Photosystem II: Difference between revisions

<scene name='Photosystem_II/Chlorophyll_green/4'>Chlorophyll</scene> surround Photosystem II and capture energy from sunlight, exciting electrons.  Chlorophyll are highly conjugated and absorb visible light, along with accessory light harvesting pigments such as <scene name='Photosystem_II/Betacarotene/3'>beta carotene</scene>. Beta carotene absorbs visible light of other wavelengths and also protects Photosystem II by destroying reactive oxygen species that result from this photoexcitation.  [[Image:b-car.svg.png|b-car.svg.png|thumb|right|400px|structure of beta carotene]]  Electrons are passed from chlorophyll to <scene name='Photosystem_II/Pheophytin_purple/5'>pheophytin</scene>.  Pheophytin are very similar to chlorophyll except they  contain 2 H⁺ instead of a Mg²⁺ ion.  From the pheophytin, electrons transferred to <scene name='Photosystem_II/Quinone_pink/4'>plastoquinones</scene>, which are reduced.  Between each pair of quinones, an iron, in red, helps to transfer the electron. These plastoquinones eventually move to a plastoquinone pool which travels to another large protein subunit, cytochrome b ₆/ f.  Eventually these electrons reduce NADP⁺ to NADPH.  Here the <scene name='Photosystem_II/Electron_pathway/3'>electron pathway</scene> through Photosystem II is shown, with '''<FONT COLOR="#F87217">beta-carotenes</FONT>''', '''<FONT COLOR="#571B7e">pheophytins</FONT>''', '''<FONT COLOR="#E42217">iron</FONT>''' and '''<FONT COLOR="#F535AA">plasotoquinones</FONT>'''.

Another important facet of photosystem II is its ability to oxidize water to oxygen with its <scene name='Photosystem_II/Oxygen_evolving_centers/8'>oxygen evolving centers</scene>.  These <scene name='Photosystem_II/Oxygen_evolving_centers/3'>centers</scene> were shown to be cubane-like Mn₃CaO₄cluster linked to a fourth Mn by a mono-μ-oxo bridge. [1]  Purple represents manganese, red represents oxygen and green is for calcium.  Oxidation of water to leaves 2 H ⁺ on the lumenal side of the membrane, helping to establish the proton gradient essential for ATP synthesis in the CF₁CF₀-ATP sythase protein.