Schematic breakdown of largebiomolecules to release energy for fueling thecellmetabolism by producingATP, the energy currency of the cellCarbon Catabolism pathway map for free energy including carbohydrate and lipid sources of energy
Cells use the monomers released from breaking down polymers to either construct new polymer molecules or degrade the monomers further to simple waste products, releasing energy. Cellular wastes includelactic acid,acetic acid,carbon dioxide,ammonia, andurea. The formation of these wastes is usually anoxidation process involving a release of chemical free energy, some of which is lost asheat, but the rest of which is used to drive the synthesis ofadenosine 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 upanabolism.
There are many signals that control catabolism. Most of the known signals arehormones and the molecules involved in metabolism itself.Endocrinologists have traditionally classified many of the hormones asanabolic or catabolic, depending on which part of metabolism they stimulate. The so-called classic catabolic hormones known since the early 20th century arecortisol,glucagon, andadrenaline (and othercatecholamines). In recent decades, many more hormones with at least some catabolic effects have been discovered, includingcytokines,orexin (known ashypocretin), andmelatonin.[citation needed]
Released from alpha cells in thepancreas either when starving or when the body needs to generate additional energy; it stimulates the breakdown ofglycogen in theliver to increase blood glucose levels; its effect is the opposite ofinsulin; glucagon and insulin are a part of anegative-feedback system that stabilizes blood glucose levels.
