what is photophosphorylation ? explain the 2 ways this mechanism occuring in the choloroplast ?

Photophosphorylation or photosynthetic phosphorylation is the process of phosphate group transfer into ADP to synthesize energy rich ATP molecule making use of light as external energy source. It is believed that single molecule of ATP is formed from ADP and Pi (inorganic Phosphate) through ATPase complex. 


Photophosphorylation is of two types: 1. Non-Cyclic  2. Cyclic


It is called Non – cyclic when ATP is formed because of protons coming from non-cyclic electron transport system. It involves the participation of both PS I and PS II. Photo oxidation of water occurs and the water splits into H+, e- and release of O2. It occurs in sequence of electron transfers where NADP + is reduced by PS I and PS II and PS II is reduced by water so that electron transport is non cyclic. It is concerned with the production of ATP and reduction of NADP +.


It is called cyclic when ATP are formed as a result of protons coming from electron transport system. It involves participation of only PS I. This is not concerned with photo oxidation of water. The electrons exuded from PS I return back to PS I so that the electron transport is cyclic. It is only concerned with the production of ATP.

  • 7
What are you looking for?