Question 1

Which molecules function as electron acceptors in the citrate cycle?

Accepted Answer

A)  NAD+, FAD 
B)  NADH, FADH2 
C)  GDP, ADP 
D)  GTP, ATP 
A)  NAD+, FAD 
B)  NADH, FADH2 
C)  GDP, ADP 
D)  GTP, ATP

Question 2

How would an increase in Ca2+ be expected to affect the pyruvate dehydrogenase reaction?

Accepted Answer

A)  The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity. 
B)  The last step of the pyruvate dehydrogenase reaction is blocked, resulting in a decrease in activity. 
C)  The E1 subunit is phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase decreases. 
D)  The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate. 
A)  The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity. 
B)  The last step of the pyruvate dehydrogenase reaction is blocked, resulting in a decrease in activity. 
C)  The E1 subunit is phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase decreases. 
D)  The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate.

Question 3

How many ATP are produced from two turns of the citrate cycle?

Accepted Answer

A)  9 
B)  10 
C)  18 
D)  20 
A)  9 
B)  10 
C)  18 
D)  20

Question 4

Predict the fate of acetyl-CoA and oxaloacetate when the citrate cycle is inhibited.

Accepted Answer

Acetyl Co-A is used in the cytosol for c

Question 5

Which coenzyme in the citrate cycle is affected by arsenic?

Accepted Answer

A)  coenzyme A 
B)  thiamine pyrophosphate 
C)  dihydrolipopyl acetyltransferase 
D)  flavin adenine dinucleotide 
A)  coenzyme A 
B)  thiamine pyrophosphate 
C)  dihydrolipopyl acetyltransferase 
D)  flavin adenine dinucleotide

Question 6

When the citrate cycle is inhibited, which two metabolites are exported to the cytosol for fatty acid and cholesterol synthesis?

Accepted Answer

A)  "malate and succinyl-CoA" 
B)  "succinyl-CoA and $\alpha$-ketoglutarate" 
C)  "$\alpha$-ketoglutarate and citrate" 
D)  "citrate and malate" 
A)  "malate and succinyl-CoA" 
B)  "succinyl-CoA and $\alpha$-ketoglutarate" 
C)  "$\alpha$-ketoglutarate and citrate" 
D)  "citrate and malate"

Question 7

Which two enzymes in the citrate cycle are affected by arsenic poisoning?

Accepted Answer

A)  pyruvate dehydrogenase and succinate dehydrogenase 
B)  pyruvate dehydrogenase and $\alpha$-ketoglutarate dehydrogenase 
C)  malate dehydrogenase and succinate dehydrogenase 
D)  malate dehydrogenase and $\alpha$-ketoglutarate dehydrogenase 
A)  pyruvate dehydrogenase and succinate dehydrogenase 
B)  pyruvate dehydrogenase and $\alpha$-ketoglutarate dehydrogenase 
C)  malate dehydrogenase and succinate dehydrogenase 
D)  malate dehydrogenase and $\alpha$-ketoglutarate dehydrogenase

Question 8

The poison compound 1080 converts fluoroacetate to fluorocitrate. Which enzyme in the citrate cycle is inhibited by this poison?

Accepted Answer

A)  "aconitase" 
B)  "citrate synthase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase" 
A)  "aconitase" 
B)  "citrate synthase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase"

Question 9

How would an increased level of acetyl-CoA be expected to affect the pyruvate dehydrogenase reaction?

Accepted Answer

A)  The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity. 
B)  The last step of the pyruvate dehydrogenase reaction would be blocked, resulting in a decrease in activity. 
C)  The E1 subunit would be phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase would decrease. 
D)  The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate. 
A)  The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity. 
B)  The last step of the pyruvate dehydrogenase reaction would be blocked, resulting in a decrease in activity. 
C)  The E1 subunit would be phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase would decrease. 
D)  The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate.

Question 10

The reaction catalyzed by __________ is the most exergonic reaction in the citrate cycle.

Accepted Answer

A)  "citrate synthase" 
B)  "fumarase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase" 
A)  "citrate synthase" 
B)  "fumarase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase"

Question 11

A high concentration of which molecule would inhibit citrate synthase in the citrate cycle?

Accepted Answer

A)  AMP 
B)  ADP 
C)  NAD+ 
D)  ATP 
A)  AMP 
B)  ADP 
C)  NAD+ 
D)  ATP

Question 12

Use the figure below to answer the following questions.
   A. The electrochemical cell shown here is measuring the reduction potential of Fe2+/Fe3+ using a reference hydrogen half reaction. Write each half reaction on the figure and show the flow of electrons.
B. Do these oxidants have a higher or lower affinity for electrons compared with H+? Explain how you know this using information from the experiment.

Accepted Answer

A. The reference hydrogen half reaction

Question 13

Which enzyme of the citrate cycle catalyzes the oxidative decarboxylation reaction that produces CO2, NADH, and succinyl-CoA?

Accepted Answer

A)  "pyruvate dehydrogenase" 
B)  "citrate synthase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase" 
A)  "pyruvate dehydrogenase" 
B)  "citrate synthase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase"

Question 14

How is the pyruvate dehydrogenase reaction regulated?

Accepted Answer

A)  pH and enzyme conformation 
B)  pH and the protonation state of the active site 
C)  allosteric control and covalent modification 
D)  product inhibition 
A)  pH and enzyme conformation 
B)  pH and the protonation state of the active site 
C)  allosteric control and covalent modification 
D)  product inhibition

Question 15

What is the fate of oxaloacetate when it is not used in the citrate cycle?

