Photosystems in Plant Cells: Transferring Excited Electron Energy

[mahela007]

How is the energy of an excited electron sent to another adjacent molecule as in the photosystem of chloroplasts in plant cells?

 

[alxm]

Depends on which exact part you mean. Within PS2 it gets transferred between amino acid resides (e.g. Tyrosine) and on to reduce plastoquinone, which is what serves as the 'electron transport' to the next enzyme in the chain.

Electrons can't be allowed to move freely in the solution/cytoplasm, or they'd zoom off and reduce whatever was most reducible. So you have all these electron-transporting molecules and enzymes, to make sure the right electron goes to the right place.

 

[mahela007]

Thanks for your reply... I'm talking about the antenna complex which "funnels" light energy to the reaction center chlorophyll.. how is energy transferred from one chlorophyll to another adjacent chlorophyll? The electron isn't physically transferred.. I'm interested in knowing how the energy of an excited electron is handed over to a separate molecule..

 

[alxm]

The electron is physically transferred. The excitation from light kicks out an electron from the chlorophyll P680, which goes off to pheophytin.

P680+ then gets an electron from a tyrosine, which in turn gets it from a cluster of manganese ions in the oxygen-evolving complex. Four photons makes for four electrons which results in two water molecules being reduced to an oxygen molecule.

 

[mahela007]

my textbook says the electron is not transferred... :-|