enzyme

An enzyme is a tiny molecular helper inside living things — almost always a protein — that makes a specific chemical reaction happen millions of times faster, then walks away unchanged to do it again. Think of it as a matchmaker that brings the right molecules together so a reaction that would normally crawl can finish in a blink.

It works by lowering the "energy barrier" that a reaction has to climb. Each enzyme is shaped to fit one particular job, like a lock that only certain keys fit, so cells use thousands of different enzymes to run thousands of different reactions.

You meet enzymes every day: the ones in your saliva and gut break food into pieces small enough to absorb. Because an enzyme isn't consumed, a single one can do its job over and over, which is why a little goes a long way.