Question 1

Which of the following is not an intermediate of the citric acid cycle?

Accepted Answer

A)  Acetyl-CoA
B)  Citrate
C)  Oxaloacetate
D)  Succinyl-CoA
E)  ( α\alphaα -Ketoglutarate)

Question 2

All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD+ except 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.

Question 3

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:

Accepted Answer

A)  citrate to isocitrate.
B)  fumarate to malate.
C)  malate to oxaloacetate.
D)  succinyl-CoA to succinate.
E)  ( α\alphaα -ketoglutarate to succinyl-CoA.)

Question 4

In mammals,each of the following occurs during the citric acid cycle except:

Accepted Answer

A)  formation of  α\alphaα -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.

Question 5

A function of the glyoxylate cycle,in conjunction with the citric acid cycle,is to accomplish the:

Accepted Answer

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.

Question 6

For the following reaction, Δ\DeltaΔ  G'° = 29.7 kJ/mol. L-Malate + NAD+  →\rightarrow→    oxaloacetate + NADH + H+
The reaction as written:

Accepted Answer

A)  can never occur in a cell.
B)  can only occur in a cell if it is coupled to another reaction for which  Δ\DeltaΔ  G'° 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

Question 7

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 most likely explanation is that the patient has a deficiency of thiamine,without which the cell cannot make thiamine pyrophosphate,the cofactor for pyruvate dehydrogenase.The inability to oxidize pyruvate produced by glycolysis to acetyl-CoA would lead to accumulation of pyruvate in blood and urine.The most direct test for this deficiency is to feed a diet supplemented with thiamine and determine whether urinary pyruvate levels fall.

Question 8

Anaplerotic reactions .

Accepted Answer

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

Question 9

What is the function of FAD in the pyruvate dehydrogenase complex? How is it regenerated?

Accepted Answer

FAD serves as the electron acceptor in the re-oxidation of the cofactor dihydrolipoate.It is converted to FADH₂ by this reaction and is regenerated by the passage of electrons to NAD⁺.

Question 10

The citric acid cycle is frequently described as the major pathway of aerobic catabolism,which means that it is an oxygen-dependent degradative process.However,none of the reactions of the cycle directly involves oxygen as a reactant.Why is the pathway oxygen-dependent?

Accepted Answer

The citric acid cycle produces NADH,whic...

Question 11

The glyoxylate cycle is:

Accepted Answer

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) .

Question 12

At what point in the citric acid cycle do the methyl carbon from acetyl-CoA and the carbonyl carbon from oxaloacetate become chemically equivalent?

Accepted Answer

This happe...

Question 13

Match the cofactor with its function in the citric acid cycle.A given function may be used more than once or not at all.
-

Accepted Answer

(a)-(3)
(b...

Question 14

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 catalyzed by dihydrolipoyl dehydrogenase (E₃)are required to regenerate the oxidized form of lipoate,bound to dihydrolipoyl transacetylase,from the dihydrolipoyl (reduced)form produced in the oxidation of pyruvate.First,FAD is reduced to FADH₂ to reoxidize the dihydrolipoate,then NAD⁺ is reduced to NADH to reoxidize the FADH₂ to complete the reaction.

Question 15

In which reaction of the citric acid cycle does substrate-level phosphorylation occur?

Accepted Answer

Substrate-level phosphorylatio...

Question 16

Entry of acetyl-CoA into the citric acid cycle is decreased when:

Accepted Answer

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.

Question 17

The oxidative decarboxylation of  α\alphaα -ketoglutarate proceeds by means of multistep reactions in which all but one of the following cofactors are required.Which one is not required?

Accepted Answer

A)  ATP
B)  Coenzyme A
C)  Lipoic acid
D)  NAD+ 
E)  Thiamine pyrophosphate

Question 18

Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA?

Accepted Answer

A)  ATP
B)  CoA-SH
C)  FAD
D)  Lipoic acid
E)  NAD+

Question 19

Briefly describe the relationship of the pyruvate dehydrogenase complex reaction to glycolysis and the citric acid cycle.

Accepted Answer

The pyruvate dehydrogenase com...

Question 20

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?

Accepted Answer

A)  Citrate
B)  Fumarate
C)  Isocitrate
D)  Pyruvate
E)  Succinate

Exam 16: The Citric Acid Cycle

Which of the following is not an intermediate of the citric acid cycle?

Correct Answer
verified

All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD⁺ except the reaction catalyzed by:

Correct Answer
verified

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:

Correct Answer
verified

In mammals,each of the following occurs during the citric acid cycle except:

Correct Answer
verified

A function of the glyoxylate cycle,in conjunction with the citric acid cycle,is to accomplish the:

Correct Answer
verified

For the following reaction, $\Delta$ G'° = 29.7 kJ/mol. L-Malate + NAD⁺ $\rightarrow$ oxaloacetate + NADH + H⁺ The reaction as written:

Correct Answer
verified

Anaplerotic reactions .

Correct Answer
verified

What is the function of FAD in the pyruvate dehydrogenase complex? How is it regenerated?

Correct Answer
verified
FAD serves as the electron acceptor in the re-oxidation of the cofactor dihydrolipoate.It is converted to FADH₂ by this reaction and is regenerated by the passage of electrons to NAD⁺.

