Deck 13: The Citric Acid Cycle

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.

Answer 1

oxaloacetate

Question 2

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

A) Malate dehydrogenase
B) Succinate dehydrogenase
C) α-ketoglutarate dehydrogenase
D) Isocitrate dehydrogenase
E) Succinyl -CoA synthetase

Answer 2

E

Question 3

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

A) Co-immunoprecipitation
B) Affinity chromatography
C) Chemical cross-linking
D) Surface plasmon resonance
E) The two-hybrid system

Answer 3

D
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.

Question 5

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

Question 6

Oxaloacetate is replenished via the ________ in plants and bacteria.

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.

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.

Question 9

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

A) Substrate availability
B) The ratio of [NAD+]/[NADH]
C) Allosteric inhibition of isocitrate dehydrogenase by ADP
D) Inhibition of α-ketoglutarate dehydrogenase by succinyl CoA
E) Ca2+ activation of isocitrate dehydrogenase

Question 10

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

A) The process is highly exergonic and essentially irreversible in vivo.
B) Each intermediate in the five step reaction is able to diffuse to the next active site in a sequential manner.
C) It takes place in the mitochondrion.
D) It is an oxidative decarboxylation.
E) The product is acetyl CoenzymeA.

Question 11

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

Question 12

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

Question 13

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

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.

Question 15

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

A) 6C02, 8 NADH/H+, 1FADH2 and 1 ATP.
B) 6C02, 8 NADH/H+, 1FADH2 and 2 ATP.
C) 6C02, 10 NADH/H+, 2FADH2 and 2 ATP.
D) 6C02, 10 NADH/H+, 2FADH2 and 4 ATP.
E) 6C02, 8 NADH/H+, 2FADH2 and 4 ATP.

Question 16

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

A) α-ketoglutarate dehydrogenase.
B) succinate dehydrogenase.
C) succinyl -CoA synthetase.
D) isocitrate dehydrogenase.
E) citrate synthase.

Question 17

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