Enzymes are proteins that act as catalysts for biological reactions. They speed up chemical reactions by lowering the activation energy required for the reaction to occur. Enzymes do not alter the overall energy of the reaction or the final equilibrium state, but they do increase the rate at which the reaction occurs, allowing biological processes to occur much more quickly and efficiently. Enzymes are essential for many metabolic processes in the body, such as digestion, energy production, and DNA replication.