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catabolism(kətăb`əlĭz'əm), subdivision of metabolismmetabolism,
sum of all biochemical processes involved in life. Two subcategories of metabolism are anabolism, the building up of complex organic molecules from simpler precursors, and catabolism, the breakdown of complex substances into simpler molecules, often accompanied by
..... Click the link for more information. involving all degradative chemical reactions in the living cell. Large polymeric molecules such as polysaccharides, nucleic acids, and proteins are first split into their constituent monomeric units, such as amino acids, after which the monomers themselves can be broken down into such simple cellular metabolites as lactic acid, acetic acid, carbon dioxide, ammonia, and urea. The first set of reactions provides the cell with monomers with which it can construct new polymeric molecules. The second set of reactions usually involves the process of oxidation and is accompanied by a release of chemical free energy, not all of which is lost as heat, but is partially conserved through the coupled synthesis of adenosine triphosphateadenosine triphosphate
(ATP) , organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of
..... Click the link for more information. . The hydrolysis of this compound is subsequently used to drive almost every energy-requiring reaction in the cell. Thus catabolism also provides the source of chemical energy necessary for the maintenance of the living cell.
a set of chemical processes constituting the reverse of anabolism.
Catabolic processes are directed toward splitting the complexcompounds that form the structural elements of organs andtissues (proteins, nucleic acids, phospholipids) or that are depos-ited in the organs and tissues as reserve material (fat, glycogen).As a result of catabolism, complex compounds lose their specificproperties and are converted to substances that are partly uti-lized for biosynthesis and partly eliminated from the body (inter-mediate and final products of metabolism).