Coupled reactions in bioenergetics
Start with the big picture
A coupled process proceeds when the free-energy changes of its linked reactions sum to a negative net ΔG. In coupled sequences, standard free-energy changes are additive, whereas equilibrium constants multiply. ATP hydrolysis is a major energy donor, and high-energy intermediates can also support phosphoryl transfer. Cells maintain a high phosphorylation potential to strengthen ATP’s driving force. Enzymes connect reaction steps, while group-transfer, redox, chemiosmotic, and ion-gradient mechanisms link favorable events to biosynthesis, energy conversion, or transport. The relationship ΔG = ΔG°′ + RT ln Q also applies: changes in reactant and product concentrations can affect reaction direction. Together, these ideas explain how cells coordinate energy-requiring processes without treating each reaction in isolation.
What you'll learn
- Explain how linking exergonic and endergonic steps can produce a negative net ΔG.
- Distinguish how ΔG°′ values and equilibrium constants combine in coupled sequences.
- Describe the roles of ATP, high-energy intermediates, and phosphorylation potential.
- Compare group-transfer, redox, chemiosmotic, and ion-gradient coupling.
- Relate reaction quotient changes and enzyme organization to reaction direction and coupling.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
