The Citric Acid 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
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
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
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
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
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
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 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
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
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
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
Thiamine pyrophosphate carries a ____ carbon unit.
a. 1
b. 2
c. 3
d. 4
b
The acetyl group is carried on lipoic acid as
a. an alcohol.
b. a thioester.
c. a phosphoanhydride.
d. an amide.
b
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
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
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
Lipoic acid is a required vitamin in the human diet.
a. True
b. False
b
Each of the enzymes of the pyruvate dehydrogenase complex requires a different vitamin.
a. True
b. False
a
- Which group of small molecules best fit the boxes associated with the reaction shown?
(picture)
a b I. ADP + 2 Pi ATP II. NAD+ NADH III. NADP+ NADPH IV. FAD FADH2
b
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
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
Which of the following enzymes contains a non-heme iron?
a. citrate synthase
b. succinyl-CoA synthetase
c. succinate dehydrogenase
d. fumarase
c
- Which group of small molecules best fit the boxes associated with the reaction shown?
(picture)
a b I. ADP + 2 Pi ATP II. NAD+ NADH III. ATP ADP + 2 Pi IV. FAD FADH2
d
- Which group of small molecules best fit the boxes associated with the reaction shown?
(picture)
a b I. NAD+ NADH II. NADP+ NADPH III. ADP + Pi ATP IV. FAD FADH2
a
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
- Which enzyme catalyzes the reaction shown?
(picture)
a. isocitrate dehydrogenase
b. pyruvate dehydrogenase
c. fumarase
d. succinate dehydrogenase
e. none of these
e
Which coenzyme listed below is not associated with the α-ketoglutarate dehydrogenase complex?
a. thiamine pyrophosphate
b. lipoic acid
c. biotin
d. NAD+
c
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
The iron ion, which is part of succinate dehydrogenase, is bonded to heme.
a. True
b. False
b
- Which enzyme catalyzes the reaction shown?
(picture)
a. isocitrate dehydrogenase
b. malate dehydrogenase
c. fumarase
d. succinate dehydrogenase
e. none of these
d
- Which enzyme catalyzes the reaction shown?
(picture)
a. succinyl-CoA synthetase
b. succinate dehydrogenase
c. pyruvate dehydrogenase
d. α-ketoglutarate dehydrogenase
a
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
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
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