Cellular metabolism is represented by a large number of metabolic reactions involving the conversion of the carbon source (usually glucose) into the building blocks needed for macromolecular biosynthesis. These reactions form metabolic networks within cells. These networks can then be used to study metabolism within cells.
To allow these networks to interact, a tight connection between them is necessary. This connection is provided by usage of common cofactors such as ATP, ADP, NADH and NADPH. In addition to this, sharing of some metabolites between the different networks further tightens the connections between the different networks.