ATP synthase is neither a passive facilitated diffusion nor an active transport mechanism. Instead, it is an enzyme that synthesizes ATP from ADP and inorganic phosphate (Pi). This process is driven by the proton gradient across the inner mitochondrial membrane, which is generated by the electron transport chain.
Here’s how it works:
- Proton Gradient: The electron transport chain pumps protons (H⁺) from the mitochondrial matrix into the intermembrane space, creating a proton gradient.
- Chemiosmosis: The protons flow back into the matrix through ATP synthase due to the electrochemical gradient. This flow of protons is called chemiosmosis.
- ATP Synthesis: As the protons pass through ATP synthase, the enzyme uses the energy from this flow to phosphorylate ADP, converting it into ATP.
In summary, ATP synthase is a molecular machine that converts the energy stored in a proton gradient into the chemical energy of ATP. It is not a transport protein but rather an enzyme that facilitates the synthesis of ATP.