Phosphorus (P) is an essential mineral that is found in all cells within the body. The body of the human adult contains about 400-500 g. The greatest amount of body phosphorus can be found primarily in bone (85%) and muscle (14%). Phosphorus is primarily found as phosphate (PO₄ ^2-). The major building blocks of biology are covalent molecules comprising proteins, polysaccharides, and nucleic acids. The nucleic acids deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are polymers based on phosphate ester monomers. The high-energy phosphate bond of ATP is the major energy currency of living organisms. Cell membranes are composed largely of phospholipids. The inorganic constituents of bone are primarily a calcium phosphate salt called hydroxyapatite. A variety of enzymatic activities are controlled by alternate phosphorylation and dephosphorylation of proteins. The metabolism of all major metabolic substrates depends on the functioning of phosphorus as a cofactor in a variety of enzymes and as the principal reservoir for metabolic energy.