An enzyme is a protein that acts as a catalyst to increase the biochemical reaction rate without altering itself in the process, while a coenzyme is an organic non-protein molecule that is required by an enzyme to perform its catalytic activity. Therefore, these two types of molecules differ in quite a few aspects:

• Size: Enzymes are large molecules, while coenzymes are usually small molecules.
• Nature: Enzymes are mainly globular proteins, whereas coenzymes are non-protein molecules.
• Function: Enzymes are biological catalysts; while coenzymes are helper molecules to the enzymes, which is necessary for the enzyme to execute its catalytic activity.
• Change of structure: Enzymes’ structure remains unaltered throughout the reaction, whereas coenzymes are chemically changed after the enzymatic reaction.