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Schematic model of the major protein complexes involved in photosynthesis
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Summary (more detail below figure): A schematic model (cartroon) detailing the main photosynthetic complexes engaged
in oxygenic photosynthesis situated within the higher plant / green
algal (eukaryotic) thylakoid membrane, where Photosystem Two (PSII) is shown as the first major
complex in the electron transport chain, after light (hv) has been
absorbed by its bound light-harvesting components, the Lhcb proteins. Click
on each complex
within image below to gain more information. Clicking on the PSII
complex will zoom it, and then its individual subunits will become
active for further investigation. |
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A larger version of this image (1800 x 915; 296 kb). |
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A detailed model (July 2010 update) of the Z scheme including structural information on the organisation of the protein complexes involved in electron (e-) and proton (H+) transport within the thylakoid membrane of green plants. The electron transport scheme is based on the literature, numerous reviews / text book figures, as well as numerous valuable discussions with local, national and international colleagues - updated by Jon since 1996. |
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In higher plants (eukaryotes), photosynthetic and carbon fixation reactions are housed in the chloroplasts. The so-called 'light reactions' of photosynthesis take place in the chloroplast's thylakoid membranes and are driven by light, as captured by the Light-Harvesting Complex (LHCI (Lhca) / LHCII (Lhcb)) antenna that are bound to PSI and PSII, respectively. 'Linear electron transport' involves electrons (e-) being derived from the splitting of water, by PSII, and sequentially passed along the photosynthetic e- transport chain by plastoquinone (PQ), cytochrome b6f (Cytb6f), plastocyanin (PC), Photosystem I (PSI) and PSI-bound ferredoxin (Fd), before being used for producting NADPH by ferredoxin–NADP+ oxido-reductase (not shown) in the Stromal matrix (Stroma). From this splitting of water (water oxidation), and from the Q-cycle operating about Cytb6f, protons (H+) accumulate in the thylakoid's lumenal space (lumen), thereby generating a gradient which provides for ATP production by proton motive force (chemiosmosis) via chloroplastic ATP synthase (CFoF1 ATP synthase). Under conditions causing the phenomenon of 'cyclic e- transport' that operates about Photosystem One (PSI), protons H+ are reduced to molecular hydrogen (H2) via hydrogenases (not shown). The products of the above, ATP and NADPH, are consumed during carbon dioxide (CO2) fixation, where a separate enzyme, RuBisCO, is responsible for incorporating CO2 into Ribulose bisphosphate (RuBP), ultimately forming sugar phosphates (our food, the global biomass). |
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see: e.g. Guskov et al., (2009; T. elongatus PSII; cyanobacterial), Standfuss et al., (2005; spinach LHCII; higher plant), Stroebel et al., (2003; Chlamydomonas Cyt b6f; green algal), Jordan et al., (2001; T. elongatus PSI; cyanobacterial) and Amunts et al., (2007; pea LHCI-PSI; higher plant).
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