What is cofactor?
A A chemical that is necessary for enzymes to function
B. A chemical that inhibits enzymes.
C. A secondary substrate
D. An inorganic molecule that activates an zyme.
The correct answer and explanation is:
Correct Answer: A. A chemical that is necessary for enzymes to function
Explanation (300 words):
A cofactor is a non-protein chemical compound that is required for the biological activity of some enzymes. Many enzymes cannot function properly without the assistance of cofactors, as these molecules help the enzyme achieve its correct shape or participate directly in the enzyme’s chemical reaction. Thus, Option A is the most accurate definition: a chemical that is necessary for enzymes to function.
Cofactors can be either inorganic or organic:
- Inorganic cofactors: These include metal ions such as magnesium (Mg²⁺), iron (Fe²⁺), zinc (Zn²⁺), and copper (Cu²⁺). These metal ions may help stabilize the enzyme’s structure or participate in the enzyme’s catalytic action.
- Organic cofactors, also known as coenzymes, are carbon-based molecules like vitamins or compounds derived from vitamins (e.g., NAD⁺, FAD, coenzyme A). Coenzymes often act as carriers of electrons or chemical groups during the enzymatic reaction.
Cofactors work by:
- Assisting in the binding of substrates to the enzyme.
- Participating in chemical transformations.
- Helping the enzyme maintain the correct three-dimensional structure for activity.
Without the required cofactor, the enzyme is often inactive. The enzyme plus its cofactor is referred to as a holoenzyme, whereas the protein portion alone (without the cofactor) is called an apoenzyme.
Why the other options are incorrect:
- B: This describes an inhibitor, not a cofactor.
- C: A cofactor is not a substrate (primary or secondary), but a helper molecule.
- D: This is partially correct, but too narrow—cofactors include both organic and inorganic molecules, not just inorganic ones.
Therefore, Option A best represents the complete and accurate definition of a cofactor.