Carotenoids energy-transfer sequence

It has been postulated that complexes of electron-transfer proteins in a membrane are of graduated redox-potential. The electron transfer occurs through channels provided by a complex sequence of ligands and bonds are conjugated molecules like carotenoids. These proteins are able to accept electrons from excited Chi on one membrane side (anode) and donate them to an acceptor of more positive redox potential on the other side (cathode). The membrane provides a resistance for an ion current from anode to cathode which closes the electrochemical circuit, and converts excitation energy into chemical free energy AG (Figure 9.4 b). 

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