Final answer:
Hydrolysis of ATP to ADP and Pi releases about 7.3 kcal/mol (-30.5 kJ/mol) under standard conditions but around -14 kcal/mol (-57 kJ/mol) in a living cell. ATP serves as the energy currency, linking energy-releasing to energy-consuming processes through energy coupling, with examples including the Na+/K+ pump.
Step-by-step explanation:
The hydrolysis of ATP (adenosine triphosphate) to form ADP (adenosine diphosphate) and Pi (inorganic phosphate) is a crucial reaction in cells, allowing the release of energy needed for various cellular processes. During ATP hydrolysis, energy is released because the products, ADP and phosphate ion, have less energy than the reactants, ATP and water. The general equation for ATP hydrolysis is ATP + H₂O → ADP + Pi, with an energy release of about 7.3 kcal/mol (-30.5 kJ/mol) under standard conditions. However, within a living cell, the energy released is almost double, approximately -14 kcal/mol (-57 kJ/mol).
ATP acts as the energy currency of the cell, linking energy-releasing reactions, such as catabolism of food, to energy-consuming processes. The energy from ATP hydrolysis is often used in energy coupling to power reactions that would not occur spontaneously, such as the action of the Na⁺/K⁺ pump, which is vital for cellular function. In energy coupling, the exergonic reaction of ATP hydrolysis is used to drive endergonic reactions, which means that the free energy released is invested in another reaction or process, rather than being lost as heat.
Referencing the pyrophosphate bond, the hydrolysis of ATP is a reaction where this high-energy bond is broken, leading to the release of energy. This process is reversible, where ATP can be regenerated from ADP and Pi with the input of free energy. The ATP molecule is highly unstable, and if not immediately used, it spontaneously converts to ADP and Pi with the release of energy. This serves as a way to ensure energy is readily available for cellular work when needed.