Metabolism is the set of life-sustaining chemical reactions that take place within each cell of the body.
Metabolism has three functions: turning food into energy, turning food to building blocks for proteins, lipids, carbohydrates and DNA; and eliminating nitrogenous wastes. These reactions play a major role in growth, reproduction, maintenance and in the organisms’ response to environmental stimuli.
The chemical reactions of metabolisms are organized into metabolic pathways in which one compound is turned through a series of steps into another chemical, each step being catalyzed by a specific enzyme. Metabolic reactions can be separated into anabolic reactions, which allow for the synthesis of chemical molecules, and catabolic reactions, which consist in the breaking down of compounds. The carbohydrates constitute the main source of energy for all living organisms. An example of a catabolic reaction is when a cell takes a molecule of glucose and breaks it down to release energy. After the energy has been released, it is captured and stored in a specialized molecule: the adenosine triphosphate or ATP.