User talk:Cole Faulkner

From Proteopedia

Photosynthetic Pathway

Photosynthesis is the pathway that uses light energy (photons) to drive the production of Adenosine Triphosphate. As photons hit the organism, a small percentage hit the photo-reaction center of P680 (Photosystem II) and P700 (Photosystem I) to excite either P680 (2AXT) or P700 (2O01) which then drives electron transport until the final products are reduced ferradoxin and NADPH.

To excite P680 in photosystem II, four electrons from Yz (electron donor) and four photons interact with P680. This causes electronic excitation of P680 (at nearly -0.8 volts), which then causes a cascade of oxidation-reduction reactions. Furthermore, with each oxidation-reduction reaction, the redox potential increases to nearly +0.4 volts at the end of photosystem II.

The cascade of oxidation-reduction reactions starts off with an electronically excited P680, which donates electrons to a pheophytin acceptor (Ph). From there, the pheophytin acceptor donates electrons to QA (which is a protein-bound plastoquinone), and then QA donates its electrons to QB (another protein-bound plastoquinone). Next, QB donates the electrons to QH2 (reduced plastoquinone), which then donates the electrons to the cytochrome b6f complex. When this occurs, the cytochrome b6f complex donates it electrons to plastocyanin (PC) and also releases eight protons into the thylakoid membrane. Finally, the plastocyanin transfers its electrons to P700 in order to start photosystem I. The overall reaction for photosystem II is 2H2O (with 4 photons excitation)-> 4H+ + 4e- +O2.