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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.
These organisms perform photosynthesis through organelles called chloroplasts and are believed to have originated about 2 billion years ago. [1] Comparing the genes of chloroplast and cyanobacteria strongly suggests that chloroplasts evolved as a result of endosymbiosis with cyanobacteria that gradually lost the genes required to be free-living.
Chloroplasts have many similarities with photosynthetic bacteria, including a circular chromosome, prokaryotic-type ribosome, and similar proteins in the photosynthetic reaction center. [69] [70] The endosymbiotic theory suggests that photosynthetic bacteria were acquired (by endocytosis) by early eukaryotic cells to form the first plant cells ...
Chloroplasts have many similarities with cyanobacteria, including a circular chromosome, prokaryotic-type ribosomes, and similar proteins in the photosynthetic reaction center. [ 204 ] [ 205 ] The endosymbiotic theory suggests that photosynthetic bacteria were acquired (by endocytosis ) by early eukaryotic cells to form the first plant cells.
Not only do all members inside each class share common ancestry, but the two classes also, by means of common structure, appear related. [2] [3] Cyanobacteria, the precursor to chloroplasts found in green plants, have both photosystems with both types of reaction centers. Combining the two systems allows for producing oxygen.
The Type II photosynthetic apparatus in non-oxygenic bacteria consists of light-harvesting protein-pigment complexes LH1 and LH2, which use carotenoid and bacteriochlorophyll as primary donors. [3] LH1 acts as the energy collection hub, temporarily storing it before its transfer to the photosynthetic reaction centre (RC). [ 4 ]
[2] Photosystem II (of cyanobacteria and green plants) is composed of around 20 subunits (depending on the organism) as well as other accessory, light-harvesting proteins. Each photosystem II contains at least 99 cofactors: 35 chlorophyll a, 12 beta-carotene, two pheophytin, two plastoquinone, two heme, one bicarbonate, 20 lipids, the Mn 4 CaO
Green plants and photosynthetic bacteria are photoautotrophs. Photoautotrophic organisms are sometimes referred to as holophytic. [3] Oxygenic photosynthetic organisms use chlorophyll for light-energy capture and oxidize water, "splitting" it into molecular oxygen.