Coupled Reactions
Two reactions linked through a shared intermediate so that a favourable one drives an unfavourable one.
Formula / equation
ΔG_total = ΔG₁ + ΔG₂ < 0
Unit
kJ/mol
In depth
Coupling works because Gibbs energies are additive: as long as the combined change is negative, the overall process is spontaneous even though one component is not. Essentially all biosynthesis relies on coupling to ATP hydrolysis, and metal extraction couples ore reduction to carbon oxidation.
Examples in the real world
Glucose phosphorylation (+13.8 kJ/mol) coupled to ATP hydrolysis (−30.5 kJ/mol) in the first step of glycolysis.