This hypothesis was proposed by P. Mitchell in 1961. Photosynthesis and respiration both processes are involved in the synthesis of ATP. Electron transport in both photosynthesis and respiratiosn creates proton gradient inside the thylakoid or in the outer chamber of the mitochondria respectively. The movement of hydrogen ions from high proton concentration to lower proton concentration and an electrochemical concentration gradient of proton synthesize the ATP with the help of enzyme ATPase. Three important events during photosynthesis are associated to create proton gradient inside the thylakoid. These are :-
i) Lumen of thylakoid become enriched with hydrogen ions (H+) due to photolysis of water.
ii) Primary acceptor of electron is present on the outer side of the thylakoid and it transfer electron to the H-carrier. This H-carrier removes proton from the matrix while transporting electron to the inner side of the membrane. The proton is released into the lumen and electron passes to the next carrier.
iii) NADP reductase present on the outerside of thylakoid membrane obtains electron from the PS I and H+ ions from the matrix to reduce NADP+ to NADPH.
These three events constantly helps in increasing of proton concentration inside the lumen of thylakoid and decreases proton concentration in the matrix of chloroplast. A proton gradient develops across the thylakoid and proton movements from higher concentration to lower concentration through special channels ( CF0 - CF1 ) activates the enzyme ATPase will make the ATP from ADP. Because movement of proton is from higher to lower concentration like water moement in osmosis this process is named as chemiosmosis synthesis of ATP.
i) Lumen of thylakoid become enriched with hydrogen ions (H+) due to photolysis of water.
ii) Primary acceptor of electron is present on the outer side of the thylakoid and it transfer electron to the H-carrier. This H-carrier removes proton from the matrix while transporting electron to the inner side of the membrane. The proton is released into the lumen and electron passes to the next carrier.
iii) NADP reductase present on the outerside of thylakoid membrane obtains electron from the PS I and H+ ions from the matrix to reduce NADP+ to NADPH.
These three events constantly helps in increasing of proton concentration inside the lumen of thylakoid and decreases proton concentration in the matrix of chloroplast. A proton gradient develops across the thylakoid and proton movements from higher concentration to lower concentration through special channels ( CF0 - CF1 ) activates the enzyme ATPase will make the ATP from ADP. Because movement of proton is from higher to lower concentration like water moement in osmosis this process is named as chemiosmosis synthesis of ATP.
Mechanism of chemiosmotic synthesis of ATP in chloroplast
