Adenosine Triphosphate (ATP), an energy-bearing molecule found in all living cells. Formation of nucleic acids, transmission of nerve impulses, muscle contraction, and many other energy-consuming reactions of metabolism are made possible by the energy in ATP molecules. The energy in ATP is obtained from the breakdown of foods. An ATP molecule is composed of carbon, hydrogen, nitrogen, oxygen, and phosphorus atoms. There are three phosphorus atoms in the molecule. Each of these phosphorus atoms is at the center of an atomic group called a phosphate. The phosphate groups are linked to one another by chemical bonds called phosphate bonds. The energy of ATP is locked in these bonds.