Citric Acid Cycle

citric acid cycle

Q. 1

All of the following vitamins are required in citric acid cycle, EXCEPT:

 A

Riboflavin

 B

Niacin

 C

Thiamin

 D

Ascorbic acid

Q. 1

All of the following vitamins are required in citric acid cycle, EXCEPT:

 A

Riboflavin

 B

Niacin

 C

Thiamin

 D

Ascorbic acid

Ans. D

Explanation:

Four of the B vitamins are essential in the citric acid cycle and hence energy-yielding metabolism: (1) riboflavin, in the form of flavin adenine dinucleotide (FAD), a cofactor for succinate dehydrogenase; (2) niacin, in the form of nicotinamide adenine dinucleotide (NAD), the electron acceptor for isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase; (3) thiamin (vitamin B1), as thiamin diphosphate, the coenzyme for decarboxylation in the α-ketoglutarate dehydrogenase reaction; and (4) pantothenic acid, as part of coenzyme A, the cofactor attached to “active” carboxylic acid residues such as acetyl-CoA and succinyl-CoA
 
Ref: Harper 28th edition, chapter 17

Q. 2

The citric acid cycle is inhibited by which of the following?

 A

Fluoroacetate

 B

Fluorouracil

 C

Arsenic

 D

Aerobic conditions

Q. 2

The citric acid cycle is inhibited by which of the following?

 A

Fluoroacetate

 B

Fluorouracil

 C

Arsenic

 D

Aerobic conditions

Ans. A

Explanation:

Fluoroacetate can be converted to fluorocitrate, which is an inhibitor of aconitase. Arsenic is not a direct inhibitor, but arsenite is an inhibitor of lipoic acid–containing enzymes such as α-ketoglutarate dehydrogenase. Malonate, not malic acid, is an inhibitor of succinate dehydrogenase. The citric acid cycle requires oxygen and would be inhibited by anaerobic, not aerobic, conditions. Fluorouracil is a suicide inhibitor of thymidylate synthase and blocks deoxythymidylate synthesis. 

Ref: Bender D.A., Mayes P.A. (2011). Chapter 17. The Citric Acid Cycle: The Catabolism of Acetyl-CoA. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

Q. 3

In vivo control of citric acid cycle is effected by:

 A

Acetyl CoA

 B

Coenzyme A

 C

ATP

 D

Citrate

Q. 3

In vivo control of citric acid cycle is effected by:

 A

Acetyl CoA

 B

Coenzyme A

 C

ATP

 D

Citrate

Ans. C

Explanation:

C i.e. ATP, E i.e. NADH

Quiz In Between


Q. 4

Which end product of citric acid cycle is used in detoxification of ammonia in brain?

 A

Oxaloacetate

 B

Alphaketoglutarate

 C

Succinate

 D

Citrate

Q. 4

Which end product of citric acid cycle is used in detoxification of ammonia in brain?

 A

Oxaloacetate

 B

Alphaketoglutarate

 C

Succinate

 D

Citrate

Ans. B

Explanation:

Q. 5

All are components of Citric acid cycle EXCEPT:

 A

Fumarase

 B

Malonate

 C

Succinate dehydrogenase

 D

Alpha-ketoglutarate dehydrogenase

Q. 5

All are components of Citric acid cycle EXCEPT:

 A

Fumarase

 B

Malonate

 C

Succinate dehydrogenase

 D

Alpha-ketoglutarate dehydrogenase

Ans. B

Explanation:

 

Malonate competitively inhibits succinate dehydrogenase, which converts succinate to fumarate


Q. 6

Which of the following glucogenic amino acid enters the citric acid cycle at succinyl CoA

 A

Phenylalanine

 B

Tyrosine

 C

Isoleucine

 D

Tryptophan

Q. 6

Which of the following glucogenic amino acid enters the citric acid cycle at succinyl CoA

 A

Phenylalanine

 B

Tyrosine

 C

Isoleucine

 D

Tryptophan

Ans. C

Explanation:

Ans. is ‘c’ i.e., isoleucine

Quiz In Between


Q. 7

Not an intermediate product of citric acid cycle is:

 A

Acyl Co-A

 B

Succinyl Co-A

 C

Citrate

 D

a-ketoglutarate

Q. 7

Not an intermediate product of citric acid cycle is:

 A

Acyl Co-A

 B

Succinyl Co-A

 C

Citrate

 D

a-ketoglutarate

Ans. A

Explanation:

Ans. a. Acetyl Co-A


Q. 8

Substrate level phosphorylation is seen in reaction catalyzed by which enzyme of citric acid cycle‑

 A

Pyruvate kinase

 B

Succinate thiokinase

 C

Phosphoglycerate kinase

 D

All of the above

Q. 8

Substrate level phosphorylation is seen in reaction catalyzed by which enzyme of citric acid cycle‑

 A

Pyruvate kinase

 B

Succinate thiokinase

 C

Phosphoglycerate kinase

 D

All of the above

Ans. B

Explanation:

Ans. is ‘b’ i.e., Succinate thiokinase 

Quiz In Between



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