Photophosphorylation (Production of ATP)

• The production of ATP is defined by chemiosmotic theory.
• Each thylakoid in the grana is an enclosed chamber in which protons (H+) are pumped from the stroma using proton pumps (protein carriers) located in the thylakoid membranes. The energy for this process comes from the photolysis of water.
• Photolysis also produces protons, further increasing their concentration inside the thylakoid space.
• Due to the high concentration of protons in the thylakoid space and the low concentration of protons in the stroma, protons cross the thylakoid membranes through ATP synthase channel proteins.
• As protons pass through the ATP synthase channel proteins, the structure of the enzyme is altered, allowing ADP + Pi to be catalysed to form ATP.