Question 1

Which intermediate of the citric acid cycle is prochiral?

Accepted Answer

A)   citrate
B)   isocitrate
C)   malate
D)   oxaloacetate
E)   succinateF) All of the above
G) A) and B)

Question 2

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:

Accepted Answer

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.F) C) and D)
G) B) and D)

Question 3

Which statement is FALSE regarding regulation of the pyruvate dehydrogenase complex?

Accepted Answer

A)   In E. coli, a high ratio of [NAD+]/[NADH] activates the complex.
B)   In E. coli, high levels of ATP enhance the activity of pyruvate dehydrogenase kinase.
C)   In plants, NH4+ inhibits the complex by enhancing the activity of pyruvate dehydrogenase kinase.
D)   In mammals, both fatty acids and acetyl-CoA inhibit the complex.
E)   In skeletal muscle, both NAD+ and Ca2+ activate the complex.F) D) and E)
G) A) and D)

Question 4

Which step is NOT catalyzed by the pyruvate dehydrogenase complex?

Accepted Answer

A)   E1 catalyzes the decarboxylation of pyruvate.
B)   E1 catalyzes the oxidation of a hydroxyethyl group to an acetyl group.
C)   E2 catalyzes the transfer of an acetyl group to CoA-SH
D)   E3 catalyzes the reduction of oxidized lipoate.
E)   E3 catalyzes the transfer of electrons from FADH2 to NAD+.F) None of the above
G) A) and C)

Question 5

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?

Accepted Answer

A)   All
B)   1/2
C)   1/3
D)   1/4
E)   3/4F) B) and D)
G) D) and E)

Question 6

Which high-energy bond is associated with the succinyl-CoA synthetase reaction?

Accepted Answer

A)   acyl phosphate
B)   thioester
C)   phosphohistidine
D)   mixed anhydride
E)   All of the answers are correct.F) A) and B)
G) A) and D)

Question 7

CO2 is produced in two reactions in the citric acid cycle. For each of these reactions, name and show the structures of reactant and product, name the enzyme, and show how any cofactors participate.

Accepted Answer

The first reaction in the citric acid cy...

Question 8

The oxidative step of the citric acid cycle that is NOT linked to the reduction of NAD+ is the reaction catalyzed by:

Accepted Answer

A)   isocitrate dehydrogenase.
B)   malate dehydrogenase.
C)   pyruvate dehydrogenase
D)   succinate dehydrogenase.
E)   the  α\alphaα -ketoglutarate dehydrogenase complex. F) B) and C)
G) C) and D)

Question 9

Two of the steps in the oxidative decarboxylation of pyruvate to acetyl-CoA do not involve the three carbons of pyruvate, yet are essential to the operation of the pyruvate dehydrogenase complex. Explain.

Accepted Answer

The two steps in the oxidative decarboxy...

Question 10

Why is flux through the citric acid low in the resting state?

Accepted Answer

A)   Flux through the cycle is low due to a drop in serum adrenaline levels.
B)   Flux through the cycle is low due to allosteric inhibition of pyruvate carboxylase.
C)   Flux through the cycle is low due to complete oxidation of NADH because oxygen is readily available.
D)   Flux through the cycle is low due to low local concentrations of NAD+ because of a diminished rate of oxidative phosphorylation.
E)   Flux through the cycle is low due to product inhibition of the pyruvate dehydrogenase complex by ATP.F) None of the above
G) A) and B)

Question 11

The glyoxylate cycle in germinating seeds is a pathway that has some similarity to the citric acid cycle. It uses the carbon-based products from the catabolism of fatty acids as the precursors for gluconeogenesis. How can the glyoxylate cycle accomplish this?

Accepted Answer

A)   It produces an excess of citrate, which is exported out of the mitochondria.
B)   Its reactions take place partly in the matrix of the mitochondria and partly in the cytosol.
C)   It uses only the catabolic products of even-numbered, saturated fatty acids.
D)   Its reactions bypass the decarboxylation steps of the citric acid cycle.
E)   It prevents the formation of malate, allowing carbons from acetate to form oxaloacetate.F) A) and B)
G) B) and D)

Question 12

There are few, if any, humans with defects in the enzymes of the citric acid cycle. Explain this observation in terms of the role of the citric acid cycle.

Accepted Answer

The citric acid cycle, also known as the...

Question 13

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?

