Energy coupling
Energy transformations obey thermodynamics. Exergonic reactions release free energy; endergonic reactions require input. Cells couple reactions so the overall ΔG is negative. ATP can transfer a phosphate to a reactant or protein, changing reactivity or conformation. Energy is released by the net formation of more stable products during ATP hydrolysis, not simply by breaking a bond.
MAKE IT CONCRETE
A transport protein couples ATP hydrolysis to moving ions against their electrochemical gradient.
DON’T FALL FOR THIS
Breaking a bond requires energy. ATP hydrolysis releases net energy because of the full reaction.