16 - QUIZZES - Citric Acid Cycle
15. (Reactions of Citric Acid Cycle) The oxidative decarboxylation of α-ketoglutarate proceeds by means of multistep reactions in which All BUT One of the following Cofactors are required. Which one is NOT required? A) ATP B) Coenzyme A C) Lipoic acid D) NAD+ E) Thiamine pyrophosphate
(A) ATP
2. (Production of Acetyl-CoA: ACTIVATED Acetate) Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA? A) ATP B) CoA-SH C) FAD D) Lipoic acid E) NAD+
(A) ATP
6. (Reactions of Citric Acid Cycle) Which of the following is NOT TRUE of the citric acid cycle? A) All enzymes of the cycle are located in the cytoplasm, except succinate dehydrogenase, which is bound to the inner mitochondrial membrane. B) In the presence of malonate, one would expect succinate to accumulate. C) Oxaloacetate is used as a substrate but is not consumed in the cycle. D) Succinate dehydrogenase channels electrons directly into the electron transfer chain. E) The condensing enzyme is subject to allosteric regulation by ATP and NADH.
(A) All enzymes of the cycle are located in the cytoplasm, except succinate dehydrogenase, which is bound to the inner mitochondrial membrane.
1. (Production of Acetyl-CoA: ACTIVATED Acetate) Which of the following is NOT TRUE of the reaction catalyzed by the pyruvate dehydrogenase complex? A) Biotin participates in the decarboxylation. B) Both NAD+ and a flavin nucleotide act as electron carriers. C) The reaction occurs in the mitochondrial matrix. D) The substrate is held by the lipoyl-lysine "swinging arm." E) Two different cofactors containing —SH groups participate.
(A) Biotin participates in the decarboxylation.
24. (Reactions of Citric Acid Cycle) Which of the following intermediates of the citric acid cycle is Prochiral? A) Citrate B) Isocitrate C) Malate D) Oxaloacetate E) Succinate
(A) Citrate
4. (Production of Acetyl-CoA: ACTIVATED Acetate) Which of the following statements about the Oxidative Decarboxylation of Pyruvate in Aerobic conditions in Animal cells is CORRECT? A) One of the products of the reactions of the pyruvate dehydrogenase complex is a thirster of Acetate. B) The methyl (—CH3) group is eliminated as CO2. C) The process occurs in the cytosolic compartment of the cell. D) The pyruvate dehydrogenase complex uses all of the following as cofactors: NAD+, lipoic acid, pyridoxal phosphate (PLP), and FAD. E) The reaction is so important to energy production that pyruvate dehydrogenase operates at full speed under all conditions.
(A) One of the products of the reactions of the pyruvate dehydrogenase complex is a thirster of Acetate.
30. (The Glyoxylate Cycle) The Glyoxylate Cycle is: A) a means of using acetate for both energy and biosynthetic precursors. B) an alternative path of glucose metabolism in cells that do not have enough O2. C) defective in people with phenylketonuria. D) is not active in a mammalian liver. E) the most direct way of providing the precursors for synthesis of nucleic acids (e.g., ribose).
(A) a means of using acetate for both energy and biosynthetic precursors.
28. (The Glyoxylate Cycle) During seed germination, the glyoxylate pathway is important to plants because it enables them to: A) carry out the net synthesis of glucose from acetyl-CoA. B) form acetyl-CoA from malate. C) get rid of isocitrate formed from the aconitase reaction. D) obtain glyoxylate for cholesterol biosynthesis. E) obtain glyoxylate for pyrimidine synthesis.
(A) carry out the net synthesis of glucose from acetyl-CoA.
8) What Types of Reactions do Phosphorylases Catalyze? A. Displacement reactions in which an attacking Phosphate becomes Covalently attached at the Point of Bond Breakage. B. The removal of a phosphoryl group from a phosphate ester. C. The transfer of a phosphoryl group from a nucleoside triphosphate to an acceptor molecule. D. Ligation reactions in which phosphate esters join molecules.
(A). Displacement reactions in which an attacking Phosphate becomes Covalently attached at the Point of Bond Breakage.
3) The FIRST reaction of the Citric Acid Cycle, which generates Citrate, is A. a condensation reaction. B. an oxidative decarboxylation reaction. C. dehydrogenation reaction. D. a dehydration reaction.
