Most of the energy in ATP (adenosine triphosphate) is stored in the high-energy phosphate bonds, specifically the two terminal phosphate groups. These bonds are called phosphoanhydride bonds. When ATP is hydrolyzed, one of these phosphate groups is removed, releasing energy that the cell can use for various processes.
The phosphate group that is cleaved off is often referred to as the gamma phosphate, which is the third phosphate in the ATP molecule. The release of this phosphate group converts ATP to ADP (adenosine diphosphate) and inorganic phosphate (Pi), and this reaction is highly exergonic, meaning it releases a significant amount of energy.
This energy is crucial for cellular functions, including muscle contraction, nerve impulse propagation, and biosynthesis of macromolecules. Thus, while ATP as a whole serves as an energy currency in cells, it’s the specific bonds between its phosphate groups that hold the key to its energy storage capabilities.