anabolism, the sequences of enzyme-catalyzed reactions by which relatively complex molecules are formed in living cells from nutrients with relatively simple structures. Anabolic processes, which include the synthesis of such cell components as carbohydrates, proteins, and lipids, require energy in the form of energy-rich compounds (e.g., adenosine triphosphate) that are produced during breakdown processes (see catabolism). In growing cells, anabolic processes dominate over catabolic ones. In nongrowing cells, a balance exists between the two.