ATP is made using the energy from spontaneous catabolic reactions. Some of the energy from them is stored in a proton gradient, which is then converted into the chemical bond energy in ATP. The hydrolysis of ATP, which is very strongly exergonic, can then be added to a non-spontaneous reaction, an endergonic one, to make an overall-exergonic and spontaneous reaction.
Work Step by Step
ATP hydrolysis releases a very large amount of energy, so it can be used to combine with other reactions to drive them forward.