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Biomolecules

Coenzymes and cofactors Practice Questions

19 free Coenzymes and cofactors practice questions for the NCERT Biology. 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 19 Medium

Cofactors are best defined as:

  1. A Proteins that catalyze reactions
  2. B Energy molecules
  3. C Structural lipids
  4. D Non-protein helpers of enzymes

Correct answer: Non-protein helpers of enzymes

Cofactors are non-protein substances that assist enzymes in catalysis. Without them, many enzymes remain inactive.

Question 2 of 19 Medium

Which of the following is an organic cofactor?

  1. A Metal ions
  2. B Salt
  3. C Water
  4. D Coenzyme

Correct answer: Coenzyme

Coenzymes are organic molecules that act as cofactors. They often participate in enzyme-catalyzed reactions.

Question 3 of 19 Medium

Which of the following is an example of a coenzyme?

  1. A Zn2+
  2. B Mg2+
  3. C NAD+
  4. D Fe2+

Correct answer: NAD+

NAD+ is an organic coenzyme involved in redox reactions. It carries electrons during metabolism.

Question 4 of 19 Medium

Which of the following is an inorganic cofactor?

  1. A FAD
  2. B Coenzyme A
  3. C Mg2+
  4. D NADH

Correct answer: Mg2+

Inorganic cofactors are usually metal ions like Mg2+. They assist enzyme activity by stabilizing structures.

Question 5 of 19 Medium

Coenzymes are typically derived from:

  1. A Proteins
  2. B Lipids
  3. C Vitamins
  4. D Carbohydrates

Correct answer: Vitamins

Many coenzymes are derived from vitamins. For example, NAD+ is derived from niacin.

Question 6 of 19 Medium

Which function is performed by coenzymes?

  1. A Support of cellular structures
  2. B Energy storage
  3. C Transfer of chemical groups
  4. D DNA replication

Correct answer: Transfer of chemical groups

Coenzymes help transfer chemical groups or electrons. This is essential for enzyme-mediated reactions.

Question 7 of 19 Medium

Which term refers to the inactive enzyme without its cofactor?

  1. A Apoenzyme
  2. B Holoenzyme
  3. C Coenzyme
  4. D Substrate

Correct answer: Apoenzyme

An apoenzyme is the protein part of an enzyme without its cofactor. It is inactive alone.

Question 8 of 19 Medium

What is a holoenzyme?

  1. A Inactive enzyme
  2. B Enzyme without its cofactor
  3. C Substrate complex
  4. D Active enzyme with cofactor

Correct answer: Active enzyme with cofactor

A holoenzyme is the complete, active enzyme. It consists of apoenzyme plus cofactor.

Question 9 of 19 Medium

Which of the following is a prosthetic group?

  1. A FAD
  2. B NAD+
  3. C Mg2+
  4. D ATP

Correct answer: FAD

FAD can act as a prosthetic group when tightly bound. It participates in oxidation-reduction reactions.

Question 10 of 19 Medium

Which coenzyme is involved in electron transfer?

  1. A NAD+
  2. B CoA
  3. C Biotin
  4. D Thiamine

Correct answer: NAD+

NAD+ accepts and donates electrons during metabolic reactions. It is essential for cellular respiration.

Question 11 of 19 Medium

Which coenzyme is involved in acyl group transfer?

  1. A NAD+
  2. B FAD
  3. C Biotin
  4. D CoA

Correct answer: CoA

Coenzyme A carries acyl groups. It plays a key role in fatty acid metabolism.

Question 12 of 19 Medium

Which of the following is a characteristic of cofactors?

  1. A They are protein molecules
  2. B They are consumed in reactions
  3. C They store genetic information
  4. D They assist enzyme function

Correct answer: They assist enzyme function

Cofactors assist enzymes in catalysis. They are not enzymes themselves but are essential for activity.

Question 13 of 19 Medium

Which metal ion acts as a cofactor for many enzymes?

  1. A Na+
  2. B Cl-
  3. C H+
  4. D Mg2+

Correct answer: Mg2+

Mg2+ is a common cofactor. It stabilizes enzyme-substrate complexes and participates in catalysis.

Question 14 of 19 Medium

Which of the following distinguishes coenzymes from prosthetic groups?

  1. A Coenzymes are loosely bound
  2. B Coenzymes are inorganic
  3. C Prosthetic groups are unbound
  4. D Coenzymes are proteins

Correct answer: Coenzymes are loosely bound

Coenzymes are loosely bound and can dissociate from enzymes. Prosthetic groups remain tightly bound.

Question 15 of 19 Medium

Which cofactor is required for DNA polymerase activity?

  1. A Mg2+
  2. B Fe2+
  3. C Na+
  4. D K+

Correct answer: Mg2+

Mg2+ is essential for DNA polymerase function. It helps in nucleotide addition during DNA synthesis.

Question 16 of 19 Medium

Which vitamin-derived coenzyme is involved in carboxylation reactions?

  1. A Biotin
  2. B NAD+
  3. C FAD
  4. D Coenzyme A

Correct answer: Biotin

Biotin acts as a coenzyme in carboxylation reactions. It helps add CO2 groups to substrates.

Question 17 of 19 Medium

Which coenzyme participates in redox reactions along with FAD?

  1. A ATP
  2. B NAD+
  3. C Biotin
  4. D Coenzyme A

Correct answer: NAD+

NAD+ works alongside FAD in redox reactions. Both transfer electrons during metabolism.

Question 18 of 19 Medium

Which of the following is true about cofactors?

  1. A They are used up permanently in each reaction
  2. B They are part of enzyme structure or function
  3. C They are always short strands of DNA
  4. D They are simple standalone energy molecules

Correct answer: They are part of enzyme structure or function

Cofactors may be part of enzyme structure or assist in function. They are essential for enzyme activity.

Question 19 of 19 Medium

Which term describes enzymes that require cofactors to function?

  1. A Inactive enzymes
  2. B Complete enzymes
  3. C Holoenzymes
  4. D Catalysts

Correct answer: Holoenzymes

Holoenzymes are enzymes with their required cofactors. They are fully active and functional.

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