12.1.3—ATP synthesis

ATP synthesis is the energy-requiring formation of ATP from ADP and inorganic phosphate: ADP + Pi → ATP. Energy released by respiration or another linked reaction is transferred into this phosphorylation step.

1. Provide ADP and Pi: ADP is combined with inorganic phosphate; water is released, so the synthesis step is a condensation reaction.
2. Supply energy: An energy-releasing reaction provides the energy needed to join Pi to ADP. The cell therefore captures released energy in a rechargeable ATP molecule instead of allowing it all to dissipate immediately.
3. Use ATP: ATP can later be hydrolysed where cellular work is required, producing ADP + Pi and releasing energy for coupling.
4. Recycle: Energy-releasing reactions phosphorylate the ADP again. Repeated synthesis and hydrolysis create a reversible ATP/ADP coupling cycle.

Energy release → phosphorylation of ADP → ATP stores transferable chemical potential energy → hydrolysis drives a task → ADP + Pi become available for resynthesis. The cycle explains why cells make ATP as needed rather than build a large ATP store.

ATP synthesis is the phosphorylation step, not a synonym for the entire respiratory pathway. This card does not reconstruct the electron transport chain or full oxidative-phosphorylation sequence; those details belong to the mapped respiration material. Do not reverse the equation when describing hydrolysis.