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Biochemistry

Vitamins and Coenzymes Practice Questions

20 free Vitamins and Coenzymes practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 20 Medium

Which vitamin functions primarily as a coenzyme in oxidative decarboxylation reactions?

  1. A Vitamin B1 (Thiamine)
  2. B Vitamin B2 (Riboflavin)
  3. C Vitamin B6 (Pyridoxine)
  4. D Vitamin C (Ascorbic acid)

Correct answer: Vitamin B1 (Thiamine)

Vitamin B1 is converted to thiamine pyrophosphate, a coenzyme required for oxidative decarboxylation of alpha-keto acids. It is essential for carbohydrate metabolism.

Question 2 of 20 Medium

FAD and FMN are coenzyme forms derived from which vitamin?

  1. A Niacin
  2. B Riboflavin
  3. C Pantothenic acid
  4. D Biotin

Correct answer: Riboflavin

Riboflavin is the precursor of FAD and FMN. These coenzymes participate in redox reactions in metabolic pathways.

Question 3 of 20 Medium

NAD+ and NADP+ are coenzymes derived from:

  1. A Vitamin B1
  2. B Vitamin B2
  3. C Vitamin B3
  4. D Vitamin B12

Correct answer: Vitamin B3

Vitamin B3, also known as niacin, is the precursor of NAD+ and NADP+. These coenzymes are essential for oxidation-reduction reactions.

Question 4 of 20 Medium

Which vitamin is essential for the synthesis of coenzyme A?

  1. A Biotin (vitamin B7)
  2. B Pantothenic acid
  3. C Folic acid
  4. D Pyridoxine

Correct answer: Pantothenic acid

Pantothenic acid is a component of coenzyme A. Coenzyme A plays a central role in acyl group transfer reactions.

Question 5 of 20 Medium

Which vitamin acts as a coenzyme in transamination reactions?

  1. A Vitamin B6
  2. B Vitamin B12
  3. C Vitamin C
  4. D Vitamin A

Correct answer: Vitamin B6

Vitamin B6 is converted to pyridoxal phosphate, which is required for transamination and amino acid metabolism. It facilitates transfer of amino groups.

Question 6 of 20 Medium

Biotin primarily functions as a coenzyme in:

  1. A Decarboxylation reactions
  2. B Carboxylation reactions
  3. C Oxidation reactions
  4. D Deamination reactions

Correct answer: Carboxylation reactions

Biotin acts as a coenzyme in carboxylation reactions. It carries activated carbon dioxide in metabolic pathways.

Question 7 of 20 Medium

Which vitamin is essential for one-carbon metabolism and nucleotide synthesis?

  1. A Vitamin B6 (pyridoxine)
  2. B Vitamin B9
  3. C Vitamin B2
  4. D Vitamin B1

Correct answer: Vitamin B9

Vitamin B9, or folic acid, participates in one-carbon transfer reactions. It is vital for DNA synthesis and cell division.

Question 8 of 20 Medium

Methylcobalamin is an active coenzyme form of which vitamin?

  1. A Vitamin B6 (pyridoxine)
  2. B Vitamin B9
  3. C Vitamin B12
  4. D Vitamin C

Correct answer: Vitamin B12

Vitamin B12 forms methylcobalamin and adenosylcobalamin. These coenzymes are involved in methyl transfer and rearrangement reactions.

Question 9 of 20 Medium

Which vitamin acts as an antioxidant and participates in collagen synthesis?

  1. A Vitamin A (retinol)
  2. B Vitamin D
  3. C Vitamin E
  4. D Vitamin C

Correct answer: Vitamin C

Vitamin C acts as a reducing agent and antioxidant. It is also essential for hydroxylation of proline and lysine in collagen synthesis.

Question 10 of 20 Medium

Vitamin K is primarily required for:

  1. A Bone mineralization
  2. B Blood clotting
  3. C Vision
  4. D Energy metabolism

Correct answer: Blood clotting

Vitamin K is required for synthesis of clotting factors. It enables gamma-carboxylation of specific proteins involved in coagulation.

