11.Which one of the following is not true regarding the release of energy during ATP synthesis through chemiosmosis? It involves: A. Breakdown of electron gradient B. Movement of protons across the Membrane of the stroma C. Reduction of NADP to NADPH2 on the stroma side of the Membrane D. Breakdown of proton gradient
Option A The synthesis of ATP from ADP during light reaction of photosynthesis is called photophosphorylation. Chemiosmotic hypothesis was proposed by Mitchell to explain the synthesis of ATP. Chemiosmosis involves the movement of ions across a biological membrane along the concentration gradient and it helps in the synthesis of ATP. During the light dependent reactions of photosynthesis, there is an accumulation of protons inside the lumen of thylakoids. The number of protons is high inside the lumen of thylakoids when compared to the stroma of chloroplast. This creates a proton gradient and the breakdown of this gradient generates ATP. The gradient is broken down due to the movement of protons across the membrane into the stroma through ATP synthase. The chloroplast ATP synthase has two parts: CF0 located in the thylakoid membrane and CF1 that protrudes on the outer surface of the thylakoid membrane facing the stroma. The CF0 forms a transmembrane channel for the movement of protons due to which energy is released and that causes conformational changes in the CF1 of the enzyme. Utilising this energy, ATP is synthesised from ADP by the enzyme ATP synthase. Hence, the synthesis of ATP by chemiosmosis requires a membrane, a proton pump, a proton gradient and ATP synthase. ATP and NADPH are assimilatory powers produced during light reaction of photosynthesis.