(A). a Condensation reaction
17) Anaplerotic reactions, such as the conversion of Pyruvate to Oxaloacetate, are useful to the Citric Acid Cycle because they A. generate a steady supply of intermediates for the citric acid cycle. B. produce molecules needed to regulate the citric acid cycle. C. link the citric acid cycle to the glyoxylate cycle. D. siphon away excess intermediates from the citric acid cycle.
(A). generate a steady supply of intermediates for the citric acid cycle.
13) The Citric Acid Cycle is an Amphibolic Pathway, which means that A. it serves in BOTH Anabolic and Catabolic processes. B. it is linked to other cycles. C. it can catalyze reactions that are BOTH Exergonic and Endergonic. D. it can move in BOTH a Forward and Reverse direction.
(A). it serves in BOTH Anabolic and Catabolic processes.
19. (Reactions of Citric Acid Cycle) The standard reduction potentials (E'°) for the following half reactions are given. Fumarate + 2H+ + 2e- → succinate E'° = +0.031 V FAD + 2H+ + 2e- → FADH2 E'° = -0.219 V If succinate, fumarate, FAD, and FADH2, all at l M concentrations, were mixed together in the presence of succinate dehydrogenase, which of the following would happen initially? A) Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced. B) Fumarate would become reduced; FADH2 would become oxidized. C) No reaction would occur because all reactants and products are already at their standard concentrations. D) Succinate would become oxidized; FAD would become reduced. E) Succinate would become oxidized; FADH2 would be unchanged because it is a cofactor, not a substrate.
(B) Fumarate would become reduced; FADH2 would become oxidized.
1) Cellular Respiration is the process by which cells A. oxidize organic fuels to CO2 and H2O. B. consume O2 and produce CO2. C. convert O2 to H2O. D. breakdown sugars to CO2 and H2O.
(B). Cellular Respiration is the Process by which cells Consume O2 and Produce CO2.
15) Which of the following Citric Acid Cycle reaction steps is NOT Inhibited by a HIGH [NADH]/[NAD+]? A. conversion of α-ketoglutarate to succinyl-CoA B. conversion of succinyl-CoA to succinate C. conversion of isocitrate to α-ketoglutarate D. condensation of oxaloacetate and acetyl-CoA to form citrate
(B). Conversion of Succinyl-CoA to Succinate (is NOT inhibited by a High ratio of NADH to NAD+)
9) Which of the following enzymes catalyzes a CONDENSATION reaction in which NO Nucleoside Triphosphate is required as an Energy source? A. kinases B. synthases C. ligases D. synthetases
(B). Synthases
5) Which of the following is TRUE about the Pyruvate Dehydrogenase Complex? A. It converts pyruvate to oxaloacetate. B. It catalyzes oxidative decarboxylation. C. It is located in the cytosol of eukaryotic cells. D. It requires NADH.
(B). it CATALYZES Oxidative Decarboxylation
22. (Reactions of Citric Acid Cycle) Which of the following cofactors is required for the conversion of succinate to fumarate in the citric acid cycle? A) ATP B) Biotin C) FAD D) NAD+ E) NADP+
(C) FAD
4) For every molecule of Glucose, how many molecules of CO2 are Released in the Citric Acid Cycle? A. 1 B. 2 C. 4 D. 6
(C). 4
6) What role does Coenzyme A play in the Citric Acid Cycle? A. It is an electron carrier. B. It carries hydride ions. C. It is an acyl group carrier. D. It is an oxidizing agent.
(C). It is an Acyl group Carrier.
25. (Reactions of Citric Acid Cycle) The conversion of 1 mol of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the citric acid cycle also yields _____ mol of NADH, _____ mol of FADH2, and _____ mol of ATP (or GTP). A) 2; 2; 2 B) 3; 1; 1 C) 3; 2; 0 D) 4; 1; 1 E) 4; 2; 1
(D) 4; 1; 1
5. (Production of Acetyl-CoA: ACTIVATED Acetate) Glucose labeled with 14C in C-3 and C-4 is completely converted to acetyl-CoA via glycolysis and the pyruvate dehydrogenase complex. What percentage of the acetyl-CoA molecules formed will be labeled with 14C, and in which position of the acetyl moiety will the 14C label be found? A) 100% of the acetyl-CoA will be labeled at C-1 (carboxyl). B) 100% of the acetyl-CoA will be labeled at C-2. C) 50% of the acetyl-CoA will be labeled, all at C-2 (methyl). D) No label will be found in the acetyl-CoA molecules. E) Not enough information is given to answer this question.
