define photophosphorylaytion &describ noncyclic photophosphorylation

Photo-Phosphorylation

• The process of formation of ATP in chloroplast in the presence of sunlight

• Photo-phosphorylation is of two types:

  • Non-cyclic photo-phosphorylation

  • Cyclic photo-phosphorylation

Non-Cyclic Photo-Phosphorylation

• 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.

• 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 NADP⁺ 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.