Question 1

Which statement is FALSE with respect to the pyruvate dehydrogenase complex?

Accepted Answer

A)  It is located in the mitochondrial matrix. 
B)  Its activity is increased in the presence of Ca2+ ions in skeletal muscle. 
C)  Its activity is increased in the presence of coenzyme A and ADP. 
D)  The proximity of the catalytic enzymes in the cluster slows down the overall rate. 
E)  All of the statements are false.

Question 2

Which statement about the oxidative decarboxylation of pyruvate in aerobic conditions in animal cells is CORRECT?

Accepted Answer

A)  One of the products of the reactions of the pyruvate dehydrogenase complex is a thioester of acetate. 
B)  The methyl (-CH3) group is eliminated as CO2. 
C)  The process occurs in the cytosolic compartment of the cell. 
D)  The pyruvate dehydrogenase complex uses all of the following as cofactors: NAD+, lipoic acid, pyridoxal phosphate (PLP), and FAD. 
E)  The reaction is so important to energy production that pyruvate dehydrogenase operates at full speed under all conditions.

Question 3

Which enzyme catalyzes a reversible reaction under normal cellular conditions?

Accepted Answer

A) $\alpha$-ketoglutarate dehydrogenase 
B)  isocitrate dehydrogenase 
C)  succinate dehydrogenase 
D)  pyruvate dehydrogenase 
E)  None of the answers is correct.

Question 4

Germinating plant seeds can convert stored fatty acids into oxaloacetate and a variety of carbohydrates. Animals cannot synthesize significant quantities of oxaloacetate or glucose from fatty acids. What accounts for this difference?

Accepted Answer

The answer of Germinating plant seeds can convert stored fatty...

Question 5

The oxidative decarboxylation of $\alpha$-ketoglutarate proceeds by means of multistep reactions. Which cofactor is NOT required?

Accepted Answer

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

Question 6

Which statement is FALSE regarding the glyoxylate cycle?

Accepted Answer

A)  The glyoxylate cycle utilizes three of the eight enzymes associated with the citric acid cycle. 
B)  In the glyoxylate cycle, the two decarboxylation reactions of the citric acid cycle are bypassed, allowing for the net synthesis of two succinate molecules. 
C)  The glyoxylate cycle is an anabolic pathway occurring in plants and certain microorganisms. 
D)  Because mammals lack the glyoxylate cycle, they cannot convert acetate from the oxidation of fatty acids to glucose. 
E)  The glyoxylate cycle allows plants to use acetate as a source of carbon and as a source of energy.

Question 7

Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA?

Accepted Answer

A)  biotin, FAD, and TPP 
B)  biotin, NAD+, and FAD 
C)  NAD+, biotin, and TPP 
D)  pyridoxal phosphate, FAD, and lipoic acid 
E)  TPP, lipoic acid, and NAD+

Question 8

For the following reaction, $\Delta$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$\Delta$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 9

When is the consumption of acetyl-CoA by the citric acid cycle is decreased?

Accepted Answer

A)  when the concentration of NAD+ is high 
B)  when the concentration of oxaloacetate is high 
C)  when NADH is rapidly reoxidized via the electron transport chain 
D)  when the mitochondrial ATP synthase is inactive 
E)  when the concentrations of NAD+ and oxaloacetate are both high

Question 10

Thyroxine is a competitive inhibitor of malate dehydrogenase. If thyroxine is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which compound would you expect to decrease in concentration FIRST?

Accepted Answer

A)  citrate 
B)  fumarate 
C)  oxaloacetate 
D)  pyruvate 
E)  malate

Question 11

Succinate can be synthesized from pyruvate via two distinct pathways that have no enzyme in common. What are the energy conditions of each pathway?

Accepted Answer

The answer of Succinate can be synthesized from pyruvate via...

Question 12

The citric acid cycle has an important anabolic function by:

Accepted Answer

A)  allowing for the conversion of certain carbon atoms from even-chain fatty acids into glucose. 
B)  producing lactate for gluconeogenesis. 
C)  providing metabolites for the synthesis of cholesterol, amino acids and glucose. 
D)  completing the oxidation of acetyl-CoA and storing electrons in the form of NADH. 
E)  All the answers are correct.

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. Cofactor Function (a) NAD⁺/NADH (1) carries O₂ (b) FAD/FADH₂ (2) carries small carbon-containing molecules (c) CoA (3) carries e^- (d) thiamine (4) carries small nitrogen-containing molecules (e) biotin

Accepted Answer

The answer of Match the cofactor with its function in...

Question 14

Which enzyme in the citric acid cycle has a standard free energy that is large and positive?

Accepted Answer

A)  malate dehydrogenase 
B)  citrate synthase 
C)  succinyl-CoA synthetase 
D)  fumarase 
E)  No enzyme in the CAC has a positive $\Delta$G'°.

