Question 1

Which of the following coenzymes is required for the decarboxylation of pyruvate by the pyruvate dehydrogenase complex?

Accepted Answer

A) thiamine pyrophosphate 
B) coenzyme A 
C) lipoic acid 
D) NAD+ 
E) FAD 
A) thiamine pyrophosphate 
B) coenzyme A 
C) lipoic acid 
D) NAD+ 
E) FAD A

Question 2

Draw the enzyme-bound intermediate of the following reaction clearly showing proper stereochemistry:

Accepted Answer

The answer of Draw the enzyme-bound intermediate of the following...

Question 3

Which oxidation reaction requires the coenzyme FAD because it involves oxidation of a carbon-carbon single bond to a double bond?

Accepted Answer

A) oxidation of isocitrate to $\alpha$-ketoglutarate 
B) oxidation of $\alpha$-ketoglutarate to succinyl-CoA 
C) oxidation of succinate to fumarate 
D) oxidation of malate to oxaloacetate 
E) oxidation of pyruvate to acetyl-CoA 
A) oxidation of isocitrate to $\alpha$-ketoglutarate 
B) oxidation of $\alpha$-ketoglutarate to succinyl-CoA 
C) oxidation of succinate to fumarate 
D) oxidation of malate to oxaloacetate 
E) oxidation of pyruvate to acetyl-CoA C

Question 4

In the citric acid cycle, acetyl-CoA reacts with ________ to produce _________.

Accepted Answer

A) fumarate; $\alpha$-ketoglutarate 
B) oxaloacetate; citrate 
C) citrate; isocitrate 
D) succinyl-CoA; oxaloacetate 
E) malate; cis-aconitate 
A) fumarate; $\alpha$-ketoglutarate 
B) oxaloacetate; citrate 
C) citrate; isocitrate 
D) succinyl-CoA; oxaloacetate 
E) malate; cis-aconitate

Question 5

Arsenic poisoning by either arsenite or organic arsenical agents work by binding to dithiol compounds such as _________ meaning that in addition to inactivation of pyruvate dehydrogenase, the citric acid cycle enzyme _________ would be inactivated.

Accepted Answer

A) cysteine; aconitase 
B) coenzyme A; $\alpha$-ketoglutarate dehydrogenase 
C) coenzyme A; citrate synthase 
D) thiamine pyrophosphate; isocitrate dehydrogenase 
E) lipoic acid; $\alpha$-ketoglutarate dehydrogenase 
A) cysteine; aconitase 
B) coenzyme A; $\alpha$-ketoglutarate dehydrogenase 
C) coenzyme A; citrate synthase 
D) thiamine pyrophosphate; isocitrate dehydrogenase 
E) lipoic acid; $\alpha$-ketoglutarate dehydrogenase

Question 6

The oxidation reactions that convert pyruvate to CO2 are specifically catalyzed by ______ enzymes.

Accepted Answer

A) oxygenase 
B) oxidase 
C) decarboxylase 
D) dehydrogenase 
E) none of the above 
A) oxygenase 
B) oxidase 
C) decarboxylase 
D) dehydrogenase 
E) none of the above

Question 7

Which of the following enzymes of the pyruvate dehydrogenase complex is responsible for the oxidation of the hydroxyethyl group from pyruvate decarboxylation to an acetyl group?

Accepted Answer

A) pyruvate dehydrogenase 
B) dihydrolipoamide transacetylase 
C) dihydrolipoamide dehydrogenase 
D) pyruvate dehydrogenase kinase 
E) pyruvate dehydrogenase phosphatase 
A) pyruvate dehydrogenase 
B) dihydrolipoamide transacetylase 
C) dihydrolipoamide dehydrogenase 
D) pyruvate dehydrogenase kinase 
E) pyruvate dehydrogenase phosphatase

Question 8

For each molecule of acetyl-CoA that enters the citric acid cycle, which of the following best represents the net products of the cycle?

