The Citric Cycle Flashcards
The citric acid cycle is the only metabolic pathway that can be used both as an anabolic and as
a catabolic pathway.
a. True
b. False
b. False
Which of the following statements concerning the citric acid cycle as the central metabolic
pathway is true?
a. It is involved in the metabolism of sugars and amino acids.
b. It is involved in the metabolism of amino acids and lipids.
c. It links anaerobic metabolism to aerobic metabolism.
d. Many of its intermediates are starting points for synthesis of a variety of compounds.
e. All of these are reasons why the citric acid cycle is considered to be the central
pathway.
e. All of these are reasons why the citric acid cycle is considered to be the central
pathway.
The citric acid cycle is amphibolic, meaning
a. it plays a role in both anabolism and catabolism.
b. it is essentially irreversible.
c. it can operate both in the presence and absence of
oxygen.
d. it can oxidize carbons and nitrogens equally well.
e. none of these
a. it plays a role in both anabolism and catabolism.
Roughly how many more ATP’s can be produced via the complete aerobic oxidation of glucose
compared to that produced by glycolysis alone?
a. twice as much
b. five times as much
c. fifteen times as much
d. thirty-two times as
much
e. none of these
c. fifteen times as much
Which of the following does not play a role in the overall aerobic metabolism of glucose?
a. citric acid cycle
b. electron transport
c. oxidative phosphorylation
d. urea cycle
e. all of these play a role in overall aerobic metabolism of
glucose
d. urea cycle
Which enzymes in the citric acid cycle catalyze oxidative decarboxylation reactions?
a. isocitrate dehydrogenase and the α-ketoglutarate dehydrogenase
complex
b. aconitase and succinate dehydrogenase
c. the α-ketoglutarate dehydrogenase complex and succinate thiokinase
d. fumarase and succinate dehydrogenase
a. isocitrate dehydrogenase and the α-ketoglutarate dehydrogenase
complex
In which cellular location do the majority of the reactions of the citric acid cycle take place?
a. the cytosol.
b. the mitochondrial matrix.
c. the endoplasmic
reticulum.
d. lysosomes.
e. none of these
b. the mitochondrial matrix.
The immediate electron acceptor for the majority of the oxidative reactions of the citric acid
cycle is
a. ATP.
b. NAD.
c. FAD.
d. coenzyme A.
e. none of these
b. NAD.
The citric acid cycle produces one high energy phosphate molecule per cycle directly in the
form of ____
a. ATP
b. GTP
c. CTP
d. AMP
e. none of these
b. GTP
The reaction of the citric acid cycle that does not take place in the mitochondrial matrix is the
one catalyzed by:
a. fumarase
b. citrate synthase
c. isocitrate dehydrogenase
d. succinate dehydrogenase
e. All of these reactions take place in the
matrix
d. succinate dehydrogenase
Which of the following is not a component of the pyruvate dehydrogenase complex?
a. pyruvate dehydrogenase
b. dihydrolipoyl transacetylase
c. dihydrolipoyl dehydrogenase
d. pyruvate dehydrogenase kinase
e. aconitase
e. aconitase
Thiamine pyrophosphate carries a ____ carbon unit.
a. 1
b. 2
c. 3
d. 4
b. 2
The acetyl group is carried on lipoic acid as
a. an alcohol.
b. a thioester.
c. a phosphoanhydride.
d. an amide.
b. a thioester.
Which of the following vitamins and enzyme cofactors are used by the pyruvate
dehydrogenase complex during oxidative decarboxylation?
a. Lipoic Acid.
b. Niacin.
c. Pantothenic
Acid.
d. Thiamine.
e. All of these
e. All of these
Which of the following is not a reaction occurring during oxidative decarboxylation of
pyruvate?
a. Removal of CO2.
b. Oxidation of an acetate group.
c. Addition of Coenzyme A to a 2-carbon fragment.
d. Reduction of NAD+
e. All of these reactions take place during oxidative
decarboxylation.
b. Oxidation of an acetate group.
The enzymes involved in the pyruvate dehydrogenase complex are
a. physically separated from each other
b. crosslinked to each other by lipoic acid linkers
c. covalently bonded to coenzyme A
d. associated with each other in an ordered and complex array
d. associated with each other in an ordered and complex array
Lipoic acid is a required vitamin in the human diet.
a. True
b. False
b. False
Each of the enzymes of the pyruvate dehydrogenase complex requires a different vitamin.
a. True
b. False
a. True
Which group of small molecules best fit the boxes associated with the reaction shown?
