Enzymes are biological catalysts. These are substances that increase the rate of chemical reactions without being used up.
Enzymes are also proteins that are folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.
If the shape of the enzyme changes, its active site may no longer work. We say the enzyme has been denatured. They can be denatured by high temperatures or extremes of pH.
Learn about the Enzyme Structure and Function at the balance.