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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 ferredoxin. Ultimately, the electrons that are transferred by Photosystem I are used to produce the moderate-energy hydrogen carrier NADPH. [2]
Reaction centers are present in all green plants, algae, and many bacteria.A variety in light-harvesting complexes exist across the photosynthetic species. Green plants and algae have two different types of reaction centers that are part of larger supercomplexes known as P700 in Photosystem I and P680 in Photosystem II.
Carbon on Earth naturally occurs in two stable isotopes, with 98.9% in the form of 12 C and 1.1% in 13 C. [1] [8] The ratio between these isotopes varies in biological organisms due to metabolic processes that selectively use one carbon isotope over the other, or "fractionate" carbon through kinetic or thermodynamic effects. [1]
P870 → P870 * → ubiquinone → cyt bc 1 → cyt c 2 → P870. This is a cyclic process in which electrons are removed from an excited chlorophyll molecule (bacteriochlorophyll; P870), passed through an electron transport chain to a proton pump (cytochrome bc 1 complex; similar to the chloroplastic one), and then returned to the chlorophyll ...
Photosynthesis (/ ˌ f oʊ t ə ˈ s ɪ n θ ə s ɪ s / FOH-tə-SINTH-ə-sis) [1] is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabolism.
The electron transfers from pheophytin to plastoquinone (PQ), which takes 2e-(in two steps) from pheophytin, and two H + Ions from the stroma to form PQH 2. This plastoquinol is later oxidized back to PQ, releasing the 2e - to the cytochrome b 6 f complex and the two H + ions into the thylakoid lumen .
The reaction center initiates a complex series of chemical reactions that capture energy in the form of chemical bonds. For photosystem II, when either of the two chlorophyll a molecules at the reaction center absorb energy, an electron is excited and transferred to an electron acceptor molecule, pheophytin , leaving the chlorophyll a in an ...
Oxygenic photosynthesis can be performed by plants and cyanobacteria; cyanobacteria are believed to be the progenitors of the photosystem-containing chloroplasts of eukaryotes. Photosynthetic bacteria that cannot produce oxygen have only one photosystem, which is similar to either PSI or PSII .