Question 1

The malate dehydrogenase reaction has a strongly positive standard free energy change but it proceeds in the direction of oxaloacetate because the concentration of ________ is maintained at exceedingly low levels.

Accepted Answer

oxaloacetate

Question 2

Which of the following enzymes catalyzes a reaction of the citric acid cycle that does NOT produce reduced electron carriers?

Accepted Answer

Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate, which does not involve the production of reduced electron carriers. The other enzymes listed in the answer choices, Malate dehydrogenase, Succinate dehydrogenase, α-ketoglutarate dehydrogenase, and Isocitrate dehydrogenase all catalyze reactions that produce reduced electron carriers.

Question 3

Which of the following techniques can be used to quantify protein-protein interactions?

Accepted Answer

Global LO: G9

Question 4

Arsenic poisoning acts by inhibiting the citric acid cycle at the point of both pyruvate dehydrogenase and α-ketoglutarate dehydrogenase because it makes a stable adduct with the ________ groups of the dihydrolipoamide intermediate.

Accepted Answer

The answer of Arsenic poisoning acts by inhibiting the citric...

Question 5

All of the enzymes of the citric acid cycle are located in the mitochondrion.

Accepted Answer

This statement is true. All of the enzymes of the citric acid cycle are located in the mitochondrial matrix, which is the space enclosed by the inner membrane of the mitochondrion. This location ensures that the citric acid cycle intermediates can easily shuttle between enzymes and that the energy released from the cycle can be efficiently used for ATP production by the respiratory chain located in the inner mitochondrial membrane.

Question 6

Oxaloacetate is replenished via the ________ in plants and bacteria.

Accepted Answer

The answer of Oxaloacetate is replenished via the ________ in...

Question 7

The citric acid cycle can be considered both a ________ and anabolic pathway as it is used to oxidise acetyl CoA to carbon dioxide as well as to provide precursors for other ________ pathways.

Accepted Answer

The answer of The citric acid cycle can be considered...

Question 8

The glyoxylate cycle in plants and bacteria can be used for net carbohydrate synthesis from fat because isocitrate lyase yields glyoxylate and ________ without the loss of two carbons as occurs in the citric acid cycle.

Accepted Answer

The answer of The glyoxylate cycle in plants and bacteria...

Question 9

Which of the following does NOT regulate flux through the citric acid cycle?

Accepted Answer

The answer of Which of the following does NOT regulate...

Question 10

Which of the following does NOT apply to the reaction catalyzed by the pyruvate dehydrogenase complex?

Accepted Answer

The reaction catalyzed by the pyruvate dehydrogenase complex is not a sequential reaction in which intermediates diffuse to the next active site in order. Instead, the intermediates are bound to specific active sites within the complex and undergo a series of coordinated reactions.

Question 11

NAD+, coenzyme A, thiamine pyrophosphate, lipoic acid and FAD are all cofactors used in the reaction catalyzed by pyruvate dehydrogenase.

Accepted Answer

These cofactors are all necessary for the conversion of pyruvate to acetyl-CoA by pyruvate dehydrogenase. NAD+ and FAD are involved in oxidation-reduction reactions, coenzyme A is necessary for the transfer of the acetyl group, thiamine pyrophosphate serves as a cofactor for the enzyme, and lipoic acid is involved in the transfer of acetyl groups between different enzymes in the reaction.

Question 12

Acetyl CoA is a feed forward activator of the enzyme ________ ensuring sufficient oxaloacetate for the citric acid cycle to continue.

Accepted Answer

The answer of Acetyl CoA is a feed forward activator...

Question 13

The citric acid cycle is classed as a reductive pathway as it produces reduced electron carriers.

Accepted Answer

The citric acid cycle is actually classified as an oxidative pathway because it involves the oxidation of acetyl-CoA to produce electron carriers such as NADH and FADH2.

Question 14

The two carbon atoms that are lost as CO2 in the third and fourth steps of the citric acid cycle are the same as the two carbon atoms of acetyl CoA because of the stereochemistry of the isocitrate dehydrogenase reaction.

Accepted Answer

The two carbon atoms lost as CO2 in the citric acid cycle are not the same two carbon atoms that enter the cycle as part of acetyl CoA. The cycle involves a series of transformations where the acetyl group (a 2-carbon molecule) from acetyl CoA combines with oxaloacetate (a 4-carbon molecule) to form citrate (a 6-carbon molecule). The carbon atoms lost as CO2 come from the original oxaloacetate and other intermediates, not directly from the acetyl group added.

Question 15

Taking one mole of glucose through glycolysis and the citric acid cycle generates:

Accepted Answer

One mole of glucose generates 2 pyruvate molecules which are converted to Acetyl-CoA in the presence of oxygen. Two molecules of Acetyl-CoA enter the citric acid cycle which generates 6 CO2, 8 NADH/H+, 2 FADH2, and 2 ATP. The NADH and FADH2 molecules generated from the citric acid cycle will be used in oxidative phosphorylation to generate ATP. The net ATP generated through glycolysis and the citric acid cycle only is 2. Therefore, the correct answer is D, which is the only option that includes 6 CO2, 10 NADH/H+, 2 FADH2, and 4 ATP.

Question 16

One substrate level phosphorylation occurs in the citric acid cycle in the reaction catalyzed by:

Accepted Answer

Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate and uses the energy released to phosphorylate ADP to ATP, representing a substrate-level phosphorylation in the citric acid cycle. The other enzymes listed do not catalyze reactions that involve substrate-level phosphorylation.

Question 17

Transamination reactions can be used to provide intermediates for the citric acid cycle.

Accepted Answer

Transamination reactions involve transferring the amino group from an amino acid to a keto acid to form a different amino acid and a new keto acid. The new keto acid produced can then enter the citric acid cycle as an intermediate. Thus, transamination reactions can provide intermediates for the citric acid cycle.

Quiz 13: The Citric Acid Cycle