An enzyme is a special protein that speeds up chemical reactions in living things. Think of enzymes as tiny molecular machines that make things happen faster inside cells. Without enzymes, the chemical reactions that keep you alive would take years instead of seconds.

Your body contains thousands of different enzymes, each designed to do a specific job. Some enzymes in your saliva start breaking down food the moment it enters your mouth. Enzymes in your stomach help digest proteins. Other enzymes help your cells turn food into energy, build new proteins, or copy DNA when cells divide.

What makes enzymes remarkable is their precision. Each enzyme has a uniquely shaped pocket that fits only certain molecules, like a lock that accepts only one key. When the right molecule slides into this pocket, the enzyme either breaks it apart or joins it with something else, then releases the result and moves on to the next molecule. A single enzyme can repeat this process thousands of times per second.

Scientists use enzymes in many products. Laundry detergents contain enzymes that break down stains. Cheese makers use enzymes to curdle milk. Even some contact lens cleaners use enzymes to dissolve protein deposits.