Question 1

How would a high NADH to NAD+ ratio be expected to affect the pyruvate dehydrogenase reaction?

Accepted Answer

A)  The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an increase in 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 increase in 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 2

Which reaction in the citrate cycle produces NADH?

Accepted Answer

A)  4 
B)  5 
C)  6 
D)  7 
A)  4 
B)  5 
C)  6 
D)  7

Question 3

Predict what happens to citrate in a cell when ATP and NADH concentrations are high.

Accepted Answer

The citrate cycle is inhibited under the

Question 4

ATP regulates the citrate cycle but is not found as a direct product of any of the reactions.Explain how ATP regulates the cycle and identify the enzymes that ATP regulates.

Accepted Answer

ATP is an example of feedback inhibition

Question 5

Which reaction in the citrate cycle produces FADH2?

Accepted Answer

A)  3 
B)  4 
C)  5 
D)  6 
A)  3 
B)  4 
C)  5 
D)  6

Question 6

Compare the two roles of lipoic acid in the pyruvate dehydrogenase reaction.

Accepted Answer

Lipoic acid provides a reactiv

Question 7

Which of the following is a reactant in the net reaction of the citrate cycle?

Accepted Answer

A)  CO2 
B)  H2O 
C)  GTP 
D)  CoA 
A)  CO2 
B)  H2O 
C)  GTP 
D)  CoA

Question 8

Calculate the    of a coupled redox reaction with O2 and ferredoxin (Fe2+)using the table below.

Accepted Answer

A)  -1.25 
B)  -0.39 
C)  0.39 
D)  1.25 
A)  -1.25 
B)  -0.39 
C)  0.39 
D)  1.25

Question 9

The regulatory mechanism in the citrate cycle involving the NADH to NAD+ ratio is considered to be an example of regulation by

Accepted Answer

A)  pH and protonation state. 
B)  product inhibition. 
C)  covalent modification. 
D)  pH and enzyme conformation. 
A)  pH and protonation state. 
B)  product inhibition. 
C)  covalent modification. 
D)  pH and enzyme conformation.

Question 10

The reaction catalyzed by __________is the most endergonic reaction in the citrate cycle.

Accepted Answer

A)  fumarase 
B)  succinate dehydrogenase 
C)  malate dehydrogenase 
D)  aconitase 
A)  fumarase 
B)  succinate dehydrogenase 
C)  malate dehydrogenase 
D)  aconitase

Question 11

An in vitro study shows that citrate synthase is inhibited in the citrate cycle.What is a possible explanation for this inhibition?

Accepted Answer

A)  high levels of ADP 
B)  low levels of succinyl-CoA 
C)  high levels of NADH 
D)  high levels of AMP 
A)  high levels of ADP 
B)  low levels of succinyl-CoA 
C)  high levels of NADH 
D)  high levels of AMP

Question 12

Identify the E1 subunit in the reaction schematic of the pyruvate dehydrogenase reaction below.

Accepted Answer

A)  pyruvate dehydrogenase 
B)  dihydrolipoyl dehydrogenase 
C)  dihydrolipopyl acetyltransferase 
D)  flavin adenine dinucleotide 
A)  pyruvate dehydrogenase 
B)  dihydrolipoyl dehydrogenase 
C)  dihydrolipopyl acetyltransferase 
D)  flavin adenine dinucleotide

Question 13

Classify the reaction that occurs at step 1 in the reaction schematic of the pyruvate dehydrogenase reaction below.

Accepted Answer

A)  isomerization 
B)  addition 
C)  oxidation reduction 
D)  decarboxylation 
A)  isomerization 
B)  addition 
C)  oxidation reduction 
D)  decarboxylation

Question 14

Identify the strongest oxidant in the table below.

Accepted Answer

A)  O2 
B)  oxaloacetate 
C)  pyruvate 
D)  ferredoxin 
A)  O2 
B)  oxaloacetate 
C)  pyruvate 
D)  ferredoxin

Question 15

Compare and contrast the functions of NAD+ and FAD in the citrate cycle.

