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There are 2 0 Multiple Choice questions, each worth 5 pt. Your answers must be marked on the Scantron sheet. v If you have any question about the interpretation of a question or answer, please let me (Dr.G.) know. I can add info to this answer key, and notify the class of the update. ý If you think that you have stumped me, þ Some questions have more than one correct answer. If so, choose only one answer.
ý The parts of any answer that made it incorrect are marked in italics (and colored red).
Thank you, and have an exciting second half of the semester!
1. Some of the enzymes named below catalyze oxidative decarboxylations; some catalyze thioester
formation. Which pair of enzymes does NOT match the description given for it?
a. oxidative decarboxylation with and without thioester formation: pyruvate dehydrogenase, Malic enzyme b. thioester formation without oxidative decarboxylation: fatty acyl CoA synthetase c. thioester formation with and without oxidative decarboxylation: α-ketoglutarate dehydrogenase, fatty acyl CoA synthetase d. oxidative decarboxylation coupled (ok) (NOT coupled) to thioester formation: α-ketoglutarate dehydrogenase, fatty acyl CoA synthetase
2. One relationship between glycolysis and gluconeogenesis is NOT:
a. Muscle cells release lactic acid as an end-product of glycolysis, and liver cells use gluconeogenesis to convert this lactic acid back to glucose. b. They are both stimulated by low blood sugar, and inhibited by high concentrations of energy-rich metabolites within the cell. No, they are regulated reciprocally.
c. They can occur simultaneously within a single cell. Again, not if reciprocally regulated!
d. They differ only in the enzymes that catalyze the irreversible steps.
3. Fortunately, during periods of intense exercise, muscle cells continue to obtain energy from glucose
because:
a. pyruvate can be converted to alanine and used for protein synthesis.
b. pyruvate is reduced to lactate, which is converted to glucose by gluconeogenesis in the liver
c. excess pyruvate which cannot enter the mitochondria is converted to highly-inflammable ketone bodies. d. exercising muscle cells can convert lactate to glucose via gluconeogenesis.
4. Which of the following enzyme pairs is NOT reciprocally regulated?
a. Citrate synthase vs. isocitrate dehydrogenase.
b. Pyruvate kinase vs. phosphoenolpyruvate carboxykinase c. Phosphofructokinase vs. fructose-1,6-bisphosphatase d. Pyruvate dehydrogenase vs. pyruvate carboxylase
5. A "Healthy Eating" feature in the Lawrence Journal-World quotes a "nutrition expert" as saying
that eating sugar robs you of energy because you use more energy to digest glucose than you get
back out of it. This notion might be based on the fact that:
a. Glycolysis under strictly anaerobic conditions yields only 2 ATP per glucose
b. In the absence of oxygen, there is no net gain of energy (ATP or NADH) from breakdown of glucose. c. If exercising humans could convert pyruvate to ethanol, they'd pass out. d. Glycolysis requires an initial investment of 2 ATP per glucose.
6. Low levels of ATP and NADH, coupled with high levels of Ac-SCoA, will favor conversion of
pyruvate to:
a. CO 2 via Ac-SCoA b. Fatty acids via citrate c. CO 2 via oxaloacetate
d. Glucose via OAA
7. The conversion of pyruvate to Acetyl~CoA, vs. its conversion to oxaloacetate (OAA), differ in that:
a. The energy of the bond between the acetyl and carboxylate parts of pyruvate is conserved as a thioester
bond in Acetyl~CoA, but is unchanged in OAA.
b. CO 2 is released from Pyr during the formation of Acetyl~CoA, whereas CO 2 is added to Pyr to form
OAA.
c. The pyruvate dehydrogenase reaction is essentially irreversible because CO 2 is the leaving group, whereas
the pyruvate carboxylase reaction is irreversible because it is coupled to phosphoryl transfer from ATP.
d. all of the above
e. none of the above < this is the only time answer "e" is used >
8. Consider the citric acid cycle (CAC) and the mitochondrial electron transport system (ETS) as two
separate "black boxes." Which of the following statements best describes the relationship between
the two systems?
a. The CAC provides NADH and FADH 2 for the ETS.
b. The CAC provides succinyl~CoA, GTP , and NADH for the ETS. c. The CAC provides FADH 2 , NADH, and oxygen for the ETS. d. The CAC provides NADH, ubiquinone , and oxygen for the ETS.
