Chemiosmotic hypothesis

1. Proposed by Peter Mitchell

2. The chemiosmotic hypothesis proposes that the ATP synthesis is linked to development of a proton gradient across the thylakoid membrane.

3. As electrons move through the electron transport chain, protons (H+) are transported across the thylakoid membrane leading to the formation of Proton gradient. Here, the proton accumulation is towards the inside of the membrane, i.e., in the lumen.

4. The accumulation of proton creates a gradient of both proton concentration and charge, resulting in generation of the proton motive force across the membrane.

5. Breakdown of this gradient leads to the synthesis of ATP. The ATP synthase enzyme consists of two parts: one called the CF0 is embedded in the thylakoid membrane and forms a transmembrane channel that carries out facilitated diffusion of protons across the membrane. The other portion is called CF1 and protrudes on the outer surface of the thylakoid membrane on the side

6. The gradient is broken down due to the movement of protons across the membrane to the stroma through the transmembrane channel of the CF0 of the ATP synthase.

7. The breakdown of the gradient provides enough energy to cause a conformational change in the CF1 particle of the ATP synthase, that leads to the formation of several molecules of energy packed ATP