An enzyme is a biological catalyst and is almost always a protein. It speeds up the rate of a specific chemical reaction in the cell. The enzyme is not destroyed during the reaction and is used over and over. A cell contains thousands of different types of enzyme molecules, each specific to a particular chemical reaction.
An enzyme is a biological catalyst that is usually a protein but could be RNA. The point of a catalyst is to increase the speed with which a reaction happens. And there are many, many enzymes that are encoded by the genome to make proteins or RNAs that speed up various chemical reactions to do thousands of different functions inside a cell.- Christopher P. Austin, M.D.