Without enzymes, these reactions would occur too slowly or not at all, and no life would be possible. Enzymes All living cells make enzymes, but enzymes are not alive.
Enzyme molecules function by altering other molecules.
Enzymes combine with the altered molecules to form a complex molecular structure in which chemical reactions take place. The enzyme, which remains unchanged, then separates from the product of the reaction. A single enzyme molecule can perform its entire function a million times a minute. The chemical reactions occur thousands or even millions of times faster with enzymes than without them. Most enzymes are proteins.