The energy released from ATP occurs when

• A. The bonds of ATP are broken
• B. The bonds of ATP are formed
• C. ATP is hydrolyzed to AMP only
• D. Phosphate groups are removed without breaking bonds

Answer: (A)

Energy stored in ATP is in the high-energy bonds between the phosphate groups. The energy is released when one of these bonds is broken during hydrolysis, yielding products like ADP and inorganic phosphate. This bond breakage releases energy that the cell can use for work, rather than energy being released by forming bonds. If phosphate groups were removed without breaking bonds, or if the reaction relied on forming bonds instead of breaking them, little to no usable energy would be liberated. While hydrolysis to AMP and PPi is another possible pathway, the key idea is that the energy comes from breaking the phosphoanhydride bond in ATP during hydrolysis.