(D) No label will be found in the acetyl-CoA molecules.
20. (Reactions of Citric Acid Cycle) For the following reaction, ΔG'° = 29.7 kJ/mol. L-Malate + NAD+ → oxaloacetate + NADH + H+ The reaction as written: A) can never occur in a cell. B) can only occur in a cell if it is coupled to another reaction for which ΔG'° is positive. C) can only occur in a cell in which NADH is converted to NAD+ by electron transport. D) may occur in cells at certain concentrations of substrate and product. E) would always proceed at a very slow rate
(D) may occur in cells at certain concentrations of substrate and product.
21. (Reactions of Citric Acid Cycle) Page: 612 Difficulty: 1 Ans: D All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD+ except the reaction catalyzed by: A) isocitrate dehydrogenase. B) malate dehydrogenase. C) pyruvate dehydrogenase D) succinate dehydrogenase. E) the α-ketoglutarate dehydrogenase complex.
(D) succinate dehydrogenase
26. (Regulation of Citric Acid Cycle) Entry of acetyl-CoA into the citric acid cycle is decreased when: A) [AMP] is high. B) NADH is rapidly oxidized through the respiratory chain. C) the ratio of [ATP]/[ADP is low D) the ratio of [ATP]/[ADP] is high. E) the ratio of [NAD+]/[NADH] is high.
(D) the Ratio of [ATP]/[ADP] is high.
2) Amino Acids, Fatty Acids, and Glucose are Oxidized and Enter the Citric Acid Cycle as A. Pyruvate. B. Acetate. C. Oxaloacetate. D. Acetyl-CoA.
(D). Acetyl-CoA.
14) Biotin A. serves as a cofactor in dehydrogenation reactions. B. transfers one-carbon groups. C. is a cofactor that transfers acetyl groups. D. carries CO2 groups.
(D). Carries CO2 groups
7) Which of following is TRUE about ALL of the Dehydrogenase enzymes that participate in the Citric Acid Cycle? A. They catalyze condensation reactions. B. They generate CO2. C. They convert a single bond to a double bond. D. They generate REDUCED electron carriers.
(D). They generate REDUCED electron carriers.
10) Which of the following conditions has a NEGATIVE effect on the Pyruvate Dehydrogenase Complex? A. a High ratio of [ADP]/[ATP] B. a High level of Ca2+ C. a High ratio of [NAD+]/[NADH] D. a High ratio of [Acetyl-CoA]/[CoA]
(D). a HIGH ratio of [Acetyl-CoA]/[CoA] (has a NEGATIVE effect on the PDH Complex)
27. (Regulation of Citric Acid Cycle) Citrate synthase and the NAD+-specific isocitrate dehydrogenase are two key regulatory enzymes of the citric acid cycle. These enzymes are inhibited by: A) acetyl-CoA and fructose 6-phosphate. B) AMP and/or NAD+. C) AMP and/or NADH. D) ATP and/or NAD+. E) ATP and/or NADH.
(E) ATP and/or NADH.
13. (Reactions of Citric Acid Cycle) Which one of the following is not associated with the oxidation of substrates by the citric acid cycle? A) All of the below are involved. B) CO2 production C) Flavin reduction D) Lipoic acid present in some of the enzyme systems E) Pyridine nucleotide oxidation
(E) Pyridine nucleotide oxidation
3. (Production of Acetyl-CoA: ACTIVATED Acetate) Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA? A) Biotin, FAD, and TPP B) Biotin, NAD+, and FAD C) NAD+, biotin, and TPP D) Pyridoxal phosphate, FAD, and lipoic acid E) TPP, lipoic acid, and NAD+
(E) TPP, Lipoic Acid, and NAD
29. (The Glyoxylate Cycle) A function of the glyoxylate cycle, in conjunction with the citric acid cycle, is to accomplish the: A) complete oxidation of acetyl-CoA to CO2 plus reduced coenzymes. B) net conversion of lipid to carbohydrate. C) net synthesis of four-carbon dicarboxylic acids from acetyl-CoA. D) net synthesis of long-chain fatty acids from citric acid cycle intermediates. E) both B and C are correct
(E) both B and C are correct; (B) Net conversion of lipid to carbohydrate & (C) Net synthesis of four-carbon dicarboxylic acids from acetyl-CoA.
