Learn about the body's metabolism

Metabolic reactions may be categorized as catabolic - the breaking down of compounds (for example, of glucose to pyruvate by cellular respiration); or anabolic – the building up (synthesis) of compounds (such as proteins, carbohydrates, lipids, and nucleic acids). Usually, catabolism releases energy and anabolism consumes energy.

The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme.

Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy and will not occur by themselves by coupling them to spontaneous reactions that release energy. Enzymes act as catalysts – they allow a reaction to proceed more rapidly – and they also regulate the rate of a metabolic reaction, for example, in response to changes in the cell's environment or signals from other cells.