Midterm Еxam II Biochemistry II Answer Key

MIDTERМ ЕХАМ II Biochemistry II I. _______ /42 II. _______/181 III, ______ /20 TOTAL /80 I. MULTIPLE CHOICE (42 points; 3 pts #1-10 and 2 pts #11-16) Choose the best answer as requested in each question Ьу circling the approporitate letter(s). 1. Which of the following conversions requires more than one step? А. в. с. D. Е. 2. alanine 2. glutamate �a-ketoglutarate 3. aspartate _. oxaloacetate 4. proline _. glutamate 5. phenylalanine _. succinate 1, 2, and 4 1, 3' and 5 2' 4' and 5 1 and 4 4 and 5 А new compound is isolated from mitochondria and а claim is made that 18/5 it represents а previously unrecognized carrier in the electron transfer chain, and it is given the name coenzyme z. Which line of evidence do you feel is the least conclusive in assigning this compound а position in the electron transfer chain? А. в. с. D. 3. -+ pyruvate 1. 17/8 When added to а mitochondrial suspension, coenzyme Z very rapidly and specifically is taken up Ьу the mitochondria. Removal of coenzyme z from the mitochondria results in а decreased rate of oxygen consumption. Alternate oxidation and reduction of the mitochondrion-bound coenzyme z can Ье readily demonstrated. The rate of oxidation and reduction of mitochondrion-bound coenzyme is of the same order of magnitude as the overall rate of electron transfer in mitochondria as measured Ьу oxygen consumption. Which of the following statements is false in reference to the mammalian synthesis of urea? А. В. с. D. Krebs was а major contributor to the elucidation of the pathway involved. The precursor to one of the nitrogens of urea is aspartate. The process of urea production is an energy-yielding series of reactions. The amino acid arginine is the immediate precursor to urea. Page 1 17/17 4. In the light-independent ( "dark") reactions of photosynthesis, the Ьiosynthesis of 1 mole of hexose from 6 moles of carbon dioxide requires: А, в. с. D. Е. 5. в. С. D. Е. 18 12 18 12 of moles moles moles moles АТР. of of of of АТР. АТР. АТР, АТР. Which of these amino acids is (are) both ketogenic and glucogenic? А. в. с. D. Е. в. с. D. Е. 1 and 2 and 2 , 3, 1, 3, 2 , 4, 5 4 and 4 and 5 and 5 со 2 in the first reaction of carbon в. с. D. Е. 17/23 19/21 ribose-1,5-Ьisphosphate. ribulose-1,5-Ьisphosphate. ribulose-5-phosphate. 3-phosphoglycerate. ruЬisco. Which of the following statements about the light reactions in photosynthetic plants is false? А. 16/1 isoleucine valine histidine arginine tyrosine The compound that condenses with dioxide fixation is: А. 8. of NADPH and of NADPH and of NADPH and of NADPH and and 1 2 moles bound to hemogloЬin. present at levels that are independent of epinephrine. carried Ьу the protein serum albumin. freely soluЫe in the aqueous phase of the Ыооd. nonexistent; the Ыооd does not contain free fatty acids. 1. 2. 3. 4. 5. 7. moles moles moles moles NADPH Free fatty acids in the Ыoodstream are: А. 6. 18 18 12 12 no 19/18 There are two distinct photosystems, linked together Ьу an electron transfer chain. А membrane-bound ATPase couples АТР synthesis to electron transfer. The ultimate source of electrons for the process is Н 2 О, The ultimate electron acceptor is 0 2 , No со 2 is fixed in the light reactions. Page 2 18/17 9. Which of the following statements about the chemiosmotic theory is correct? А. в. с. D. Е. 10. в. с. D. Е. 11. в. с. D. в. С. D. Е. 13. с. D. Е. 17/24 decarboxylation requiring thiamine pyrophosphate. reduction requiring pyridoxal phosphate. transamination requiring pyridoxal phosphate. hydroxylation requiring NADPH and 02 • oxidative deamination requiring NAD+. The role of hormone-sensitive triacylglycerol lipase is to: А. в. 18/7 cytochrome с is а 2-electron acceptor, whereas CoQH2 is а 1electron donor. cytochrome с is а 1-electron acceptor, whereas CoQHz is а 2electron donor. two molecules of cytochrome с must first combine physically before they are catalytically active. heart muscle has а high rate of oxidative metabolism, and therefore requires twice as much cytochrome с as