Coenzyme
Definition and meaning of Coenzyme in chemistry.
Coenzyme is a small, organic, non-protein molecule that binds to an enzyme and is required for its catalytic activity, typically by acting as a carrier that accepts and transfers specific atoms, electrons, or functional groups during the reaction.
In more detail
Coenzymes are chemically altered during catalysis (for example, oxidized or reduced) and must be regenerated in a separate reaction before they can be reused, distinguishing them from the enzyme's protein structure, which is not consumed. Many coenzymes are derived from water-soluble vitamins, which is why vitamin deficiencies often impair specific metabolic pathways. A coenzyme that is loosely and reversibly bound is sometimes called a cosubstrate, while one that is tightly or covalently attached to the enzyme is called a prosthetic group.
Key facts
| Field | Biochemistry |
|---|---|
| Common examples | NAD+/NADH, FAD/FADH2, coenzyme A, coenzyme Q |
| Often derived from | Water-soluble vitamins (e.g., niacin, riboflavin, pantothenic acid) |
| Related term | Subtype of cofactor |
During glycolysis, the coenzyme NAD+ accepts a hydride ion and two electrons, becoming reduced to NADH; the NADH then carries those electrons to the electron transport chain, where it is reoxidized back to NAD+ for reuse.
Frequently asked questions
What is the difference between a coenzyme and a cofactor?
Cofactor is the broader category of any non-protein helper an enzyme needs, including inorganic metal ions (like Zn2+ or Mg2+); coenzyme specifically refers to the organic, often vitamin-derived cofactors.
Is a coenzyme permanently part of the enzyme?
Not usually. Most coenzymes bind, participate in the reaction, and are released in a changed form, then get regenerated separately; only when a coenzyme is tightly bound is it called a prosthetic group.