9. Some of the energy-conserving steps in the citric acid cycle are:
a. the pyruvate dehydrogenase, malate dehydrogenase, and substrate-level phosphorylation reactions b. -ketoglutarate dehydrogenase, isocitrate dehydrogenase, succinyl-CoA synthetase (or lyase), succinate dehydrogenase, and malate dehydrogenase.
c. -ketoglutarate dehydrogenase, cytochrome c, and oxidation of ubiquinone. d. glycerol-3-phosphate dehydrogenase, the malate-aspartate shuttle, and formation of a proton gradient.
10. If the citric acid cycle were like a cafeteria, pyruvate could be transformed into the
(acetyl groups) or the dinner (oxaloacetate). Which one of the following situations never
happens?
a. When concentrations of ATP, NADH, and Ac~SCoA are all low , pyruvate dehydrogenase puts more dinner on the plates. b. When [ATP], [NADH], and [Ac~SCoA] are all high , dinner is not served, and gluconeogenesis puts the plates into storage. c. When [ATP], [NADH], and [succinyl-CoA] are all high , more and more dinners [NOTE: served on plates !] will be served (until everyone bursts).
d. When [ATP] and [NADH] are low , but [Ac~SCoA] is high , pyruvate carboxylase puts out more plates.
11. In order to generate a proton gradient during electron transport, electrons must be transferred from
one redox center (redox-active molecule) to the next along which of the following paths?
Input (start) Output (end) a. H 2 O > Fe2+^ > QH 2 > FADH 2 > NADH b. FADH 2 > Fe2+^ > NADH > QH 2 > H 2 O c. NADH > FADH 2 > QH 2 > Fe2+^ > H 2 O
d. NADH > FADH 2 > H 2 O > Fe2+^ > QH 2
a. G 0 because transfer of fatty acyl groups between HS-CoA and carnitine is readily reversible.
b. G>0 because in the -ketoglutarate dehydrogenase reaction, release of coenzyme A is accompanied by the synthesis of GTP from GDP and Pi. c. G>0 because ATP must be used to activate fatty acids prior to transferring them to CoA. d. G<0 because transfer of a fatty acyl chain from S-CoA to carnitine occurs without any energy input.
17. The fatty acid synthase enzyme complex has 2 active sites. Having phosphopantotheine as the
malonyl (monomer) site attachment residue, and Cys as the attachment site for the acyl (polymer)
site, is advantageous because ...
a. the thioester bonds are easy to hydrolyze b. transfer of the newly-elongated (n+2) fatty acyl chain from the monomer site back to the polymer site, and replenishment of the monomer site, can be done without any energy expenditure
c. attachment of the newly-elongated fattyl acyl chain to a long pantotheine "arm" at the malonyl site allows the acyl chain to be transferred successively to the active sites for reduction, dehydration, and reduction, and back to the Cys at the acyl site The pantotheine acts like a robotic arm in an assembly line!
d. this combination allows the condensation (elongation) reaction to proceed without any energy expenditure
18. The first committed step of fatty acid biosynthesis is:
a. formation of citrate, which is transported out of the mitochondrion and stimulates acetyl CoA carboxylase. b. formation of palmitate, which may be incorporated into phospholipids. c. formation in the cytoplasm of acetyl-CoA and NADPH, both necessary for fatty acid biosynthesis d. formation of malonyl~SCoA, which represents activated acetyl groups.
19. When a cell is actively synthesizing fatty acids, how is the breakdown of the newly-synthesized fatty
acid prevented?
a. high concentrations of Acetyl~CoA from the citric acid cycle inhibit carnitine acyl Transferase II in the mitochondrial matrix. b. high concentrations of newly-synthesized palmitoyl~SCoA cross-inhibit the cytoplasmic fatty acyl-CoA synthetase c. high concentrations of citrate, which activate acetyl-CoA carboxylase, also inhibit fatty acyl-CoA synthetase d. high concentrations of malonyl~SCoA diffuse in the inter-membrane space and inhibit transfer of fatty acyl chains from CoA to carnitine (by fatty acyl:carnitine acyl transferase, or Transferase I)
20. A person who is deficient in the enzyme fructose-1,6-bisphosphatase in the liver would probably
experience:
a. inability to metabolize fructose. b. inability to resynthesize glucose from lactate produced during exercise.
c. failure to synthesize fats when the diet contained excess carbohydrate. d. inability to convert fructose-1,6-bisphosphate into triose phosphate
