Definition: Adenine (A) is one of four chemical bases in DNA, with the other three being cytosine (C), guanine (G), and thymine (T). Within the DNA molecule, adenine bases located on one strand form chemical bonds with thymine bases on the opposite strand. The sequence of four DNA bases encodes the cell's genetic instructions. A form of adenine called adenosine triphosphate (ATP) serves as an energy storage molecule and is used to power many chemical reactions within the cell.