Interactions between the catalyst and the reacting molecules lower the activation energy barrier, and the chemical reaction takes place. The product molecules are released from the surface of the catalyst and the process can begin again. Many inorganic catalysts are metals, with lots of surface area where the reacting molecules can be brought together. Each of these reactions has an activation energy barrier that must be overcome. Cells use catalysts to overcome these activation energy barriers and make their spontaneous reactions take place.
Proteins are long chains of amino acids folded into three dimensional shapes.
Reacting molecules, called substrates interact with a folded part of the surface of the enzyme called the active site. The chemical reaction takes place and the product molecules are formed. The product molecules are released from the active site of the enzyme. The active site on the enzyme is free to bind more reacting, substrate, molecules. Activation energy barriers hold back spontaneous reactions.