It is the biosynthetic reaction involving the formation of complex molecules from simpler precursors. For the synthesis of a large variety of complex molecules, the starting materials are relatively few. These include pyruvate, acetyl-CoA, and the intermediates of citric acid cycle. Besides the availability of precursors, the anabolic reactions depend on the supply of energy (as ATP or GTP) and reducing equivalents as (NADPH + H⁺).