Definition for Phosphate
From Biology Forums Dictionary
In biological molecules, phosphorus occurs mainly in the form of acidic phosphate groups.
Phosphorus normally has a valence of 5. Its most common functional group in organic molecules is as a phosphate group (symbolized as -PO42-). Phosphorus is covalently paired to 4 oxygen atoms in phosphate groups: one P=O bond and three P-O- bonds.
In molecular models, phosphorus atoms are represented by orange spheres.
The compound H3PO4 is phosphoric acid, a strong acid that ionizes readily to give H2PO4- and hydrogen ion (H+). This compound can further ionize to HPO42- and H+, and still further to PO43- and H+.
Phosphate group Although all these chemical forms coexist in equilibrium in water, the convention in biology is to represent the phosphate ion in its doubly charged form HPO43-, often abbreviated by the symbol Pi, "inorganic phosphate." This form is shown in the figure to the right.
Phosphate groups are found in DNA and RNA, and in certain lipids. They are involved in the biological storage and release of energy.