Catabolism

Catabolism is the set of metabolic pathways which break down molecules into smaller units and release energy. A simpler way to put it: catabolism is the metabolic breakdown of complex molecules into simpler ones, often resulting in a release of energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides and amino acids, respectively. As molecules such as polysaccharides, proteins and nucleic acids are made from long chains of these small monomer units.

People who are undernourished are sometimes said to be in a catabolic state, which means that they are catabolizing their body tissues, without replacing them. Hence, a proper relation between anabolism and catabolism is essential for the maintenance of bodily homeostasis and dynamic equilibrium.

The byproducts of catabolism are cellular wastes, which include lactic acid, acetic acid, carbon dioxide, ammonia, creatinine, and urea. The creation of these wastes is usually an oxidation process involving a release of chemical free energy, some of which is lost as heat, but the rest of which is used to drive the synthesis of adenosine triphosphate (ATP). This molecule acts as a way for the cell to transfer the energy released by catabolism to the energy-requiring reactions that make up anabolism.

Schematic diagram of catabolism