Accepted Answer

A) 2 CO2, 2 NADH, 2 FADH2, 1 GTP, 1 oxaloacetate 
B) 1 CO2, 3 NADH, 1 FADH2, 2 GTP, 1 oxaloacetate 
C) 2 CO2, 3 NADH, 1 FADH2, 1 GTP, 0 oxaloacetate 
D) 1 CO2, 2 NADH, 1 FADH2, 2 GTP, 0 oxaloacetate 
E) 2 CO2, 3 NADH, 1 FADH2, 1 GTP, 1 oxaloacetate 
A) 2 CO2, 2 NADH, 2 FADH2, 1 GTP, 1 oxaloacetate 
B) 1 CO2, 3 NADH, 1 FADH2, 2 GTP, 1 oxaloacetate 
C) 2 CO2, 3 NADH, 1 FADH2, 1 GTP, 0 oxaloacetate 
D) 1 CO2, 2 NADH, 1 FADH2, 2 GTP, 0 oxaloacetate 
E) 2 CO2, 3 NADH, 1 FADH2, 1 GTP, 1 oxaloacetate

Question 9

Which of the following molecules is correctly paired with the enzyme that can convert it to oxaloacetate to replenish the citric acid cycle when other intermediates are removed?

Accepted Answer

A) aspartate: aspartate deaminase 
B) pyruvate: malic enzyme 
C) phosphoenolpyruvate: PEP carboxylase 
D) glutamate: glutamate transaminase 
E) none of the above 
A) aspartate: aspartate deaminase 
B) pyruvate: malic enzyme 
C) phosphoenolpyruvate: PEP carboxylase 
D) glutamate: glutamate transaminase 
E) none of the above

Question 10

__________ activates __________, thereby inhibiting pyruvate dehydrogenase.

Accepted Answer

A) NADH; pyruvate dehydrogenase phosphatase 
B) Ca2+; pyruvate dehydrogenase phosphatase 
C) NAD+; pyruvate dehydrogenase kinase 
D) ATP; pyruvate dehydrogenase kinase 
E) pyruvate; pyruvate dehydrogenase kinase 
A) NADH; pyruvate dehydrogenase phosphatase 
B) Ca2+; pyruvate dehydrogenase phosphatase 
C) NAD+; pyruvate dehydrogenase kinase 
D) ATP; pyruvate dehydrogenase kinase 
E) pyruvate; pyruvate dehydrogenase kinase

Question 11

The complete oxidation of the acetyl group that enters the citric acid cycle yields _____ electrons from the methyl carbon and ____ electrons from the carbonyl carbon.

Accepted Answer

A) 4; 2 
B) 6; 2. 
C) 6; 4 
D) 8; 2 
E) 8; 2. 
A) 4; 2 
B) 6; 2. 
C) 6; 4 
D) 8; 2 
E) 8; 2.

Question 12

What role does the coenzyme A portion of acetyl-CoA play in the reaction catalyzed by citrate synthase?

Accepted Answer

A) the CoA group causes the enzyme to close around the substrates, enabling catalysis 
B) lack of resonance in the thioester makes the methyl carbon of the acetyl group more acidic, allowing proton abstraction to readily occur 
C) CoA makes the carbonyl carbon highly susceptible to nucleophilic attack 
D) hydrolysis of the thioester makes the reaction essentially irreversible 
E) all of the above 
A) the CoA group causes the enzyme to close around the substrates, enabling catalysis 
B) lack of resonance in the thioester makes the methyl carbon of the acetyl group more acidic, allowing proton abstraction to readily occur 
C) CoA makes the carbonyl carbon highly susceptible to nucleophilic attack 
D) hydrolysis of the thioester makes the reaction essentially irreversible 
E) all of the above

Question 13

Which of the following is an enzyme-bound intermediate in the reaction catalyzed by succinyl-CoA synthetase?

Accepted Answer

A) succinyl phosphate 
B) glutamyl-CoA 
C) N-phosphohistidine 
D) N-ADP-histidine 
E) none of the above 
A) succinyl phosphate 
B) glutamyl-CoA 
C) N-phosphohistidine 
D) N-ADP-histidine 
E) none of the above

Question 14

The most common reactions of acetyl acetyl-CoA are with a nucleophile or with a base. Show the reactions of acetyl CoA with the generic base and the generic nucleophile:

Accepted Answer

The answer of The most common reactions of acetyl acetyl-CoA...