23. (Reactions of Citric Acid Cycle) In the citric acid cycle, a flavin coenzyme is required for: A) condensation of acetyl-CoA and oxaloacetate. B) oxidation of fumarate. C) oxidation of isocitrate. D) oxidation of malate. E) oxidation of succinate.
(E) oxidation of succinate.
18. (Reactions of Citric Acid Cycle) The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP) by Substrate Level Phosphorylation is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinate to fumarate. E) succinyl-CoA to succinate.
(E) succinyl-CoA to succinate.
14. (Reactions of Citric Acid Cycle) The two moles of CO2 produced in the first turn of the citric acid cycle have their origin in the: A) carboxyl and methylene carbons of oxaloacetate B) carboxyl group of acetate and a carboxyl group of oxaloacetate. C) carboxyl group of acetate and the keto group of oxaloacetate. D) two carbon atoms of acetate. E) two carboxyl groups derived from oxaloacetate.
(E) two carboxyl groups derived from oxaloacetate.
17. (Reactions of Citric Acid Cycle) Which one of the following enzymatic activities would be decreased by thiamine deficiency? A) Fumarase B) Isocitrate dehydrogenase C) Malate dehydrogenase D) Succinate dehydrogenase E) α-Ketoglutarate dehydrogenase complex
(E) α-Ketoglutarate dehydrogenase complex
16. (Reactions of Citric Acid Cycle) The reaction of the citric acid cycle that is most similar to the pyruvate dehydrogenase complex catalyzed conversion of pyruvate to acetyl-CoA is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinyl-CoA to succinate. E) α-ketoglutarate to succinyl-CoA.
(E) α-ketoglutarate to succinyl-CoA.
16)
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***2 Oxidative Decarboxylation reaction steps
1 Glucose GENERATES 2 Acetyl-CoA, EACH of which Enters the Citric Acid Cycle & Releases 2 molecules of CO2 - 1 molecule at EACH of 2 Oxidative Decarboxylation reaction steps (4 total).
9. (Reactions of Citric Acid Cycle) Which of the following is not an intermediate of the citric acid cycle? A) Acetyl-coA B) Citrate C) Oxaloacetate D) Succinyl-coA E) α-Ketoglutarate
A) Acetyl-coA
7. (Reactions of Citric Acid Cycle) Acetyl-CoA labeled with 14C in both of its acetate carbon atoms is incubated with unlabeled oxaloacetate and a crude tissue preparation capable of carrying out the reactions of the citric acid cycle. After one turn of the cycle, oxaloacetate would have 14C in: A) all four carbon atoms. B) no pattern that is predictable from the information provided. C) none of its carbon atoms. D) the keto carbon and one of the carboxyl carbons. E) the two carboxyl carbons.
A) all four carbon atoms.
Organic Fuel (molecules)
Amino Acids, Fatty Acids, & Glucose serve as ________ ______ molecules that are OXIDIZED and ENTER the Citric Acid Cycle as Acetyl-CoA.
12. (Reactions of Citric Acid Cycle) Conversion of 1 mol of acetyl-CoA to 2 mol of CO2 and CoA via the citric acid cycle results in the Net Production of: A) 1 mol of citrate. B) 1 mol of FADH2. C) 1 mol of NADH. D) 1 mol of oxaloacetate. E) 7 mol of ATP.
B) 1 mol of FADH2.
