Question

How does ATP hydrolysis release energy?

Answer 1

ATP stands for Adenosine triphosphate. ATP is the energy currency used in cellular processes. It is used to provide energy to both the energy-consuming as well as energy-releasing reactions, as a small amount of energy is required as activation energy in the energy-releasing reactions also.

Complete answer:
For energy to be released from ATP, the chemical bonds are broken down. Thus, the more will be the bonds, the more energy the molecule contains. These bonds are reformed as easily as they are broken down, hence ATP acts like a rechargeable battery that provides energy to the cellular processes.
ATP is composed of an adenosine molecule (nucleoside) bound to three phosphate groups. The three phosphate groups starting from the one closest to ribose sugar are named alpha, beta, and gamma. When the bond between the two phosphate groups (beta and gamma) is broken, adenosine diphosphate (ADP) and an inorganic phosphate group (Pi) are produced, and free energy is released. This reaction of releasing free energy along with the production of ADP and Pi is known as hydrolysis. In hydrolysis, one molecule of water is consumed.
Hydrolysis is a reversible reaction. The ADP and Pi can also get combined to regenerate ATP and it requires the input of energy. For every molecule of ADP produced from ATP, 7.3 kcal/mole (30.5kJ/mol) is released under standard conditions. But in a living cell, the amount of free energy released is doubled (14 kcal/mole).

Note: The ATP molecule is highly unstable and dissociates spontaneously into ADP and Pi, so if not used immediately, the free energy is lost as heat. Alpha, Beta and gamma are the three phosphate groups which tend to initiate from one closest to ribose sugar.