Accepted Answer

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.F) All of the above
G) C) and D)

Question 14

Which reaction of the citric acid cycle requires a water molecule?

Accepted Answer

A)   formation of citrate
B)   succinyl-CoA to succinate
C)   fumarate to malate
D)   All of the answers are correct.
E)   None of the answers is correct.F) B) and D)
G) None of the above

Question 15

Suppose you found an overly high level of pyruvate in a patient's blood and urine. One possible cause is a genetic defect in the enzyme pyruvate dehydrogenase, but another plausible cause is a specific vitamin deficiency. Explain what vitamin might be deficient in the diet, and why that would account for high levels of pyruvate to be excreted in the urine. How would you determine which explanation is correct?

Accepted Answer

The vitamin that might be deficient in t...

Question 16

Describe the enzymes, cofactors, intermediates, and products the pyruvate dehydrogenase complex.

Accepted Answer

The pyruvate dehydrogenase complex is a ...

Question 17

Arsenic inhibits the pyruvate dehydrogenase complex by inactivating the dihydrolipoamide component of dihydrolipoyl transacetylase. Which enzyme is also MOST likely to be inhibited by arsenic?

Accepted Answer

A)   GAP dehydrogenase
B)   isocitrate dehydrogenase
C)   succinyl-CoA synthetase
D)   malate dehydrogenase
E)    α\alphaα -ketoglutarate dehydrogenase F) A) and B)
G) A) and C)

Question 18

Which enzymatic activity would be decreased by thiamine deficiency?

Accepted Answer

A)   fumarase
B)   isocitrate dehydrogenase
C)   malate dehydrogenase
D)   succinate dehydrogenase
E)    α\alphaα -ketoglutarate dehydrogenase complex F) A) and C)
G) D) and E)

Question 19

Which statement is NOT true of the reaction catalyzed by the pyruvate dehydrogenase complex?

Accepted Answer

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.F) A) and E)
G) A) and B)

Question 20

Which vitamin is NOT a precursor for a cofactor in the pyruvate dehydrogenase complex?

Accepted Answer

A)   thiamine for TPP
B)   riboflavin for FAD
C)   niacin for lipoate
D)   nictotinamide for NAD+
E)   pantothenate for CoAF) All of the above
G) B) and C)

Exam 16: The Citric Acid Cycle

Why is flux through the citric acid low in the resting state?

Correct Answer
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Describe the enzymes, cofactors, intermediates, and products the pyruvate dehydrogenase complex.

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The pyruvate dehydrogenase complex is a ...
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Which statement is NOT true of the reaction catalyzed by the pyruvate dehydrogenase complex?

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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?

Correct Answer
verified

There are few, if any, humans with defects in the enzymes of the citric acid cycle. Explain this observation in terms of the role of the citric acid cycle.

Correct Answer
Answered by ExamLex AI
The citric acid cycle, also known as the...
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Which high-energy bond is associated with the succinyl-CoA synthetase reaction?

Correct Answer
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The oxidative step of the citric acid cycle that is NOT linked to the reduction of NAD⁺ is the reaction catalyzed by:

Correct Answer
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Correct Answer
Answered by ExamLex AI
The vitamin that might be deficient in t...
View Answer

Which statement is FALSE regarding regulation of the pyruvate dehydrogenase complex?

Correct Answer
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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:

Correct Answer
verified

Which reaction of the citric acid cycle requires a water molecule?

Correct Answer
verified

Which vitamin is NOT a precursor for a cofactor in the pyruvate dehydrogenase complex?

Correct Answer
verified

CO₂ is produced in two reactions in the citric acid cycle. For each of these reactions, name and show the structures of reactant and product, name the enzyme, and show how any cofactors participate.

Correct Answer
Answered by ExamLex AI
The first reaction in the citric acid cy...
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Which intermediate of the citric acid cycle is prochiral?

Correct Answer
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Arsenic inhibits the pyruvate dehydrogenase complex by inactivating the dihydrolipoamide component of dihydrolipoyl transacetylase. Which enzyme is also MOST likely to be inhibited by arsenic?

Correct Answer
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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?

Correct Answer
verified

Which enzymatic activity would be decreased by thiamine deficiency?

Correct Answer
verified

The glyoxylate cycle in germinating seeds is a pathway that has some similarity to the citric acid cycle. It uses the carbon-based products from the catabolism of fatty acids as the precursors for gluconeogenesis. How can the glyoxylate cycle accomplish this?