Accepted Answer

Both NAD⁺and FAD act as coenzymes.They ac

Question 16

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)    -ketoglutarate dehydrogenase 
A)  pyruvate dehydrogenase 
B)  citrate synthase 
C)  isocitrate dehydrogenase 
D)    -ketoglutarate dehydrogenase

Question 17

An in vitro study shows that   -ketoglutarate dehydrogenase is inhibited in the citrate cycle.What is a possible explanation for this inhibition?

Accepted Answer

A)  high levels of ATP 
B)  low levels of Ca2+ 
C)  low levels of NADH 
D)  high levels of ADP 
A)  high levels of ATP 
B)  low levels of Ca2+ 
C)  low levels of NADH 
D)  high levels of ADP

Question 18

An in vitro study shows that isocitrate dehydrogenase is activated in the citrate cycle.What is a possible explanation for the activation?

Accepted Answer

A)  high levels of ATP 
B)  low levels of ATP 
C)  high levels of NADH 
D)  low levels of AMP 
A)  high levels of ATP 
B)  low levels of ATP 
C)  high levels of NADH 
D)  low levels of AMP

Question 19

What enzyme in the citrate cycle is activated by high concentrations of AMP?

Accepted Answer

A)  isocitrate dehydrogenase 
B)    -ketoglutarate dehydrogenase 
C)  citrate synthase 
D)  succinyl-CoA synthetase 
A)  isocitrate dehydrogenase 
B)    -ketoglutarate dehydrogenase 
C)  citrate synthase 
D)  succinyl-CoA synthetase

Question 20

Which reactions in the citrate cycle produce NADH?

Accepted Answer

A)  1, 2, and 4 
B)  3, 4, and 8 
C)  3, 6, and 7 
D)  5, 6, and 8 
A)  1, 2, and 4 
B)  3, 4, and 8 
C)  3, 6, and 7 
D)  5, 6, and 8

Exam 10: The Citrate Cycle

How would a high NADH to NAD+ ratio be expected to affect the pyruvate dehydrogenase reaction?

Which reaction in the citrate cycle produces NADH?

Predict what happens to citrate in a cell when ATP and NADH concentrations are high.

ATP regulates the citrate cycle but is not found as a direct product of any of the reactions.Explain how ATP regulates the cycle and identify the enzymes that ATP regulates.

Which reaction in the citrate cycle produces FADH2?

Compare the two roles of lipoic acid in the pyruvate dehydrogenase reaction.

Which of the following is a reactant in the net reaction of the citrate cycle?

Calculate the of a coupled redox reaction with O2 and ferredoxin (Fe2+)using the table below.

The regulatory mechanism in the citrate cycle involving the NADH to NAD+ ratio is considered to be an example of regulation by

The reaction catalyzed by __________is the most endergonic reaction in the citrate cycle.

An in vitro study shows that citrate synthase is inhibited in the citrate cycle.What is a possible explanation for this inhibition?

Identify the E1 subunit in the reaction schematic of the pyruvate dehydrogenase reaction below.

Classify the reaction that occurs at step 1 in the reaction schematic of the pyruvate dehydrogenase reaction below.

Identify the strongest oxidant in the table below.

Compare and contrast the functions of NAD+ and FAD in the citrate cycle.

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

An in vitro study shows that -ketoglutarate dehydrogenase is inhibited in the citrate cycle.What is a possible explanation for this inhibition?

An in vitro study shows that isocitrate dehydrogenase is activated in the citrate cycle.What is a possible explanation for the activation?

What enzyme in the citrate cycle is activated by high concentrations of AMP?

Which reactions in the citrate cycle produce NADH?

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 a high NADH to NAD⁺ ratio be expected to affect the pyruvate dehydrogenase reaction?

Which reaction in the citrate cycle produces FADH₂?

Calculate the of a coupled redox reaction with O₂ and ferredoxin (Fe²⁺)using the table below.

The regulatory mechanism in the citrate cycle involving the NADH to NAD⁺ ratio is considered to be an example of regulation by

Compare and contrast the functions of NAD⁺and FAD in the citrate cycle.

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