Where is the energy stored in ATP molecules?

ATP, which stands for Adenosine Triphosphate, is the major energy currency of the cell. The energy in ATP molecules is stored in the high-energy bonds between phosphate groups, specifically known as phosphoanhydride bonds.
ATP consists of an adenine base, a ribose sugar, and three phosphate groups. The last two phosphate bonds (the ones connecting the second and third phosphates, and, to a lesser extent, the first and second) are especially high in energy. When the cell needs energy to perform any work—like muscle contraction, nerve impulse transmission, or chemical synthesis—ATP undergoes hydrolysis. In this process, the terminal phosphate group is broken off, forming ADP (adenosine diphosphate) and inorganic phosphate, and a large amount of energy is released for the cell to use.

So, the energy is primarily stored in the bonds between the phosphate groups, especially the bond between the second (beta) and third (gamma) phosphates. These high-energy phosphate bonds make ATP an excellent molecule for temporary energy storage and quick energy release within cells.