Photosystem Il transfers electrons from water to plastoquinone and in the process generates a pH gradient. Plastoquinone (PQ) carries the electrons from PSII to the cytcxhrome bfcomplex. Plæ;toquinone is an analog Of Coenzyme Q. only differences are the methyl groups replacing the methoxy groups Of Q and a variable Isoprenoid tail. Plastoquinone can functions a one or two electron acceptor and donor. When it is fully reduced to PQH2 it is called plastoquinol. Like COQ, PQ isa lipophilic mobile electron carrier carrying electrons from PSII to cytochrome bf. Photosystem Il is homologous to the purple bacterial photoreaction center we talked about previously. PSI' is an integral membrane protein. The core of this membrane protein is formed by subunits DI and m. These two subunits span the membrane and are homologous to subunits L and M of the bacterial photosystem. Of course PSII is more complicated than its prokaryotic counterpart. PSII contains a lot more subunits and additional chlorophylls to achieve a lot higher efficiency than bacterial systems. overall reaction Of PSII is shown 2PQ + 2H20 — 02 +2PQH2

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