Here's why:

* Structure: Coenzymes are typically derived from vitamins or other small organic molecules. They are much smaller than enzymes themselves.

* Function: Their role is to assist enzymes in their catalytic activity. They act as carriers of electrons, atoms, or functional groups.

* Example: NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) are common coenzymes that are essential for many metabolic reactions.

In contrast, enzymes are large protein molecules.