question_answer 45)

  Explain how during light reaction of photosynthesis, ATP synthesis is a chemiosmotic phenomenon.

Answer:

                  In light reaction plants trap solar radiation by photosynthetic pigments which convert light energy into chemical energy. Main event pi light reaction is photophosphorylation, i.e., formation of ATP from ADP + Pi by using energy of excited electron movement through electron transport chain, present in thylakoid membrane. Chemiosmosis is the movement of ions across a selectively permeable membrane, down the electrochemical/ proton gradient. Chemiosmosis hypothesis of ATP formation was first proposed by Mitchell (1961) according to which the enzyme ATP synthase generales ATP via a membrane, proton pump and proton gradient. ATP synthase allows ions protons to pass through membrane and proton pump. This creates a high cocentration of protons  in the lumen and hence diffuses across the membrane to activate ATPase, releasing ATP molecules. One molecule of ATP is released for every two  ions passing Through ATPase.