What is a zymogen?

A zymogen is indeed an inactive enzyme precursor that requires a biochemical change for it to become an active enzyme. This transformation usually involves the cleavage of specific peptide bonds within the zymogen molecule, which results in a conformational change that activates the enzyme.

For example, many digestive enzymes, such as pepsinogen, are secreted as zymogens to prevent them from digesting proteins in the cells that produce them. Once they reach the appropriate site in the digestive tract, they are activated into their enzymatically active forms. This controlled activation mechanism is crucial for maintaining cellular integrity and ensuring that enzymes function only when and where needed.

In this context, other options do not accurately describe a zymogen. Active enzymes that function immediately are not zymogens, while coenzymes are auxiliary molecules that assist enzymes rather than being precursors to them. Lastly, a degraded form of an enzyme refers to a breakdown product rather than an inactive precursor subjected to activation.