Question

All bonds require energy to break, but energy is actually released when bonds are formed. With this in mind, it is incorrect to say from a chemistry perspective that breaking the phosphate off of ATP releases a large amount of energy. So where in the reaction does the energy release actually occur?

Answer 1

The energy release during the ATP to ADP conversion is due to the change in free energy associated with the hydrolysis of the high-energy phosphoanhydride bonds and the relief of electron-electron repulsions in ATP, which is a process called dephosphorylation.

Step-by-step explanation:

The energy released during the conversion of ATP to ADP does not come from simply breaking the bond but rather from the complete process of hydrolysis wherein ATP is converted to ADP and inorganic phosphate. The phosphoanhydride bonds in ATP are high-energy bonds. When these bonds are broken during the hydrolysis reaction (ATP + H₂O → ADP + Pi + free energy), the products have a lower free energy than the reactants, causing a release of energy. The cleavage of ATP's terminal phosphate group relieves electron-electron repulsions due to the negative charges of the phosphate groups, contributing to the energy released.

This process of dephosphorylation - where the terminal phosphate is removed from ATP - is critical for providing the energy to power various cellular functions, such as muscle contraction. Furthermore, in the reverse process, energy is required to add a phosphate group to ADP to reform ATP, emphasizing the fact that bond formation stores energy while bond breaking releases it.