![]() ![]() The two photosystems performing all of this magic are protein complexes that are similar in structure and means of operation. Energy for the entire process came from four photons of light. The electrons have made their way from water to NADPH via carriers in the thylakoid membrane and their movement has released sufficient energy to make ATP. At this point, the light cycle is complete - water has been oxidized, ATP has been created, and NADPH has been made. Note that reduction of NADP+ to NADPH requires two electrons and one proton, so the four electrons and two protons from oxidation of water will result in production of two molecules of NADPH. Ferredoxin then passes the electron off to the last protein in the system known as Ferredoxin:NADP+ oxidoreductase, which gives the electron and a proton to NADP+, creating NADPH. ![]() Meanwhile, the excited electron from PS I passes through an iron-sulfur protein, which gives the electron to ferredoxin (another iron sulfur protein). PS I gains a positive charge as a result of the loss of an excited electron and pulls the electron in plastocyanin away from it. With absorption of a photon of light by PS I, a process begins, that is similar to the process in PS II. Cb6f drops the electron off at plastocyanin, which holds it until the next excitation process begins with absorption of another photon of light at 700 nm by PS I. ATP synthase makes ATP from the proton gradient created in this way. PQH2 passes these to the Cytochrome b6f complex (Cb6f) which uses passage of electrons through it to pump protons into the thylakoid space. ![]()
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