How does energy coupling work?

Energy coupling occurs when the energy released by exergonic reactions is used to drive an endergonic reaction. More specifically, cells often couple the exergonic reaction of ATP hydrolysis with the endergonic reactions of cellular processes. For example, transmembrane ion pumps in nerve cells utilize energy from ATP to pump ions across the membrane and gain free energy. The sodium-potassium pump pushes sodium of the cell and potassium into the cell. By donating free energy to the sodium-potassium pump, phosphorylation drives the endergonic reaction.