Answer:
A substance that speeds up a chemical reaction—without being a reactant—is called a catalyst. The catalysts for biochemical reactions that happen in living organisms are called enzymes. Enzymes are usually proteins, though some ribonucleic acid (RNA) molecules act as enzymes too.
ExplanatioEnzymes perform the critical task of lowering a reaction's activation energy—that is, the amount of energy that must be put in for the reaction to begin. Enzymes work by binding to reactant molecules and holding them in such a way that the chemical bond-breaking and bond-forming processes take place more readily.
Reaction coordinate diagram showing the course of a reaction with and without a catalyst. With the catalyst, the activation energy is lower than without. However, the catalyst does not change the ∆G for the reaction.
Active sites and substrate specificity
To catalyze a reaction, an enzyme will grab on (bind) to one or more reactant molecules. These molecules are the enzyme's substrates.
In some reactions, one substrate is broken down into multiple products. In others, two substrates come together to create one larger molecule or to swap pieces. In fact, whatever type of biological reaction you can think of, there is probably an enzyme to speed it up!
The part of the enzyme where the substrate binds is called the active site (since that’s where the catalytic “action” happens