(see photo)
a. I
b. II
c. III
d. IV
b. II
The reactions in which succinate is converted to oxaloacetate are, in order
a. an oxidation, a dehydration, and an oxidation
b. three successive oxidation reactions
c. an oxidative decarboxylation, a dehydration, and a
condensation
d. a condensation, a dehydration, and an oxidative decarboxylation
a. an oxidation, a dehydration, and an oxidation
All but one of the enzymes of the citric acid cycle are found in this part of the mitochondrion:
a. The outer membrane.
b. The inner membrane.
c. The mitochondrial matrix.
d. The intermembrane space.
e. It is not known where these enzymes are located.
c. The mitochondrial matrix.
Which of the following enzymes contains a non-heme iron?
a. citrate synthase
b. succinyl-CoA
synthetase
c. succinate
dehydrogenase
d. fumarase
c. succinate
dehydrogenase
Which group of small molecules best fit the boxes associated with the reaction shown?
(see photo)
a. I
b. II
c. III
d. IV
d. IV
Which group of small molecules best fit the boxes associated with the reaction shown?
(see photo)
a. I
b. II
c. III
d. IV
a. I
Which of the following reactions involves substrate-level phosphorylation?
a. isocitrate → α-ketoglutarate
b. citrate → isocitrate
c. succinate → fumarate
d. succinyl-CoA → succinate
e. acetyl-CoA + oxaloacetate → citrate
d. succinyl-CoA → succinate
Which enzyme catalyzes the reaction shown?
(see photo)
a. isocitrate dehydrogenase
b. pyruvate dehydrogenase
c. fumarase
d. succinate
dehydrogenase
e. none of these
e. none of these
Which coenzyme listed below is not associated with the α-ketoglutarate dehydrogenase
complex?
a. thiamine
pyrophosphate
b. lipoic acid
c. biotin
d. NAD+
c. biotin
Which of the following enzymes is the only membrane-bound enzyme in the citric acid cycle?
a. Aconitase.
b. IsoCitrate Dehydrogenase.
c. Succinate Dehydrogenase.
d. Malate Dehydrogenase.
e. Alpha-Ketoglutarate Dehydrogenase
complex.
c. Succinate Dehydrogenase.
The iron ion, which is part of succinate dehydrogenase, is bonded to heme.
a. True
b. False
b. False
Which enzyme catalyzes the reaction shown?
(see photo)
a. isocitrate dehydrogenase
b. malate dehydrogenase
c. fumarase
d. succinate
dehydrogenase
e. none of these
d. succinate
dehydrogenase
Which enzyme catalyzes the reaction shown?
(see photo)
a. succinyl-CoA synthetase
b. succinate dehydrogenase
c. pyruvate dehydrogenase
d. α-ketoglutarate
dehydrogenase
a. succinyl-CoA synthetase
When acetyl-CoA reacts with oxaloacetate to form citrate
a. a new carbon-carbon bond is formed
b. an oxidative decarboxylation reaction takes place
c. a dehydration reaction takes place
d. a rearrangement takes place
e. none of these
a. a new carbon-carbon bond is formed
The order of compounds and intermediates found in the citric acid cycle is as follows:
a. IsoCitrate → Aconitate → α-Ketoglutarate → Fumarate → Malate → Oxaloacetate
b. Aconitate → IsoCitrate → Oxaloacetate → α-Ketoglutarate → Malate → Fumarate
c. Aconitate → IsoCitrate → α-Ketoglutarate → Fumarate → Malate → Oxaloacetate
d. Aconitate → IsoCitrate → α-Ketoglutarate → Malate → Fumarate → Oxaloacetate
e. IsoCitrate → Aconitate → α-Ketoglutarate → Malate → Oxaloacetate → Fumarate
c. Aconitate → IsoCitrate → α-Ketoglutarate → Fumarate → Malate → Oxaloacetate
Release of succinate from succinyl-CoA can be coupled to GTP synthesis because:
a. The amide bond between succinate and CoA has a large −ΔG of hydrolysis.
b. The thioester bond between succinate and CoA has a large −ΔG of hydrolysis.
c. The link between succinate and CoA involves an acid anhydride to
phosphate.
d. Coenzyme A is a “high energy” compound, just like GTP.
e. None of these explains why GTP can be formed during this reaction.
b. The thioester bond between succinate and CoA has a large −ΔG of hydrolysis.