In bioenergetics, ATP does not fuel endergonic biosynthesis through a separate hydrolysis reaction written alongside it; instead it participates directly by transferring a phosphate group to the substrate, converting a thermodynamically unfavorable step into part of a coupled reaction sequence whose overall Gibbs free energy change is negative. The energy release is localized not in the phosphorylation step itself — stacking mutually repelling phosphate groups is endergonic — but in the subsequent hydrolysis of the displaced pyrophosphate leaving group, which is strongly exergonic and, by removing product, also drives the sequence forward under Le Chatelier's principle. The concept belongs to biochemistry and bioenergetics, and it depends on the separation of thermodynamic control (ΔG) from kinetic control (activation energy): ATP is energetically reactive but kinetically stable, so enzymes that lower activation energy determine when and where cellular energy is spent.
In bioenergetics, ATP does not fuel endergonic biosynthesis through a separate hydrolysis reaction written alongside it; instead it participates directly by transferring a phosphate group to the subs…