (a.) Briefly describe the purpose of the glycerol dehydrogenase phosphate shuttle. (b.) How many ATPs can be made when electrons enter the electron transport chain via this shuttle? Explain your answer. (a.) The purpose of the glycerol phosphate dehydrogenase shuttle is to pass electrons from cytosolic NADH (produced by glycolysis) into the mitochondrial electron transport system. This is done via FAD to FADH 2 and from FADH 2 to Q. (b.) Since the electrons enter at Q and into complex III, by-passing complex I, there is a net transfer of six protons across the membrane and since 4 protons are required to synthesize and transport one ATP there would be 6/4 or 1.5 ATP molecules per NADH entering via this shuttle. 2. (8 pts; 4 for part (a) and 4 for part (b)) Peter Mitchell formulated the chemiosmotic theory based on an experiment in which he measured the consumption of oxygen by mitochondria in the presence of NADH (substrate) and the addition of ADP, or 2,4-dinitrophenol; the results are shown below. Briefly state (a.) the chemiosmotic theory, and (b.) how the results of this experiment supports this theory. (a.) The chemiosmotic theory proposed that the mitochondrial enzyme complex generates a proton gradient across the membrane which provides energy for ADP phosphorylation. (b.) First, the substrate (e.g. NADH) in the presence of mitochondria and with the addition of ADP stimulate the consumption of O 2 until the ADP is all utilized. However when uncouplers, such as 2,4-dinitrophenol, are membrane-soluble compounds which allow the unrestricted transfer of protons across the mitochondrial membrane, thereby destroying the proton gradient. Thus, it was concluded that a proton gradient is required, i.e. coupled, for the conversion of ADP to ATP.

2 3. (10 pts.) If actively respiring mitochondria are exposed to an inhibitor of ATP synthase, the electron transport chain ceases to operate. Why? The proton gradient cannot be dissipated by flow through ATP synthase. It becomes large enough that the energy released by the ETC is insufficient to pump protons across the membrane and electron transport ceases. 4. (12 pts.; 8pts. for part a and 4 pts. for part b.) (a.) On the diagram below place the following components of photosynthetic transport in their correct location. A. Ferridoxin-NADP + reductase B. P700 C. OEC or Mn center D. P700* E. P680 F. Plastocyanin (Pc) G. P680* H. Cytochrome bf G Cyclic electron transport D A (b.) On the diagram show what happens during cyclic electron transport, and give the purpose of cyclic electron transport. Cyclic electron transport occurs at high NADPH/NADP + ratios where there is insufficient NADP + to accept the electrons. 5. (10 pts; 8 for (a) and 2 for (b)) (a.) Calculate the E o and G o for the reduction of NADP + by ferridoxin; i.e. for the reaction: (Faraday s Const. = 96.5 kj/mol/v) NADP + + Fd red NADPH + Fd ox G o = -zf E o E o = (-0.43) = 0.11V G o = (96.48kJ/mole/V)(0.11V) = 1.2kJ/mole (b.) Why does ferridoxin-nadp + oxidoreductase have FAD as a co-factor? FAD is necessary to accept electrons one at a time from the oxidoreductase and deliver them two at a time to NADP + to give NADPH. C E H F B

3 6. (10 pts; 6 pts for (a.) and 4 pts for (b.)) (a.) Describe the stages of the Calvin cycle and the purpose of each stage. (b.) Draw the reaction (structures of reactants and products) of the RUBISCO reaction for the Calvin cycle. (a.) Oxidation: Combines CO 2 with ribulose-1,5-bisphosphate to make 3-phosphoglycerate. Reduction: Conversion of 3-phosphglycerate to glyceraldehyde-3-phosphate which is used for glucose synthesis and for synthesis of more ribulose-1,5-bisphosphate. Regeneration: The regeneration of ribulose-1,5-bisphosphate from glyceraldehyde-3- phosphate. (b.) O H OH + CO 2 H OH H OH COOH 7. (10 pts.) Use the following molecules to draw the structure of a phospholipid: Glycerol, serine, tetradecanoic acid, and C18:1 11 (place tetradecanonic acid at C1 and C18:1 11 at C2 of the phospholipid). 8. (10 pts.) Match the following with regard to transport and signal transduction mechanisms: A. Active Transport H down a concentration gradient B. camp D two molecules in samedirection C. Uniport I transducer D. Symport C one molecule in one direction E. Vesicle A saturable and requires energy F. Protein kinase E endocytosis G. Antiport B second messenger H. Passive transport J effector enzyme I. G-protein G two molecules in opposite directions J. Adenylate cyclase F cytoplasmic factor

4 9. (8 pts.) Place the following list of reactions or relevant locations in the b oxidation of fatty acids in the proper order. (Problem Chapter 27) (a) Reaction with carnitine. (b) Fatty acid in the cytoplasm. (c) Activation of fatty acid by joining to CoA. (d) Hydration. (e) NAD + -linked oxidation. (f) Thiolysis. (g) Acyl CoA in mitochondrion. (h) FAD-linked oxidation. b, c, a, g, h, d, e, f 10. (12 pts; 7 for part (a.) and 5 for part (b.) (a.) Match the following with regard to the synthesis of fatty acids. A. Enoyl reductase B. Malonyl transacylase C. -Ketoacyl synthase D. Acetyl carboxylase E. 3-Hydroxy dehydratase F. Acetyl transacylase G. -Ketoacyl reductase (b.). Briefly describe how fatty acid synthesis is regulated by AMP-dependent protein kinase (AMPK). AMPK is activated by AMP. AMPK phosphorylates and inactivates acetyl carboxylase, the first enzyme in fatty acid synthesis, thereby inhibiting fatty acid synthesis.

5 EXTRA CREDIT POINTs (15 pts.) TRUE/FALSE. Write T if the statement is true and F if the statement is false. T 1) Lipids derived from cholesterol aid digestion and absorption of other lipids such as triacylglycerols. T 2) Vitamins A, E and K are all isoprenoids. F 3) Transport of ions and small molecules through a bacterial membrane pore requires energy from an ATP to ADP conversion. T 4) The principle advantage of a cascade mechanism in signal transduction is that one molecule of a ligand can affect many intracellular proteins without crossing the plasma membrane. T 5) A biotin-dependent enzyme is responsible for catalyzing the carboxylation of acetyl CoA. F 6) In mammals the oxidation of fatty acids produces a two-carbon product and the synthesis of fatty acids begins with a two-carbon substrate. T 7) During starvation ketone bodies can take the place of glucose as a fuel for brain cells. T 8) Snake venom can cause the lysis of red blood cells due to the presence of phospholipase A2. T 9) Most of the free energy needed to drive ATP formation in the mitochondria is the result of an electrical contribution from a charge gradient across the inner mitochondrial membrane. T 10) Complex II participates in both the electron transport chain and the citric acid cycle. T 11) Mitochondrial electron transport and ATP formation are interdependent. F 12) The light reactions of photosynthesis form carbohydrates from ATP, NADPH, H + and CO 2. T 13) Rubisco often makes up to 50% of the soluble protein in plant leaves. F 14) Most plants contain a rubisco enzyme that catalyzes only a carboxylation reaction in the fixation of carbon dioxide. F 15) The CAM pathway and the Calvin cycle generally occur simultaneously in plants during the daytime.