Question

Describe the mechanism used by plants to shuttle electrons from PSII to PSI.

Please be specific about its biochemical pathway!

Answer 1

The chlorophylls along with some proteins make the photosystems and theses photosystems helps in performing photophosphorylation of the photosynthesis in which ATP are formed from ADP and the final product of it is the NADPH which enters the Calvin cycle to complete the photosynthesis process.

There are two photosystems, Photosystem 1 and photosystem 2. These photosystems when receive light energy that is photons, they release electrons to travel through a electron transport chain. There are reaction center in each photosystem which releases electrons on receiving photons.

The reaction center of PS 1 and PS 2 are known as P700 and P680 respectively. When the PS 2 gets photon, the reaction center of it, the P680 gets excited releasing an electron to the electron transport chain. In the electron transport chain these released electrons from the PS 2 is first accepted by Quinone(Q). Than it is transferred subsequently to a small organic molecule plastoquinone (PQ), then to a cytochrome complex ( Cyt) and finally to a copper containing protein called Plastocyanin (Pc). During the traveling of the electron in the electron transport chain, the energy of electron subsequently going on decreasing. This released energy is used in production of ATP from ADP.

From Pc, the electron reaches to PS1, where it excites the reaction center P700 of it and then the electron reaches to a protein called ferredoxin (Fd). From Gd to enzyme NADP +reductase and than to electron carrier NADP + to synthesize NADPH which is used in Calvin cycle.

The whole process of electron transfer from PS 2 to PS 1 and the production of NADPH is known as non-cyclic photophosphorylation.