Question 15

The conversion of citrate to isocitrate by the enzyme aconitase is best described as ______ reaction consisting of a ________ followed by a ________.

Accepted Answer

A) isomerization; oxidation; reduction 
B) isomerization; hydration; dehydration 
C) isomerization; dehydration; hydration 
D) group transfer; dehydroxylation; hydroxylation 
E) group transfer; hydroxylation; dehydroxylation 
A) isomerization; oxidation; reduction 
B) isomerization; hydration; dehydration 
C) isomerization; dehydration; hydration 
D) group transfer; dehydroxylation; hydroxylation 
E) group transfer; hydroxylation; dehydroxylation

Question 16

The two reactions of the citric acid cycle where CO2 is produced are catalyzed by _________ and _________

Accepted Answer

A) isocitrate dehydrogenase; $\alpha$-ketoglutarate dehydrogenase 
B) isocitrate dehydrogenase; malate dehydrogenase 
C) $\alpha$-ketoglutarate dehydrogenase; succinate dehydrogenase 
D) $\alpha$-ketoglutarate dehydrogenase; malate dehydrogenase 
E) succinate dehydrogenase; malate dehydrogenase 
A) isocitrate dehydrogenase; $\alpha$-ketoglutarate dehydrogenase 
B) isocitrate dehydrogenase; malate dehydrogenase 
C) $\alpha$-ketoglutarate dehydrogenase; succinate dehydrogenase 
D) $\alpha$-ketoglutarate dehydrogenase; malate dehydrogenase 
E) succinate dehydrogenase; malate dehydrogenase

Question 17

The reaction catalyzed by malate synthase is shown below. Which citric acid cycle enzyme would have a mechanism most similar to malate synthase?

Accepted Answer

A) malate dehydrogenase 
B) citrate synthase 
C) fumarase 
D) succinyl-CoA synthetase 
E) none of the above 
A) malate dehydrogenase 
B) citrate synthase 
C) fumarase 
D) succinyl-CoA synthetase 
E) none of the above

Question 18

Which of the following is an equilibrium-controlled reaction of the citric acid cycle?

Accepted Answer

A) citrate synthase 
B) isocitrate dehydrogenase 
C) $\alpha$-ketoglutarate dehydrogenase 
D) succinate dehydrogenase 
E) all of the above 
A) citrate synthase 
B) isocitrate dehydrogenase 
C) $\alpha$-ketoglutarate dehydrogenase 
D) succinate dehydrogenase 
E) all of the above

Question 19

Which of the following reactions is commonly used to replenish intermediates of the citric acid cycle?

Accepted Answer

A) citrate $\rarr$oxaloacetate + acetyl CoA 
B) oxaloacetate $\rarr$ aspartate 
C) glutamate $\rarr$ $\alpha$-ketoglutarate 
D) malate $\rarr$ pyruvate 
E) all of the above 
A) citrate $\rarr$oxaloacetate + acetyl CoA 
B) oxaloacetate $\rarr$ aspartate 
C) glutamate $\rarr$ $\alpha$-ketoglutarate 
D) malate $\rarr$ pyruvate 
E) all of the above

Question 20

Which of the following is an inhibitor of citrate synthase, isocitrate dehydrogenase, and $\alpha$-ketoglutarate dehydrogenase?

Accepted Answer

A) NADH 
B) succinyl-CoA 
C) ATP 
D) acetyl-CoA 
E) none of the above 
A) NADH 
B) succinyl-CoA 
C) ATP 
D) acetyl-CoA 
E) none of the above

Exam 14: Citric Acid Cycle and Glyoxylate Cycle

Which of the following coenzymes is required for the decarboxylation of pyruvate by the pyruvate dehydrogenase complex?

Draw the enzyme-bound intermediate of the following reaction clearly showing proper stereochemistry:

Which oxidation reaction requires the coenzyme FAD because it involves oxidation of a carbon-carbon single bond to a double bond?

In the citric acid cycle, acetyl-CoA reacts with ________ to produce _________.

Arsenic poisoning by either arsenite or organic arsenical agents work by binding to dithiol compounds such as _________ meaning that in addition to inactivation of pyruvate dehydrogenase, the citric acid cycle enzyme _________ would be inactivated.

