DAT Molecules and Biology Practice Test 2026 – Complete Exam Prep

The key idea is that enzymes can be active only when they have their nonprotein helpers, called cofactors. The protein portion by itself, without those cofactors, is called an apoenzyme. That means it’s inactive until a cofactor binds. Once the cofactor is bound, the whole complex becomes a holoenzyme and is ready to catalyze reactions.

Cofactors are the nonprotein parts needed for activity; a prosthetic group is a cofactor that is tightly bound and essentially part of the enzyme's structure, remaining attached under most conditions. So, an enzyme without its cofactors is specifically an apoenzyme, the inactive form.