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Photosystem I (PSI, or plastocyanin–ferredoxin oxidoreductase) is one of two photosystems in the photosynthetic light reactions of algae, plants, and cyanobacteria. Photosystem I [ 1 ] is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ...
Studies have actually demonstrated that the two wavelengths together have a synergistic effect on the photosynthetic activity, rather than an additive one. [ 1 ] Each photosystem has two parts: a reaction center, where the photochemistry occurs, and an antenna complex , which surrounds the reaction center.
The cyclic light-dependent reactions occur only when the sole photosystem being used is photosystem I. Photosystem I excites electrons which then cycle from the transport protein, ferredoxin (Fd), to the cytochrome complex, b 6 f, to another transport protein, plastocyanin (Pc), and back to photosystem I. A proton gradient is created across the ...
They are transmembrane proteins embedded in the chloroplast thylakoid or bacterial cell membrane. Plants, algae, and cyanobacteria have one type of PRC for each of its two photosystems. Non-oxygenic bacteria, on the other hand, have an RC resembling either the Photosystem I centre (Type I) or the Photosystem II centre (Type II).
Photosystem I contains a pair of chlorophyll a molecules, designated P700, at its reaction center that maximally absorbs 700 nm light. Photosystem II contains P680 chlorophyll that absorbs 680 nm light best (note that these wavelengths correspond to deep red – see the visible spectrum). The P is short for pigment and the number is the ...
In photosynthesis, plastocyanin functions as an electron transfer agent between cytochrome f of the cytochrome b 6 f complex from photosystem II and P700+ from photosystem I. Cytochrome b 6 f complex and P700 + are both membrane-bound proteins with exposed residues on the lumen-side of the thylakoid membrane of chloroplasts. Cytochrome f acts ...
Unlike non-cyclic photophosphorylation, NADP + does not accept the electrons; they are instead sent back to the cytochrome b 6 f complex. [citation needed] In bacterial photosynthesis, a single photosystem is used, and therefore is involved in cyclic photophosphorylation.
Using this cyclic electron chain around photosystem one (PS I), chlororespiration compensates for the lack of light. This cyclic pathway also allows electrons to re-enter the PQ pool through NAD(P)H enzyme activity and production, which is then used to supply ATP molecules (energy) to plant cells. [7]