The inactive form of an enzyme is known as a/an:

• A. Inactive enzyme
• B. Coenzyme
• C. Zymogen
• D. Proenzyme

Answer: (C)

An enzyme in its inactive form is called a zymogen. A zymogen is an enzyme precursor that contains an inhibitory segment blocking the active site and must be proteolytically cleaved to become active. This regulated activation prevents digestive enzymes from harming tissues and allows activation at the correct site, such as pepsinogen turning into pepsin in the stomach or trypsinogen into trypsin in the small intestine. Proenzyme is another term used for the same idea, but zymogen is the classic, widely used term for digestive enzyme precursors. Coenzyme is not related to an inactive enzyme; it’s a nonprotein molecule that assists enzyme activity.