A metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical reactions catalysed by enzymes. In most cases a metabolic pathway, the product of one enzyme acts as the substrate for the next. However, set products are considered waste and removed from the cell. These enzymes often require dietary minerals, vitamins, and other cofactors to function.