Accepted Answer

A)  cholesterol synthesis 
B)  heme synthesis 
C)  amino acid synthesis 
D)  gluconeogenesis 
A)  cholesterol synthesis 
B)  heme synthesis 
C)  amino acid synthesis 
D)  gluconeogenesis

Question 16

Calculate the $\Delta$G$\degree$'  of a redox reaction of pyruvate and hydrogen under standard conditions using the table below.

Accepted Answer

A)  18.33 kJ/mol 
B)  36.66 kJ/mol 
C)  54.99 kJ/mol 
D)  73.32 kJ/mol 
A)  18.33 kJ/mol 
B)  36.66 kJ/mol 
C)  54.99 kJ/mol 
D)  73.32 kJ/mol

Question 17

Why is the $\Delta$G$\degree$'  of the condensation of oxaloacetate and acetyl-CoA highly favorable?

Accepted Answer

A)  The addition of inorganic phosphate provides energy, resulting in the highly favorable nature of this reaction. 
B)  Allosteric regulations of the reaction cause a release of energy, making the reaction thermodynamically favorable. 
C)  The iron-sulfur cluster in the enzyme reduces the activation energy of the reaction, resulting in the favorable $\Delta$G$\degree$' . 
D)  The hydrolysis of the thioester bond in citryl-CoA results in the highly exergonic reaction. 
A)  The addition of inorganic phosphate provides energy, resulting in the highly favorable nature of this reaction. 
B)  Allosteric regulations of the reaction cause a release of energy, making the reaction thermodynamically favorable. 
C)  The iron-sulfur cluster in the enzyme reduces the activation energy of the reaction, resulting in the favorable $\Delta$G$\degree$' . 
D)  The hydrolysis of the thioester bond in citryl-CoA results in the highly exergonic reaction.

Question 18

Identify the coenzyme that provides a reactive disulfide that participates in the redox reaction in the active site of pyruvate dehydrogenase.

Accepted Answer

A)  NAD+ 
B)  coenzyme A 
C)  lipoamide 
D)  thiamine pyrophosphate 
A)  NAD+ 
B)  coenzyme A 
C)  lipoamide 
D)  thiamine pyrophosphate

Question 19

Describe the fate of NADH and FADH2 produced in the citrate cycle.

Accepted Answer

NADH and FADH₂ enter the electr

Question 20

Which anaplerotic reaction balances the input of oxaloacetate with acetyl-CoA in the citrate cycle by converting pyruvate into oxaloacetate?

Accepted Answer

A)  pyruvate carboxylase 
B)  malate dehydrogenase 
C)  malic enzyme 
D)  pyruvate kinase 
A)  pyruvate carboxylase 
B)  malate dehydrogenase 
C)  malic enzyme 
D)  pyruvate kinase

Exam 10: The Citrate Cycle

Which molecules function as electron acceptors in the citrate cycle?

How would an increase in Ca2+ be expected to affect the pyruvate dehydrogenase reaction?

How many ATP are produced from two turns of the citrate cycle?

Predict the fate of acetyl-CoA and oxaloacetate when the citrate cycle is inhibited.

Which coenzyme in the citrate cycle is affected by arsenic?

When the citrate cycle is inhibited, which two metabolites are exported to the cytosol for fatty acid and cholesterol synthesis?

Which two enzymes in the citrate cycle are affected by arsenic poisoning?

The poison compound 1080 converts fluoroacetate to fluorocitrate. Which enzyme in the citrate cycle is inhibited by this poison?

How would an increased level of acetyl-CoA be expected to affect the pyruvate dehydrogenase reaction?

The reaction catalyzed by __________ is the most exergonic reaction in the citrate cycle.

A high concentration of which molecule would inhibit citrate synthase in the citrate cycle?

Which enzyme of the citrate cycle catalyzes the oxidative decarboxylation reaction that produces CO2, NADH, and succinyl-CoA?

How is the pyruvate dehydrogenase reaction regulated?

What is the fate of oxaloacetate when it is not used in the citrate cycle?

Calculate the Δ\DeltaΔ G °\degree° ' of a redox reaction of pyruvate and hydrogen under standard conditions using the table below.

Why is the Δ\DeltaΔ G °\degree° ' of the condensation of oxaloacetate and acetyl-CoA highly favorable?

Identify the coenzyme that provides a reactive disulfide that participates in the redox reaction in the active site of pyruvate dehydrogenase.

Describe the fate of NADH and FADH2 produced in the citrate cycle.

Which anaplerotic reaction balances the input of oxaloacetate with acetyl-CoA in the citrate cycle by converting pyruvate into oxaloacetate?

Principles of Biochemistry

Physical Biochemistry: Energy Conversion, Water, and Membranes

Nucleic Acid Structure and Function

Protein Structure

Methods in Protein Biochemistry

Protein Function

Enzyme Mechanisms

Cell Signaling Systems

Glycolysis: a Paradigm of Metabolic Regulation

Oxidative Phosphorylation

Photosynthesis

Carbohydrate Structure and Function

Carbohydrate Metabolism

Lipid Structure and Function

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Metabolic Integration

DNA Replication, Repair, and Recombination

RNA Synthesis, Processing, and Gene Silencing

Protein Synthesis, Posttranslational Modification, and Transport

Gene Regulation

Filters

How would an increase in Ca²⁺be expected to affect the pyruvate dehydrogenase reaction?

Which enzyme of the citrate cycle catalyzes the oxidative decarboxylation reaction that produces CO₂, NADH, and succinyl-CoA?

Calculate the $\Delta$ G $\degree$ ^' of a redox reaction of pyruvate and hydrogen under standard conditions using the table below. $Calculate the \Delta G \degree <sup>'</sup> <sup> </sup>of a redox reaction of pyruvate and hydrogen under standard conditions using the table below.$

Why is the $\Delta$ G $\degree$ ^' of the condensation of oxaloacetate and acetyl-CoA highly favorable?

Describe the fate of NADH and FADH₂ produced in the citrate cycle.