Cell Metabolism

Regulation

The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed into another by a sequence of enzymes. Enzymes are crucial to metabolism and allow the fine regulation of metabolic pathways to maintain a constant set of conditions in response to changes in the cell's environment, a process known as homeostasis.

Classification

Cellular metabolism has two distinct divisions: anabolism and catabolism. Anabolism is a constructive metabolic process in which a cell uses energy to construct molecules such as enzymes and nucleic acids and perform other essential life functions. Anabolism involves three basic stages: firstly, the production of precursors such as amino acids, monosaccharides, isoprenoids and nucleotides; secondly, their activation into reactive forms; and thirdly, the assembly of these precursors into complex molecules.

Catabolism is the metabolic process by which the cell breaks down complex molecules. The purpose of catabolic reactions is to provide the energy and components needed by anabolic reactions. Catabolic reactions are normally exothermic and are further subdivided according to their substrate into carbohydrate, fat, and protein catabolism.