The oxidation reactions that convert pyruvate to CO2 are specifically catalyzed by ______ enzymes.

Which of the following enzymes of the pyruvate dehydrogenase complex is responsible for the oxidation of the hydroxyethyl group from pyruvate decarboxylation to an acetyl group?

For each molecule of acetyl-CoA that enters the citric acid cycle, which of the following best represents the net products of the cycle?

Which of the following molecules is correctly paired with the enzyme that can convert it to oxaloacetate to replenish the citric acid cycle when other intermediates are removed?

__________ activates __________, thereby inhibiting pyruvate dehydrogenase.

The complete oxidation of the acetyl group that enters the citric acid cycle yields _____ electrons from the methyl carbon and ____ electrons from the carbonyl carbon.

What role does the coenzyme A portion of acetyl-CoA play in the reaction catalyzed by citrate synthase?

Which of the following is an enzyme-bound intermediate in the reaction catalyzed by succinyl-CoA synthetase?

The most common reactions of acetyl acetyl-CoA are with a nucleophile or with a base. Show the reactions of acetyl CoA with the generic base and the generic nucleophile:

The conversion of citrate to isocitrate by the enzyme aconitase is best described as ______ reaction consisting of a ________ followed by a ________.

The two reactions of the citric acid cycle where CO2 is produced are catalyzed by _________ and _________

The reaction catalyzed by malate synthase is shown below. Which citric acid cycle enzyme would have a mechanism most similar to malate synthase?

Which of the following is an equilibrium-controlled reaction of the citric acid cycle?

Which of the following reactions is commonly used to replenish intermediates of the citric acid cycle?

Which of the following is an inhibitor of citrate synthase, isocitrate dehydrogenase, and α\alphaα -ketoglutarate dehydrogenase?

The Scope of Biochemistry

The Matrix of Life: Weak Interactions in an Aqueous Environment

The Energetics of Life

Nucleic Acids

Introduction to Proteins: the Primary Level of Protein Structure

The Three-Dimensional Structure of Proteins

Protein Function and Evolution

Contractile Proteins and Molecular Motors

Carbohydrates: Sugars, Saccharides, Glycans

Lipids, Membranes and Cellular Transport

Enzymes: Biological Catalysts

Chemical Logic of Metabolism

Carbohydrate Metabolism: Glycolysis, Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Electron Transport, Oxidative Phosphorylation, and Oxygen Metabolism

Photosynthesis

Lipid Metabolism I: Fatty Acids, Triacylglycerols, and Lipoproteins

Interorgan and Intracellular Coordination of Energy Metabolism in Vertebrates

Lipid Metabolism Ii: Membrane Lipids, Steroids, Isoprenoids, and Eicosanoids

Metabolism of Nitrogenous Compounds I: Principles of Biosynthesis, Utilization, and Turnover

Metabolism of Nitogenous Compounds II: Amino Acids, Porphyrins, and Neurotransmitters

Nucleotide Metabolism

Mechanisms of Signal Transduction

Genes, Genomes and Chromosomes

DNA Replication

DNA Restructuring: Repair, Recombination, Rearrangement, Amplification

Information Readout: Transcription and Post-Transcriptional Processing

Information Decoding: Translation and Post-Translational Protein Processing

Regulation of Gene Expression

Filters

In the citric acid cycle, acetyl-CoA reacts with to produce _.

Arsenic poisoning by either arsenite or organic arsenical agents work by binding to dithiol compounds such as _ meaning that in addition to inactivation of pyruvate dehydrogenase, the citric acid cycle enzyme _ would be inactivated.

The oxidation reactions that convert pyruvate to CO₂ are specifically catalyzed by ______ enzymes.

activates , thereby inhibiting pyruvate dehydrogenase.

The complete oxidation of the acetyl group that enters the citric acid cycle yields _ electrons from the methyl carbon and electrons from the carbonyl carbon.

The conversion of citrate to isocitrate by the enzyme aconitase is best described as reaction consisting of a followed by a __.

The two reactions of the citric acid cycle where CO₂ is produced are catalyzed by _ and _

Which of the following is an inhibitor of citrate synthase, isocitrate dehydrogenase, and $\alpha$ -ketoglutarate dehydrogenase?