Energy is released from ATP primarily through the hydrolysis of its high- energy phosphate bonds, specifically the bond between the second and third phosphate groups (phosphoanhydride bond). When ATP undergoes hydrolysis, a water molecule breaks this bond, resulting in the removal of one phosphate group and the formation of adenosine diphosphate (ADP) and an inorganic phosphate (Pi). This reaction releases energy that the cell can use for various biological processes
. The key to energy release lies not in the breaking of the bond itself-since breaking bonds requires energy-but in the formation of new, more stable bonds in the products (ADP and Pi). The products have lower free energy due to factors such as resonance stabilization of the inorganic phosphate and reduced electrostatic repulsion between phosphate groups, making the overall reaction exergonic (energy-releasing)
. The standard free energy change (∆G) for ATP hydrolysis is about −7.3 kcal/mol under standard conditions, but in cells, it can be as much as −14 kcal/mol due to cellular conditions. This energy is harnessed through a process called energy coupling, where the energy released from ATP hydrolysis drives endergonic (energy-requiring) reactions, such as muscle contraction, active transport across membranes (e.g., the sodium-potassium pump), and biosynthesis
. In summary:
- ATP hydrolysis breaks a high-energy phosphoanhydride bond via water addition (hydrolysis).
- This produces ADP and inorganic phosphate (Pi).
- Energy is released because the products are more stable and have lower free energy than ATP.
- The released energy is used by cells to perform work through energy coupling mechanisms.
This process is essential for cellular metabolism and energy transfer