11. (Reactions of Citric Acid Cycle) Oxaloacetate uniformly labeled with 14C (i.e., with equal amounts of 14C in each of its carbon atoms) is condensed with unlabeled acetyl-CoA. After a single pass through the citric acid cycle back to oxaloacetate, what fraction of the original radioactivity will be found in the oxaloacetate? A) all B) 1/2 C) 1/3 D) 1/4 E) 3/4
B) 1/2
8. (Reactions of Citric Acid Cycle) Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which of the following compounds would you expect to decrease in concentration? A) Citrate B) Fumarate C) Isocitrate D) Pyruvate E) Succinate
B) Fumarate
(Type of Reaction): CARBOXYLATION
Biotin, which is a COFACTOR in ____________ reactions, is a specialized carrier of CO2 groups. For example, it serves as the Prosthetic group of the enzyme Pyruvate Carboxylase, which TRANSFERS a CO2 group to Pyruvate to generate Oxaloacetate.
Ligases
Catalyze Condensation reactions in which 2 atoms are JOINED using the Energy of ATP or Another Energy source.
Synthases
Catalyze Condensation reactions in which NO Nucleoside Triphosphate is required as an Energy source.
Synthetases
Catalyze Condensation reactions that USE ATP or Another Nucleoside Triphosphate as an Energy source.
Consume O2 & Produce CO2
Cellular Respiration is the process by which cells __________ & __________
ACTIVATES (them for group) TRANSFER (to Other molecules)
Coenzyme A forms a Thioester Bond with Acyl groups and ________ them for group _________ to other molecules.
10. (Reactions of Citric Acid Cycle) In mammals, each of the following occurs during the Citric Acid Cycle except: A) formation of α-ketoglutarate. B) generation of NADH and FADH2. C) metabolism of acetate to carbon dioxide and water. D) net synthesis of oxaloacetate from acetyl-CoA. E) oxidation of acetyl-CoA.
D) net synthesis of oxaloacetate from acetyl-CoA.
Serves in BOTH Catabolic & Anabolic processes.
In Aerobic organisms, the Citric Acid Cycle is an Amphibolic Pathway, meaning that it ? (see p. 631)
Coenzyme A -(activates)-> Acetate -(transfer to)-> Oxaloacetate -(forms)-> Citrate
In the Citric Acid Cycle, Coenzyme A ACTIVATES Acetate, allowing its TRANSFER to Oxaloacetate to FORM Citrate.
Kinases
KINASES DO NOT catalyze Condensation reactions; they Catalyze the TRANSFER of a Phosphoryl group from a Nucleoside Triphosphate such as ATP to an ACCEPTOR molecule.
(Type of Reaction): CONDENSATION
The 1st reaction of the Citric Acid Cycle is a CONDENSATION Reaction that Combines Oxaloacetate with Acetyl-CoA to form Citrate. This Condensation DOES NOT involve the Removal of the Elements of Water.
NADH & FADH2
The 4 Dehydrogenase Enzymes that participate in the Citric Acid Cycle TRANSFER electrons to the Coenzymes NAD+ or FAD to generate the REDUCED electron carriers _____ & _____, which in turn TRANSFER electrons in the Respiratory Chain.
ALLOSTERICALLY Inhibited
The Pyruvate Dehydrogenase Complex, which converts Pyruvate to Acetyl-CoA is ____________ ___________ when ratios of [ATP]/[ADP], [NADH]/[NAD+], and [acetyl-CoA]/[CoA] are High, indicating an Energy-sufficient Metabolic state.
Oxidative Decarboxylation
The Pyruvate dehydrogenase Complex CATALYZES the ________ ____________ of Pyruvate to RELEASE a CO2 & GENERATE Acetyl-CoA, which ENTERS the Citric Acid Cycle.
Generate NADH or that Commit a Substrate for ENTRY into the Citric Acid Cycle.
The Steps that are INHIBITED by a HIGH Ratio of [NADH] to [NAD+] are those that ?
HIGH Levels of NADH & ATP indicate a LOW Energy Demand
What conditions cause the Commitment of Acetyl-CoA to be INHIBITED for Entry into the Citric Acid Cycle?
Phosphorylases
________ Catalyze DISPLACEMENT reaction in which an attacking phosphate becomes COVALENTLY attached at the Point of Bond Breakage. (e.g. Glycogen Phosphorylase, which catalyzes Phosphorolysis of Glycogen, producing Glucose-1-Phosphate)
(Type of Reaction): ANAPLEROTIC
_________ reactions serve to REPLENISH intermediates, such as Oxaloacetate, in the Citric Acid Cycle. (see p. 631)
