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Sample questions for exam 3 Part 1 1. The role of the UDP group in UDP-glucose is to activate the carbon of glucose. a. 1 b. 2 c. 3 d. 4 e. 6 2. The energy for the synthesis of ATP by the mitochondrial ATP synthase comes from the movement of through the enzyme. a. electrons b. coenzyme Q c. protons d. NADH 3. During the Krebs cycle, GTP is synthesized in a reaction in which is converted to a. oxaloacetate; citrate b. citrate; isocitrate c. succinyl-coa; succinate d. succinate; fumarate 4. When electrons of NADH are transported from the cytoplasm to mitochondria via the malate-aspartate shuttle, reduced NADH is formed in the mitochondria; when
they are transported via the glycerol-phosphate shuttle, reduced is formed in the mitochondria. a. ATP b. FMN c. NADP d. FAD 5. Carbamoyl phosphate is a precursor for the biosynthesis of a. urea b. citrate c. glucose d. all of the above 6. The first enzyme in the pathway for pyrimidine biosynthesis is allosterically inhibited by a. ATP b. CTP c. GTP d. all of the above 7. The free energy contained in a proton gradient consists of two components, potential and potential. a. proton; electron b. enthalpy; entropy c. chemical; electrical
d. oxidation; reduction 8. The substrates for glycogen synthase are a growing glycogen chain and a. glucose b. glucose 6 phosphate c. glucose 1 phosphate d. fructose 6 phosphate 9. ACP (Acyl Carrier Protein) of the fatty acid synthase complex has a prosthetic group which structurally resembles a. heme b. coenzyme A c. lipoic acid d. NADP 10. An example of an enzyme that is involved in the biosynthesis of DNA precursors but not RNA precursors is a. ribonucleotide reductase b. transaminase c. carbomoylphosphate synthetase d. all of the above Part 2 Question 1
Alanine was synthesized with 15 N in the α-amino group. An experiment was carried out in which this [ 15 N]-labeled alanine was added to cells; there was found to be a rapid production of 15 NH 3. Suggest a metabolic pathway (using only reactions which are known to exist) that would lead to this result. (You must show the structures of the metabolites in the pathway, but only the names of cofactors.) Question 2 a) How many ATPs (net) are produced from the complete aerobic metabolic conversion of stearic acid (saturated C18 fatty acid) to CO 2? You must explain how you got the answer in order to get credit. (You do not have to show the actual reactions.) b) How many ATPs (net) are utilized for the biosynthesis of stearic acid from acetylcoa? You must explain how you got the answer in order to get credit. (You do not have to show the actual reactions.) Question 3 Choose 2 reactions of gluconeogenesis which are different from the reversal of the reactions of glycolysis. For each, show the reaction of gluconeogenesis and the corresponding reverse reaction of glycolysis. (For all reactions show the structures of the reactants and products, but only the names of the cofactors.) Question 4 A recently discovered bacterium carries out ATP synthesis coupled to the flow of electrons through a chain of carriers to a final electron acceptor. The components of its electron transfer chain differ from those found in mitochondria; they are listed below (in alphabetical order) with their standard reduction potentials. Carrier Oxidized form Reduced form Electrons E o ' (V) name transferred Fe-S1 Fe-S protein1 (ox) Fe-S protein1 (red) 2 +0.22 Fe-S2 Fe-S protein2 (ox) Fe-S protein2 (red) 2 +0.89 FPa flavoprotein a (ox) flavoprotein a (red) 2 +0.77 FPb flavoprotein b (ox) flavoprotein b (red) 2 0.62 NAD NAD+ NADH 2 0.32 a) Place the electron carriers in the order in which they are most likely to act in carrying electrons. (Fill in the blanks below with the carrier names)
b) Is it likely that O 2 (for which E o ' = + 0.82 V) is the final electron acceptor in this organism? Explain why or why not? c) Calculate the maximum number of ATP molecules that could theoretically be synthesized, under standard conditions, per pair of electrons transferred through this chain of carriers. [Note: The Faraday constant, F = 96.48 kj/v-mol. and for ATP synthesis ΔG ' = +30.5 kj/mol] You must show how you got the answer in order to get credit. Question 5 You are shown the structures of 4 molecules which are intermediates in metabolic pathways we have studied. You should be able togive the name of each molecule and the name of its immediate metabolic precursor (i.e. the substrate of the reaction in which it is formed). Examples of structures from last year: PRPP, urea, dutp, fumarate
Answers Part 1 1. a 2. c 3. c 4. d 5. a 6. b 7. c 8. e 9. b 10. a Part 2 1) 2 reactions. a) transamination of the N-15 to α-ketoglutarate to form glutamate. (see Page 616). b) oxidative deamination of glutamate to form N-15 ammonia.(see Page 619). 2) a) The stearic acid is converted to stearyl-coa. Then 8 rounds of beta oxidation yield 9 molecules of acetyl coa which enter the Krebs cycle. There are 3 parts: 1) 2 ATPs used to convert stearic acid to stearyl-coa. 2) Each round of beta oxidation produces 1 NADH and 1 FADH2 for 5 ATPs. So for 8 rounds: 40 ATP. 3). Each acetyl coa in Krebs cycle gives 3 NADH and 1 FADH2 and 1 GTP for total 12 ATP. So 9 acetyl coas yield 108 ATPs. TOTAL = 45 + 108-2 =146. b) Synthesis requires 1 acetyl coa and 8 malonyl coa. The synthesis of each malonyl coa takes 1 ATP. So total of 8 is used. 3) see pg. 453 4) a) FPb - NAD - FeS1 - FPa - FeS2 b) Not likely because O 2 has a less positive E o than FeS2. c) Δ E o = E o for FeS2 minus E o for FPb =.89 - (-.62) = 1.51; Δ G o = -n F (Δ E o ) = -(2)(96.48)(1.51) = -291 # ATPs = 291/30.5 = 9.5
5) PRPP; Precursor: ribose - 5 - phosphate urea; Precursor: arginine (urea cycle) dudp; Precursor: UDP (ribonucleotide reductase) fumarate; Precursor: succinate (Krebs cycle)