Question 15

Although ADP is not directly involved in the isocitrate dehydrogenase reaction, the activity of this enzyme is dependent on the concentration of ADP in the matrix. Briefly explain how.

Accepted Answer

The answer of Although ADP is not directly involved in...

Question 16

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)  $\alpha$-ketoglutarate to succinyl-CoA.

Question 17

Why is the citric acid cycle considered to be part of aerobic metabolism, even though oxygen is not a substrate in any reaction?

Accepted Answer

A)  because it takes place in the mitochondrion 
B)  because it contains oxidation reactions 
C)  because it produces reduced electron carriers, which are reoxidized by transferring their electrons ultimately to oxygen 
D)  because NADH and FADH2 produce a lot of ATP when reoxidized 
E)  because it produces carbon dioxide

Question 18

Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which compound would you expect to decrease in concentration?

Accepted Answer

A)  citrate 
B)  fumarate 
C)  isocitrate 
D)  pyruvate 
E)  succinate

Question 19

Which process is NOT a metabolic fate for pyruvate in liver tissue?

Accepted Answer

A)  reduction to lactate 
B)  oxidative decarboxylation to acetyl-CoA 
C)  transamination to alanine 
D)  phosphorylation to phosphoenolpyruvate 
E)  carboxylation to oxaloacetate

Question 20

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

Accepted Answer

The answer of In which reaction of the citric acid...

Exam 16: The Citric Acid Cycle

Which statement is FALSE with respect to the pyruvate dehydrogenase complex?

Which statement about the oxidative decarboxylation of pyruvate in aerobic conditions in animal cells is CORRECT?

Which enzyme catalyzes a reversible reaction under normal cellular conditions?

Germinating plant seeds can convert stored fatty acids into oxaloacetate and a variety of carbohydrates. Animals cannot synthesize significant quantities of oxaloacetate or glucose from fatty acids. What accounts for this difference?

The oxidative decarboxylation of $\alpha$ -ketoglutarate proceeds by means of multistep reactions. Which cofactor is NOT required?

Which statement is FALSE regarding the glyoxylate cycle?

Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA?

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

When is the consumption of acetyl-CoA by the citric acid cycle is decreased?

Thyroxine is a competitive inhibitor of malate dehydrogenase. If thyroxine is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which compound would you expect to decrease in concentration FIRST?

Succinate can be synthesized from pyruvate via two distinct pathways that have no enzyme in common. What are the energy conditions of each pathway?

The citric acid cycle has an important anabolic function by:

Which enzyme in the citric acid cycle has a standard free energy that is large and positive?

Although ADP is not directly involved in the isocitrate dehydrogenase reaction, the activity of this enzyme is dependent on the concentration of ADP in the matrix. Briefly explain how.

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:

Why is the citric acid cycle considered to be part of aerobic metabolism, even though oxygen is not a substrate in any reaction?

Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which compound would you expect to decrease in concentration?

Which process is NOT a metabolic fate for pyruvate in liver tissue?

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

Exam 16: The Citric Acid Cycle

Which statement is FALSE with respect to the pyruvate dehydrogenase complex?

Which statement about the oxidative decarboxylation of pyruvate in aerobic conditions in animal cells is CORRECT?

Which enzyme catalyzes a reversible reaction under normal cellular conditions?

Germinating plant seeds can convert stored fatty acids into oxaloacetate and a variety of carbohydrates. Animals cannot synthesize significant quantities of oxaloacetate or glucose from fatty acids. What accounts for this difference?

The oxidative decarboxylation of α\alphaα -ketoglutarate proceeds by means of multistep reactions. Which cofactor is NOT required?

Which statement is FALSE regarding the glyoxylate cycle?

Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA?

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

When is the consumption of acetyl-CoA by the citric acid cycle is decreased?

Thyroxine is a competitive inhibitor of malate dehydrogenase. If thyroxine is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which compound would you expect to decrease in concentration FIRST?

Succinate can be synthesized from pyruvate via two distinct pathways that have no enzyme in common. What are the energy conditions of each pathway?

The citric acid cycle has an important anabolic function by:

Which enzyme in the citric acid cycle has a standard free energy that is large and positive?

Although ADP is not directly involved in the isocitrate dehydrogenase reaction, the activity of this enzyme is dependent on the concentration of ADP in the matrix. Briefly explain how.

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:

Why is the citric acid cycle considered to be part of aerobic metabolism, even though oxygen is not a substrate in any reaction?

Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which compound would you expect to decrease in concentration?

Which process is NOT a metabolic fate for pyruvate in liver tissue?

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

The oxidative decarboxylation of $\alpha$ -ketoglutarate proceeds by means of multistep reactions. Which cofactor is NOT required?

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