The citric acid cycle is frequently described as the major pathway of aerobic catabolism,which means that it is an oxygen-dependent degradative process.However,none of the reactions of the cycle directly involves oxygen as a reactant.Why is the pathway oxygen-dependent?

Correct Answer
verified
The citric acid cycle produces NADH,whic...
View Answer

The glyoxylate cycle is:

Correct Answer
verified

At what point in the citric acid cycle do the methyl carbon from acetyl-CoA and the carbonyl carbon from oxaloacetate become chemically equivalent?

Correct Answer
verified
This happe...
View Answer

Match the cofactor with its function in the citric acid cycle.A given function may be used more than once or not at all. -

Correct Answer
verified
(a)-(3)
(b...
View 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.

In which reaction of the citric acid cycle does substrate-level phosphorylation occur?

Correct Answer
verified
Substrate-level phosphorylatio...
View Answer

Entry of acetyl-CoA into the citric acid cycle is decreased when:

Correct Answer
verified

The oxidative decarboxylation of $\alpha$ -ketoglutarate proceeds by means of multistep reactions in which all but one of the following cofactors are required.Which one is not required?

Correct Answer
verified

Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA?

Correct Answer
verified

Briefly describe the relationship of the pyruvate dehydrogenase complex reaction to glycolysis and the citric acid cycle.

Correct Answer
verified
The pyruvate dehydrogenase com...
View Answer

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?

Correct Answer
verified

Exam 16: The Citric Acid Cycle

Which of the following is not an intermediate of the citric acid cycle?

Correct AnswerverifiedShow Answer

All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD+ except the reaction catalyzed by:

Correct AnswerverifiedShow Answer

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:

Correct AnswerverifiedShow Answer

In mammals,each of the following occurs during the citric acid cycle except:

Correct AnswerverifiedShow Answer

A function of the glyoxylate cycle,in conjunction with the citric acid cycle,is to accomplish the:

Correct AnswerverifiedShow Answer

For the following reaction, Δ\DeltaΔ G'° = 29.7 kJ/mol. L-Malate + NAD+ →\rightarrow→ oxaloacetate + NADH + H+ The reaction as written:

Correct AnswerverifiedShow Answer

Anaplerotic reactions .

Correct AnswerverifiedShow Answer

What is the function of FAD in the pyruvate dehydrogenase complex? How is it regenerated?

Correct AnswerverifiedFAD serves as the electron acceptor in the re-oxidation of the cofactor dihydrolipoate.It is converted to FADH2 by this reaction and is regenerated by the passage of electrons to NAD+.

The citric acid cycle is frequently described as the major pathway of aerobic catabolism,which means that it is an oxygen-dependent degradative process.However,none of the reactions of the cycle directly involves oxygen as a reactant.Why is the pathway oxygen-dependent?

Correct AnswerverifiedThe citric acid cycle produces NADH,whic...View AnswerShow Answer

The glyoxylate cycle is:

Correct AnswerverifiedShow Answer

At what point in the citric acid cycle do the methyl carbon from acetyl-CoA and the carbonyl carbon from oxaloacetate become chemically equivalent?

Correct AnswerverifiedThis happe...View AnswerShow Answer

Match the cofactor with its function in the citric acid cycle.A given function may be used more than once or not at all. -

Correct Answerverified(a)-(3)(b...View AnswerShow 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.

In which reaction of the citric acid cycle does substrate-level phosphorylation occur?

Correct AnswerverifiedSubstrate-level phosphorylatio...View AnswerShow Answer

Entry of acetyl-CoA into the citric acid cycle is decreased when:

Correct AnswerverifiedShow Answer

The oxidative decarboxylation of α\alphaα -ketoglutarate proceeds by means of multistep reactions in which all but one of the following cofactors are required.Which one is not required?

Correct AnswerverifiedShow Answer

Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA?

Correct AnswerverifiedShow Answer

Briefly describe the relationship of the pyruvate dehydrogenase complex reaction to glycolysis and the citric acid cycle.

Correct AnswerverifiedThe pyruvate dehydrogenase com...View AnswerShow Answer

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?

Correct AnswerverifiedShow Answer

Correct Answer
verified

All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD⁺ except the reaction catalyzed by:

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

For the following reaction, $\Delta$ G'° = 29.7 kJ/mol. L-Malate + NAD⁺ $\rightarrow$ oxaloacetate + NADH + H⁺ The reaction as written:

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
FAD serves as the electron acceptor in the re-oxidation of the cofactor dihydrolipoate.It is converted to FADH₂ by this reaction and is regenerated by the passage of electrons to NAD⁺.

Correct Answer
verified
The citric acid cycle produces NADH,whic...
View Answer

Correct Answer
verified

Correct Answer
verified
This happe...
View Answer

Correct Answer
verified
(a)-(3)
(b...
View Answer

Correct Answer
verified
Substrate-level phosphorylatio...
View Answer

Correct Answer
verified

The oxidative decarboxylation of $\alpha$ -ketoglutarate proceeds by means of multistep reactions in which all but one of the following cofactors are required.Which one is not required?

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
The pyruvate dehydrogenase com...
View Answer

Correct Answer
verified