What is an enzyme?

An enzyme is known as a biological catalyst. This is because they can speed up reactions by providing an alternative pathway, lowering the activation energy of the reaction. They are normally composed of a protein and a non protein (co-factor). The enzyme has an active site, where the substrate/reactant binds. Enzymes are substrate specific; you can think of this like a "Lock and Key". Only a certain substrate can bind to the active site, just as only a certain key can fit into a lock. Enzymes can be denatured ( their shape changes and the active site no longer works as it it also a different shape) by changing the pH or the temperature of where you find the enzyme.