Question 11 of 20 Medium

Which fat-soluble vitamin functions as an antioxidant protecting cell membranes?

  1. A Vitamin A (retinol)
  2. B Vitamin D
  3. C Vitamin E
  4. D Vitamin K

Correct answer: Vitamin E

Vitamin E protects polyunsaturated fatty acids in membranes from oxidative damage. It acts as a lipid-soluble antioxidant.

Question 12 of 20 Medium

Which vitamin deficiency impairs formation of visual pigments?

  1. A Vitamin A
  2. B Vitamin D (calciferol)
  3. C Vitamin E
  4. D Vitamin K

Correct answer: Vitamin A

Vitamin A is required for synthesis of retinal, a component of visual pigments. Deficiency leads to impaired vision, especially in low light.

Question 13 of 20 Medium

Which coenzyme is involved in acyl group transfer reactions?

  1. A NAD+
  2. B FAD (flavin adenine)
  3. C Coenzyme A
  4. D Biotin

Correct answer: Coenzyme A

Coenzyme A transfers acyl groups via thioester bonds. It is central to fatty acid metabolism and the citric acid cycle.

Question 14 of 20 Medium

Which vitamin is necessary for calcium absorption and bone health?

  1. A Vitamin A (retinol)
  2. B Vitamin C
  3. C Vitamin D
  4. D Vitamin E

Correct answer: Vitamin D

Vitamin D regulates calcium and phosphate metabolism. It promotes absorption of calcium from the intestine.

Question 15 of 20 Medium

Which vitamin-derived coenzyme participates in redox reactions of the electron transport chain?

  1. A Thiamine pyrophosphate
  2. B FAD
  3. C Pyridoxal phosphate
  4. D Biotin

Correct answer: FAD

FAD is a flavin coenzyme involved in oxidation-reduction reactions. It functions as an electron carrier in the electron transport chain.

Question 16 of 20 Medium

Which vitamin acts as a coenzyme in the conversion of homocysteine to methionine?

  1. A Vitamin B6 (pyridoxine)
  2. B Vitamin B9
  3. C Vitamin B12
  4. D Vitamin C

Correct answer: Vitamin B12

Vitamin B12 is required for methyl transfer from folate to homocysteine. This reaction forms methionine and prevents homocysteine accumulation.

Question 17 of 20 Medium

Which vitamin deficiency affects energy metabolism by impairing glycolysis and the citric acid cycle?

  1. A Vitamin B1
  2. B Vitamin B7 (biotin)
  3. C Vitamin A
  4. D Vitamin K

Correct answer: Vitamin B1

Vitamin B1 deficiency disrupts carbohydrate metabolism. Thiamine-dependent enzymes are essential for glycolysis-linked pathways.

Question 18 of 20 Medium

Which vitamin acts as a precursor of a hormone-like regulator rather than a classical coenzyme?

  1. A Vitamin B2
  2. B Vitamin D
  3. C Vitamin B6
  4. D Vitamin C

Correct answer: Vitamin D

Vitamin D functions as a hormone-like regulator of gene expression. It is not a classical coenzyme in metabolic reactions.

Question 19 of 20 Medium

Which vitamin-derived coenzyme participates in amino acid decarboxylation?

  1. A Thiamine pyrophosphate
  2. B Pyridoxal phosphate
  3. C FAD
  4. D NAD+

Correct answer: Pyridoxal phosphate

Pyridoxal phosphate, derived from vitamin B6, is required for amino acid decarboxylation. It stabilizes reaction intermediates during amino acid metabolism.

Question 20 of 20 Medium

Which group of vitamins primarily function as coenzymes in metabolism?

  1. A Fat-soluble vitamins
  2. B Steroid vitamins
  3. C B-complex vitamins
  4. D Vitamin A group

Correct answer: B-complex vitamins

Most B-complex vitamins serve as coenzymes or coenzyme precursors. They are essential for energy metabolism and biosynthetic reactions.

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