CoQHz for electron transfer to proceed normally. In amino acid catabolism, the first reaction for many amino acids is a(n): А. 17/4 methylation. acetylation. reduction. desulfuration. transamination. In the reoxidation of CoQHz Ьу purified ubiquinone-cytochrome с reductase (Complex III), the overall stoichiometry of the reaction requires 2 moles of cytochrome с per mole of CoQHz because: А. 12. Electron transfer in mitochondria is accompanied Ьу an asymmetric release of protons on опе side of the inner mitochondrial membrane. The effect of uncoupling reagents is а consequence of their ability to carry electrons through membranes. Although the energy transductions in mitochondria and in chloroplasts are superficially similar, they have fundamentally different mechanisms. The membrane ATPase, which plays an important role in other hypotheses for energy coupling, has no significant role in the chemiosmotic theory. All of the above statements are correct. Pyridoxal phosphate is а cofactor in this class of reactions: А. 18/14 hydrolyze lipids stored in the liver. hydrolyze triacylglycerols stored in adipose tissue. hydrolyze membrane phospholipids in hormone-producing cells. synthesize triacylglycerols in the liver. synthesize lipids in adipose tissue. Page 3 16/3 14. If а person's urine contains unusually high concentrations of urea, which of the following diets has he or she рrоЬаЫу been eating recently? А. в. С. D. 15. high carbohydrate, very low protein low carbohydrate, very high protein high fat, very low protein high fat, high carbohydrate, no protein А fatty acid with an odd number of carbons will enter the citric acid cycle as acetyl-CoA and: А. в. С. D. Е. 16. very very very very в. с. D. Е. II. 16/21 a-ketoglutarate. malate. succinyl-CoA. citrate. butyrate. Antimycin А Ыocks electron transfer between cytochromes Ь and с1, If intact mitochondria were incubated with antimycin А, excess NADH, and an adequate supply of о 2 , which of the following would Ье found in the oxidized state? А. 17/16 18/6 cytochrome а3 cytochrome f cytochrome ь cytochrome е coenzyme Q SHORT ANSWER & PROBLEMS. (18 points) 17. Ala, Cys, Gly, Ser, and Thr are amino acids whose degradation yields pyruvate. Which, if any, of the remaining 15 amino acids also do so? Explain. [NOTE: the pathway for Thr was not covered in class] ( 2 pts) 18. There are 3 steps of branched-chain amino acid degradation and of � 16/49 oxidation that chemically resemЫe three successive steps of the citric acid cycle. Which steps are these? (3 pts) 19. Helicobacter pylori, the bacterium responsiЫe for gastric ulcers, can 17/52 survive in the stomach (where the рН is а slow as 1.5) in part because it synthesizes large amounts of the enzyme urease. (а) write the reaction for urea hydrolysis Ьу urease. (Ь) Explain why the reaction could help estaЫish а more hospitaЫe environment for н. pylori, which tolerates acid but prefers to grow near-neutral рН. ( 2 pts) Page 4 17/53 24. III. PATHWAYS. (20 points) Write out the eight steps in � oxidation from palmitate to myristyl-CoA (С14) plus acetyl-CoA, which includes three steps needed for transport. For each step give the name of the enzyme that catalyzes the reaction (no abbreviations), any cofactors required (abbreviations ОК), the name of each intermediate and their structures (including palmitate, myristyl-CoA, and acetyl-CoA; you can abbreviate phosphate and/or phosphoryl Ьу а circled "Р" and Coenzyme А as "СоА"), 29/105 (20 pts) (t1 L}- еоо-· А-т (J�� C{lilj())a о; С t1 � j�,c J Ccofeч/ 1 ✓ l \J \1 О · J/-T:r= сн Сл,/t /1 (, -, 0 L/1VV\ J ·т L 1) f Сl D Си,\.-,, j 11 с Q Lll L - S t-v4 YV)j,pJ, wn·v� 1 ? С/ 1Р с ,: с.,. s си tvt! fL� ..rlil)t'v\ 1 е,,11 -t �Сон ;,- Page 6 ✓ No. in No. on Q-Bank Test Correct Answer 13 1:3, 15 15 14 10 1:3 14 13 13 15 14 10 15 14 19 16 11 22 20 23 18 16 6 3 21 42 28 8 87 1 D 3 4 с 2 6 7 8 9 10 11 12 13 14 15 16 D в в ЛG ЛG ЛG ЛG ЛG RTln([K+(in)]/[K+ (out)]) + z�ЛЧ' (8.3)(310)ln(150/4) + (1)(97000)(-0.06) (2.57)kJ/mol(3.6) + (-5,8)kJ/mol (9.3)kJ/mol - (5,8)kJ/mol + 3.5 kJ/mol, or about 4 в с в с с с в D с в G; Р; G+P; ()r- о у-- -) Ц, {-f 15 32 17 С; В; А, D; Е 13 35 18 14 59 19 13 24 (а) со+ ; (Ь) glucose; (с) Fe2+; (d) acetate; (е ) ethanol (f) acetaldehyde. The glycolytic pathway is so central to all of cellular metabolism that mutations in glycolytic enzymes are lethal; embryos with such mutations do not develop. 