Where is energy stored in a molecule of ATP?

• A. In the bonds connecting the two terminal phosphate groups
• B. In the adenine base
• C. In the ribose sugar
• D. In the terminal phosphate group itself

Answer: (A)

Energy is stored in the high-energy bonds that connect the phosphate groups in ATP. When ATP is hydrolyzed, the bond between the middle and terminal phosphate (the beta–gamma phosphoanhydride bond) is broken, releasing energy that powers cellular processes. The energy comes from the resulting stability of the products (ADP and inorganic phosphate): the phosphate group becomes more resonance-stabilized, electrostatic repulsion among the phosphate oxygens is reduced, and the products are better solvated by water. The adenine base and the ribose sugar are just the structural framework and do not store usable energy, and the energy isn’t stored in the terminal phosphate group itself but in the bonds between phosphates.