non-cyclic photophosphorylation

• Non-cyclic photophosphorylation involves both photosystems
• light is absorbed by photosystem 2 (located in thylakoid membrane) and passed to photosystem 2 primary pigment (P680)
• electron in primary pigment molecule (chlorophyll molecule) is excited at a higher energy level (photoactivation)
• excited electron is passed down a chain of electron carriers known as an ETC, before being passed onto photosystem 1
• During this process, ADP and inorganic phosphate are synthesized into ATP by chemiosmosis
• ATP is then passed to light independant reactions
• Photosystem 2 contains a water splitting enyme
• Catalyzed the breakdown of water by light (photolysis)

  • 2H2O -> 4H + 4e + O2
• as excited electrons leave primary pigment of photosystem 2 and passed onto photosystem 1 they are replaced by electrons by photolysis of water
• At the same time as the photoactivation of electrons in photosystem 2, electrons in photosystem1 are also undergoing photoactivation
• these electrons from photosystem 1 also pass along an ETC, combine with hydrogen ions (produced by photolysis) and the carrier molecule NADP to produce reduced NADP
• Equation for reduced NADP in photosystem 1

  
• the reduced NADP are then passed to light independent reactions to be used in the synthesis of carbohydrates
• non-cyclic phosphorylation