Abstract
A living cell can take up nutrients from its environment and chemically convert these substrates into products that it needs for its survival. The chemical conversion of these products is done by catalyzing so-called metabolic reactions. The whole of metabolic reactions that a cell can catalyze forms its metabolic network, and determines the metabolic versatility of the cell. In this chapter, we will investigate such metabolic networks and we will find that all metabolic capabilities of a cell can be captured in a mathematical space: the flux cone. Moreover, we will show that this flux cone can be decomposed into minimal metabolic modes, called elementary flux modes. To make this more precise: elementary flux modes are the minimal combinations of metabolic reactions out of which all other possible combinations of metabolic reactions that can be steadily catalyzed by a cell can be built. We show some applications of the analysis of a metabolic network through its elementary modes. Despite the benefits of elementary flux mode analysis, it cannot always be done because of its computational complexity, for those cases we describe alternative methods to explore the flux cone.