BCH 4054 HOUR TEST 1 NAME _____________________ September 22, 1995 Selected Free Energies of Hydrolysis Compound delta Go' (kJ/mol) Phosphoenolpyruvate -62 Acetyl phosphate -43 Creatine phosphate -43 Pyrophosphate -33 ATP (to ADP) -30 Glucose-1-phosphate -21 Glucose-6-phosphate -14 Glycerol-3-phosphate - 9 Selected Standard Reduction Potentials Reduction Half Reaction Eo' (V) Ferredoxin(Fe3+) + e- -----> Ferredoxin(Fe2+) -0.43 2 H+ + 2 e- -----> H2 -0.42 NAD+ + H+ + 2 e- -----> NADH -0.32 FAD + 2 H+ + 2 e- -----> FADH2 -0.22 Acetaldehyde + 2 H+ + 2 e- -----> Ethanol -0.20 Pyruvate + 2 H+ + 2 e- -----> Lactate -0.18 Oxaloacetate + 2 H+ + 2 e- -----> Malate -0.17 Fumarate + 2 H+ + 2 e- -----> Succinate +0.03 CoQ + 2 H+ + 2 e- -----> CoQH2 +0.04 Cyt b(ox) + e- -----> Cyt b(red) +0.08 Cyt c1(ox) + e- -----> Cyt c1(red) +0.22 Cyt c(ox) + e- -----> Cyt c(red) +0.23 Cyt a(ox) + e- -----> Cyt a(red) +0.29 Cyt f(ox) + e- -----> Cyt f(red) +0.36 1/2 O2 + 2 H+ + 2 e- -----> H20 +0.82 Use the following constants: R = 8.3 x 10-3 kJ mol-1 K-1; T = 310 K; ln x = 2.3 log x F = 96.5 kJV-1mol-1 Points 1. The following reaction occurs during mitochondrial electron transport: CoQH2 + 2 cyt c(ox) -----> CoQ + 2 cyt c(red) (4) (a) Which complex catalyzes this reaction, and what components does it contain? (4) (b) Calculate delta Go' for this reaction. (4) (c) Assuming this complex pumps 2 protons, what proton motive force (delta p) could be produced if the CoQH2/CoQ and cyt c(red)/cyt c(ox) ratios were maintained at 1? (4) (d) Assuming that the 0.15 volts of the delta p is from an electrical potential, delta psi, what would be the delta pH across the inner mitochondrial membrane? 2. A similar transport of electrons from a quinone to a peripheral membrane protein occurs in photosynthesis. (2) (a) Identify the quinone and peripheral membrane protein. (3) (b) The proton gradient in this case produces no delta psi. Why? (4) (c) Assuming delta p to be similar to that calculated in question 1(c) above, what would the delta pH be in this case? (10) 3. Functional electron-transport systems can be reconstituted from purified respiratory electron-transport chain components and membrane vesicles. For vesicles containing each of the following sets of components, determine the final electron acceptor. Assume O2 is present and that the components are properly oriented in the vesicles. (a) NADH, Q, Complexes I, III, and IV (b) NADH, Q, cytochrome c, Complexes II and III (c) Succinate, Q, cytochrome c, Complexes II, III, and IV (d) Succinate, Q, cytochrome c, Complexes II and III (e) Succinate, Q, Complexes I and III (12) 4. Identify which of the respiratory complexes I, II, III, or IV fit the following descriptions (more than one may apply). ______ contains cytochromes ______ contains Cu ______ contains Fe/S proteins ______ reduces CoQ ______ acts as a proton pump ______ interacts with cyt c (4) 5. Antimycin blocks electron transport by binding to complex III. When antimycin is added to mitochondria in the presence of both an oxidizable substrate (pyruvate, for example) and oxygen, predict whether the following would increase or decrease. _________ NADH/NAD+ ratio _________ CoQ/CoQH2 ratio _________ cyt c(red)/cyt c (ox) ratio _________ succinate/fumarate ratio (8) 6. Both cyanide and oligomycin when added to mitochondria will block oxygen consumption. (a) Explain where each inhibits. (b) What would be the effect of adding dinitrophenol to each of the inhibited reactions? (12) 7. In the Z scheme for the light reaction of photosynthesis two pigment systems are responsible for the transfer of electrons from water (forming oxygen) to NADP+ (forming NADPH). Outline the scheme, placing the following components in their proper location along the path of the electrons: plastoquinone, plastocyanin, manganese, ferredoxin, cytochrome b/f complex, P700, P680, pheophytin. (6) 8. Match a component in the list at the right with each statement below by placing the appropriate letter in the blank. ___ reduced directly by P680*. a. pheophytin a b. plastocyanin ___ oxidized directly by P680+. c. phycocyanin d. a tyrosine residue ___ oxidized directly by P700+. e. Ao, a chlorophyll a ___ reduced directly by P700*. ___ an accessory pigment. ___ chlorophyll a without Mg2+. (3) 9. The overall dark reaction requires 3 ATP and 2 NADPH for each CO2 converted to carbohydrate, while passage of 2 electrons from H2O to NADPH via the "Z" scheme yields only about 1 ATP per NADPH generated. How is the additional ATP generated? 10. RuBisCO catalyzes the reaction of ribulose-1,5-bisphosphate with O2 as well as with CO2. (8) (a) Write the equation for these reactions, including the structure of reactants and products. (3) (b) Explain what effect Mg2+, pH, and CO2 (other than as a substrate) have on the activity of RuBisCO, and how these effects link RuBisCO activity to the light reaction. 11. Some plants contain an additional mechanism for "fixing" CO2, known as the C4 pathway. (6) (a) Give the structure of the reactants and products, and the name of the enzyme, for the reaction by which CO2 is fixed. (3) (b) The C4 pathway requires more energy from ATP per CO2 ultimately incorporated into carbohydrate. What advantage does it give the cell in return?