Weight loss Chocolate [Free Box]

 

 

Weight loss Chocolate [Free Box]

 

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  The process starts when light is absorbed by two BChl molecules (a dimer) that lie near the periplasmic side of the membrane. This pair of chlorophyll molecules, often called the "special pair", absorbs photons between 870 nm and 960 nm, depending on the species and, thus, is called P870 (for the species rhodobacter sphaeroides) or P960 (for rhodopseudomonas viridis), with P standing for "pigment"). Once P absorbs a photon, it ejects an electron, which is transferred through another molecule of Bchl to the BPh in the L subunit. This initial charge separation yields a positive charge on P and a negative charge on the BPh. This process takes place in 10 picoseconds (10−11 seconds). The charges on the specialpair + and the BPh− could undergo charge recombination in this state. This would waste the high-energy electron and convert the absorbed light energy into heat. Several factors of the reaction center structure serve to prevent this. First, the transfer of an electron from BPh− to P960+ is relatively slow compared to two other redox reactions in the reaction center. The faster reactions involve the transfer of an electron from BPh− (BPh− is oxidised to BPh) to the electron acceptor quinone (QA), and the transfer of an electron to P960+ (P960+ is reduced to P960) from a heme in the cytochrome subunit above the reaction center. The high-energy electron that resides on the tightly bound quinone molecule QA is transferred to an exchangeable quinone molecule QB. This molecule is loosely associated with the protein and is fairly easy to detach. Two of the high-energy electrons are required to fully reduce QB to QH2, taking up two protons from the cytoplasm in the process. The reduced quinone QH2 diffuses through the membrane to another protein complex (cytochrome bc1-complex) where it is oxidised. In the process the reducing power of the QH2 is used to pump protons across the membrane to the periplasmic space. The electrons from the cytochrome bc1-complex are then transferred through a soluble cytochrome c intermediate, called cytochrome c2, in the periplasm to the cytochrome subunit. Thus, the flow of electrons in this system is cyclical.