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The Citric Acid Cycle, Exams of Nursing

Walden UniversityNursing

A detailed overview of the citric acid cycle, also known as the krebs cycle or tricarboxylic acid (tca) cycle. It covers various aspects of this fundamental metabolic pathway, including the formation of intermediates, the generation of nadh and fadh2, the oxidation of acetyl-coa, and the regulation of key enzymes. The document also explores the role of the citric acid cycle in energy production, the synthesis of biomolecules, and the interconnections with other metabolic processes. By studying this document, students can gain a comprehensive understanding of the citric acid cycle, its significance in cellular metabolism, and its broader implications in biological systems.

Typology: Exams

2023/2024

Available from 08/22/2024

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The Citric Acid Cycle
actual solution
10. In mammals, each of the following occurs during the citric acid
cycle except:
A) formation of -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. - answer โœ…โœ…D
11. 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
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The Citric Acid Cycle

actual solution

  1. In mammals, each of the following occurs during the citric acid cycle except: A) formation of -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. - answer โœ…โœ… D
  2. 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/ C) 1/

D) 1/

E) 3/4 - answer โœ…โœ… B

  1. 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. - answer โœ…โœ… B
  2. 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 - answer โœ…โœ… E
  3. The two moles of CO2 produced in the first turn of the citric acid cycle have their origin in the:

C) malate to oxaloacetate. D) succinyl-CoA to succinate. E) Alpha-ketoglutarate to succinyl-CoA. - answer โœ…โœ… E

  1. 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) Alpha-Ketoglutarate dehydrogenase complex - answer โœ…โœ… E
  2. 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. - answer โœ…โœ… E
  1. The standard reduction potentials (E'ยฐ) for the following half reactions are given. Fumarate + 2H+ + 2e- -->succinate E'ยฐ = +0.031 V FAD + 2H+ + 2e- -->FADH2 E'ยฐ = -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 FADH 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. - answer โœ…โœ… B
  2. Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA? A) ATP B) CoA-SH

B) malate dehydrogenase. C) pyruvate dehydrogenase D) succinate dehydrogenase. E) the alpha-ketoglutarate dehydrogenase complex. - answer โœ…โœ… D

  1. 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+ - answer โœ…โœ… C
  2. 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. - answer โœ…โœ… E
  1. Which of the following intermediates of the citric acid cycle is prochiral? A) Citrate B) Isocitrate C) Malate D) Oxaloacetate E) Succinate - answer โœ…โœ… A
  2. Anaplerotic reactions. A) produce oxaloacetate and malate to maintain constant levels of citric acid cycle intermediates B) produce biotin needed by pyruvate carboxylase C) recycle pantothenate used to make CoA D) produce pyruvate and citrate to maintain constant levels of citric acid cycle intermediates E) All of the above - answer โœ…โœ… A
  3. Intermediates in the citric acid cycle are used as precursors in the biosynthesis of: A) amino acids.
  1. 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. - answer โœ…โœ… D
  2. 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+ - answer โœ…โœ… E
  3. 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. - answer โœ…โœ… E

  1. 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 thioester of acetate. B) The methyl (โ€”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. - answer โœ…โœ… A
  2. 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) 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. - answer โœ…โœ… A

  1. 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. - answer โœ…โœ… E
  2. 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 - answer โœ…โœ… B

  1. Which of the following is not an intermediate of the citric acid cycle? A) Acetyl-CoA B) Citrate C) Oxaloacetate D) Succinyl-CoA E) Alpha-Ketoglutarate - answer โœ…โœ… A