A First Look at MetabolismMetabolism can be subdivided into two major categories:‧Catabolism (異化反應)-those processes in which complex substances are degradedto simpler molecules. ‧Anabolism(同化反應)-those processes concerned primarily with the synthesis of complex organic molecules.‧Catabolismis generally accompanied by the net release of chemical energy.‧Anabolismrequires a net input of chemical energy. ‧These two sets of reactions are coupled together by ATP.