Correct Answer
verified

Two of the steps in the oxidative decarboxylation of pyruvate to acetyl-CoA do not involve the three carbons of pyruvate, yet are essential to the operation of the pyruvate dehydrogenase complex. Explain.

Correct Answer
Answered by ExamLex AI
The two steps in the oxidative decarboxy...
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Which step is NOT catalyzed by the pyruvate dehydrogenase complex?

Correct Answer
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Exam 16: The Citric Acid Cycle

Why is flux through the citric acid low in the resting state?

Correct AnswerverifiedShow Answer

Describe the enzymes, cofactors, intermediates, and products the pyruvate dehydrogenase complex.

Correct AnswerAnswered by ExamLex AIThe pyruvate dehydrogenase complex is a ...View AnswerShow Answer

Which statement is NOT true of the reaction catalyzed by the pyruvate dehydrogenase complex?

Correct AnswerverifiedShow Answer

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?

Correct AnswerverifiedShow Answer

There are few, if any, humans with defects in the enzymes of the citric acid cycle. Explain this observation in terms of the role of the citric acid cycle.

Correct AnswerAnswered by ExamLex AIThe citric acid cycle, also known as the...View AnswerShow Answer

Which high-energy bond is associated with the succinyl-CoA synthetase reaction?

Correct AnswerverifiedShow Answer

The oxidative step of the citric acid cycle that is NOT linked to the reduction of NAD+ is the reaction catalyzed by:

Correct AnswerverifiedShow Answer

Correct AnswerAnswered by ExamLex AIThe vitamin that might be deficient in t...View AnswerShow Answer

Which statement is FALSE regarding regulation of the pyruvate dehydrogenase complex?

Correct AnswerverifiedShow Answer

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:

Correct AnswerverifiedShow Answer

Which reaction of the citric acid cycle requires a water molecule?

Correct AnswerverifiedShow Answer

Which vitamin is NOT a precursor for a cofactor in the pyruvate dehydrogenase complex?

Correct AnswerverifiedShow Answer

CO2 is produced in two reactions in the citric acid cycle. For each of these reactions, name and show the structures of reactant and product, name the enzyme, and show how any cofactors participate.

Correct AnswerAnswered by ExamLex AIThe first reaction in the citric acid cy...View AnswerShow Answer

Which intermediate of the citric acid cycle is prochiral?

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Arsenic inhibits the pyruvate dehydrogenase complex by inactivating the dihydrolipoamide component of dihydrolipoyl transacetylase. Which enzyme is also MOST likely to be inhibited by arsenic?

Correct AnswerverifiedShow Answer

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?

Correct AnswerverifiedShow Answer

Which enzymatic activity would be decreased by thiamine deficiency?

Correct AnswerverifiedShow Answer

The glyoxylate cycle in germinating seeds is a pathway that has some similarity to the citric acid cycle. It uses the carbon-based products from the catabolism of fatty acids as the precursors for gluconeogenesis. How can the glyoxylate cycle accomplish this?

Correct AnswerverifiedShow Answer

Two of the steps in the oxidative decarboxylation of pyruvate to acetyl-CoA do not involve the three carbons of pyruvate, yet are essential to the operation of the pyruvate dehydrogenase complex. Explain.

Correct AnswerAnswered by ExamLex AIThe two steps in the oxidative decarboxy...View AnswerShow Answer

Which step is NOT catalyzed by the pyruvate dehydrogenase complex?

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Correct Answer
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Correct Answer
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The pyruvate dehydrogenase complex is a ...
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Correct Answer
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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?

Correct Answer
verified

Correct Answer
Answered by ExamLex AI
The citric acid cycle, also known as the...
View Answer

Correct Answer
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The oxidative step of the citric acid cycle that is NOT linked to the reduction of NAD⁺ is the reaction catalyzed by:

Correct Answer
verified

Correct Answer
Answered by ExamLex AI
The vitamin that might be deficient in t...
View Answer

Correct Answer
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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:

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

CO₂ is produced in two reactions in the citric acid cycle. For each of these reactions, name and show the structures of reactant and product, name the enzyme, and show how any cofactors participate.

Correct Answer
Answered by ExamLex AI
The first reaction in the citric acid cy...
View Answer

Correct Answer
verified

Correct Answer
verified

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?

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
Answered by ExamLex AI
The two steps in the oxidative decarboxy...
View Answer

Correct Answer
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