Multiple Choice Questions on Tricarboxylic Acid or TCA Cycle
1) The conversion of pyruvate to acetyl CoA is catalyzed by the enzyme pyruvate dehydrogenase. In this reaction
a) NADPH is oxidized to NADP
b) NADH is oxidized to NAD
c) NADP is reduced to NADPH
d) NAD is reduced to NADH
2) In the tricarboxylic acid cycle, the reaction for the conversion of pyruvate to acetyl CoA is known as
a) Oxidative decarboxylation
b) Oxidative phosphorylation
c) Reductive biosynthesis
d) Reductive decarboxylation
3) Which of the following is false regarding enzyme pyruvate dehydrogenase?
a) It is a multi-enzyme complex
b) It catalyzes the reversible reaction (conversion of pyruvate to acetyl CoA)
c) The pyruvate dehydrogenase complex is a mitochondrial enzyme
d) It requires thiamine, flavin, and nicotine vitamin co-enzymes
4) Pyruvate dehydrogenase is an important regulatory enzyme that senses the energy status of the cells. Which of the following is NOT the regulator of pyruvate dehydrogenase?
a) Calcium
b) Acetyl CoA
c) ATP
d) Citrate
5) Arsenic binds to the thiol group of lipoic acid and interferes with the activity of enzymes that require lipoic acid as a co-factor. Which of the following enzyme does not require lipoic acid for its activity and NOT directly inhibited by arsenic?
a) Pyruvate dehydrogenase
b) Isocitrate dehydrogenase
c) Malate dehydrogenase
d) Branched-chain amino acid dehydrogenase
6) Citrate synthase is the enzyme that catalyzes the condensation of acetyl CoA and oxaloacetate to citrate. Which of the following is an activator of this enzyme?
a) Succinyl CoA
b) NADH
c) Fatty Acyl CoA
d) ADP
7) Which of the following enzyme catalyzes substrate-level phosphorylation i.e conversion of GDP to GTP?
a) Malate dehydrogenase
b) Fumarase
c) Isocitrate dehydrogenase
d) Succinyl CoA thiokinase
8) In Krebs (TCA) cycle, when two carbon Acetyl CoA is oxidized to CO2, the total yield of ATP is
a) 8
b) 12
c) 14
d) 16
9) Which of the following is not the irreversible reaction of Kreb's cycle?
a) Isocitrate dehydrogenase
b) Alpha-ketoglutarate dehydrogenase
c) Citrate synthase
d) Malate dehydrogenase
10) Which of the following enzyme causes congenital lactic acidosis
a) Isocitrate dehydrogenase
b) Alpha-ketoglutarate dehydrogenase
c) Pyruvate dehydrogenase
d) Malate dehydrogenase
11) Which of the following enzyme of the TCA cycle catalyzes co-reduction of FAD+ to FADH2?
a) Isocitrate dehydrogenase
b) Alpha-ketoglutarate dehydrogenase
c) Succinate Dehydrogenase
d) Malate dehydrogenase
b) Alpha-ketoglutarate dehydrogenase
c) Succinate Dehydrogenase
d) Malate dehydrogenase
12) TCA cycle is also known as the amphibolic pathway (function both in oxidative and synthetic processes). Which of the following is a correct statement regarding
a) Alpha-ketoglutarate plays a critical role in amino acid metabolism
b) Oxaloacetate is an intermediate for gluconeogenesis and fatty acid synthesis
c) Succinyl CoA is involved in ketone body metabolism
d) All of the above
13) Which of the following metabolic intermediate activates the TCA cycle?
a) High NADH/NAD ratio
b) High ADP/ATP ratio
c) High Oxaloacetate
d) None of the above
Multiple Choice Answers
1- d) NAD is reduced to NADH
2- a) Oxidative decarboxylation
3-b) It catalyzes the reversible reaction (conversion of pyruvate to acetyl CoA)
4-d) Citrate
5-c) Malate dehydrogenase
6-d) ADP
7-d) Succinyl CoA thiokinase
8-b) 12
9-d) Malate dehydrogenase
10-c) Pyruvate dehydrogenase
1- d) NAD is reduced to NADH
2- a) Oxidative decarboxylation
3-b) It catalyzes the reversible reaction (conversion of pyruvate to acetyl CoA)
4-d) Citrate
5-c) Malate dehydrogenase
6-d) ADP
7-d) Succinyl CoA thiokinase
8-b) 12
9-d) Malate dehydrogenase
10-c) Pyruvate dehydrogenase
11-c) Succinate Dehydrogenase
12-d) All of the above
13-c) High Oxaloacetate