20 дG 0 ' is а physical constant, characteristic of each chemical reaction. дG is а variaЫe that depends on дG 0 ', the temperature, and the concentrations of all reactants and products: дG = дG 0 ' 1-;:-_ 1� L�Г 15 52 14 64 21 + RT ln [ product] (reactant] Succinate acts "catalytically" as an intermediate in the citric acid cycle; it is not consumed but is regenerated Ьу the operation of the cycle. Its addition to an extract depleted in citric acid cycle intermediates allows the cycle to resume operating, oxidizing acetyl-CoA to СО2 , 22 Anaerobic metabolism of glucose (fermentation to lactate) produces 2 АТР per glucose; based on the assumption, aerobic metabolism (oxidation to со2) yields 36 АТР per glucose. For yeast to produce about the same amount of АТР, 18 times more glucose will Ье consumed anaerobically relative to aerobic consumption. 14 82 2 3 Phosphofructokinase-1 is inhibited allosterically Ьу АТР and citrate, and is activated Ьу АМР, ADP, and fructose-2,6-bisphosphate. 10 51 2 4 The graph does not indicate the involvement of а transport protein, since the rate does not saturate at hign (Х]. You could verify this you could increase the (Х] further (perhaps you are only seeing the very {1r�+ p1,,Jc,,,{Cu(vQ. ое_- \.IJl,L, ·,1\1,.1,;.\1t,, 1 + h�l'\'\.t-Q � '[>vbt,,.\<,.J,1f"> У21 :°)1'YV(,+,t.,\., o 1/?i'� } 14 1}) - (21_) 1 er.�11,,c I\IИYl(,, /,Q NAo 1 A:1(J /ч Lt,s:--) ) ('6,5') L (11:>) J (1) J ll) (1) (i) No. in No. on Q-Bank Test Correct Answer 17 18 17 19 16 17 8 1 17 18 1 23 З 4 5 6 5 2 Е А с с с А с_ JL-,., ,..,v - v_,.D::,,,v__, -----...,�-�----1� l=- --f----'�:::..+.l,,,.,.,.. 7 --, А 9 -Г8 14 4 10 Е 17 В 18 7 11 �� -=- 2� -= '-- �� :..::. 17 18 18 18 16 29 в D �=--- Ff itь 1::1) z:p Ь ,\ С 1• с. •f -=� :----'� -16 А /' l_ft,J;, Tryptophan can Ье considered а member of this group since its 17 alpha amino acid and beta carbons result in the formation of Ala, which goes to pyruvate via transamination. 1. Succinate dehydrogenase (НОО С-СН2-СН 2 -СООН --> НООС-НС=СН49 18 СООН (trans)), using FAD 2. Fumarase (НООС-НС=СН-СООН (trans) --> НООССНОН-СН2-СООН) 3. Malate dehydrogenase (НО ОССН ОН-СН 2-СООН --> НООС-С=О-СН2 СООН), using NAD+ H 2 N-C=O-NH 2 (urea) + Н2 O ----> 2 NH 3 + СО 2 52 19 (а) (Ь) The NH 3 produced Ьу the action of urease can combine with protons in gastric fluid to form NH4 +, This could reduce the concentration о and therefore increase the рН. 20 55 An АТР Synthase with more с ubuints requires more proton translocation events to е complete rotation the с ring. Consequently, more substrate oxidation (02 t on) is required to syn ze the 3 АТР molecules per rotation. An F0 with 9 nt would require 9 protons translocated per З АТР, and one with 12 would req ire 1 protons translocated per 3 АТР. If N� Н xidation to о2 pumps 10-12 protons and F0 with 10 с subunits has а Р/O ratio of 2.5, then an F0 with 9 с subunits would only require 9 protons/rotation or 10/9 (=1.1) the Р/O ratio of one with 10 с ubunits, or а Р/O ratio of 1.lx2.5 = 2.8; and an F 0 with 12 с subunits would hav. а /О ratio of (10/12 08.Зх2.5 =) 2.1. 8 0: 21 The label appears as 56 (СН2О) + 1 8 0 2------- --- (/ н/8 0 + COz__! light --=-=- '/2 UQH2 -бt �- �"'-""'f -� - �(а + а� 0 2 23 22 Е 0 ' for 0 2 must Ье the larger positive value (+О.82), because electron flow occurs spontaneously to the electron acceptor with the more positive Е 0 ' . Six cycles are required 50 23 С2 (acetyl-CoA) = З СЗ (propionyl-CoA) = 3 С4 (methylpropionyl (isobutryl)-CoA) = 1 105 24 names of enzymes (8), names of substrates (4.5), structures of substrates (4.5), cosubstrates for synthetase (1), carnitine & СоА (1), other cofactors (1) --=-� �-� � 18 17 53 16 с4 Е ✓�-