Enzymes are proteins that allow certain chemical reactions to take place much quicker than the reactions would occur on their own. Enzymes function as catalysts, which means that they speed up the rate at which metabolic processes and reactions occur in living organisms. Usually, the processes or reactions are part of a cycle or pathway, with separate reactions at each step. Each step of a pathway or cycle usually requires a specific enzyme. Without the specific enzyme to catalyze a reaction, the cycle or pathway cannot be completed.