Both PS1 and PS2 are involved in non-cyclic photophosphorylation?

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Non-cyclic photophosphorylation take place in the grana lamellae or on the thylakoid membrane of choloroplasts. It involves both PS-I and PS-II.

  • PSII absorbs 680 nm wavelength of red light, causing electrons to become excited and jump into an orbit farther from the nucleus.

  • These electrons are then accepted by an electron acceptor, which sends them to an electron transport system. Here ADP is converted into ATP by the help of ATP synthetase enzyme.

  • Electron transport system transfers the electrons to PSI.

  • Electrons in PSI are simultaneously excited on receiving a wavelength of 700 nm. These electrons are again transferred to another electron acceptor having a greater redox potential.

  • From the electron acceptor, electrons are transferred to the molecule of NADP​+.

  • Addition of these electrons reduces the NAD​+ to NADPH + H+.

  • During this process, electrons move downhill, i.e., towards the systems at greater redox potential.

  • The flow of electrons assumes the shape of the letter ‘Z’ when all carriers are placed according to their redox potential. Hence, the process is called Z scheme.

  • Since the electrons lost by PSII do not come back to it, this process of formation of ATP is called non-cyclic photo-phosphorylation.

 

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