Non - Cyclic Photophosphorylation

Non-cyclic photophosphorylation:

It involves photosystem I as well as photosystem II. Both these systems absorb light photons. For convenience, the non-cyclic photophosphorylation is described here in following steps:

(i) When P₆₈₀ absorbs a photon of red light, it gives out an electron, and thus becomes positively charged. This electron from P₆₈₀ passes to P₇₀₀ through a series of electron carriers, like Phaeophytin (Primary acceptor), plastoquinone, cytochrome b₆-f complex, plastocyanin.

This movement of electron is downhill in terms of redox potential scale.

In this series, enough energy is released when the electron is transferred from PQ to cytochrome b₆-f complex. It is utilized to synthesize ATP.

(ii) Simultaneously, electron in the reaction centre of PS I also get excited when they receive red light of 700 nm and these electrons are transferred to another receptor having high redox potential. These electrons then move downhill again, this time to a molecule of NADP⁺. This addition of electron and a proton, reduce it to NADPH + H⁺.

1.The process requires an external electron donor.

2.It is connected with photolysis of water and liberation of oxygen.

3.It is not only connected with ATP synthesis, but also with production of NADPH.

4.Non-cydic photophosphorylation takes place under optimum light, aerobic conditions and in the presence of carbon dioxide.

5.The system is connected with CO2 fixation.

6.It occurs in the granal thylakoids.

7.DCMU inhibits noncyclic photophospho- rylation.