Glucose is the major energy source for mammalian cells as well as an important substrate for protein and lipid synthesis. It enters from extracellular fluid into the cell through two distinct families of structurally related glucose transporters. Once in the cells, glucose is transformed through the Glycolysis generic pathway.

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Pyruvic acid can also be the initial substrate of the glycolysis reverse reaction, namely Gluconeogenesis (often associated with Ketosis) that plays a crucial role in maintaining glucose homeostasis.

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The pentose phosphate pathway (PPP) is the major source for NADPH that is strongly required for anabolic processes. Because of its structure, NADPH readily donates hydrogen ions to metabolites thus reducing them and making them available for energy harvest at a later time.