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Euglena gracilis is a freshwater species of single-celled alga in the genus Euglena. It has secondary chloroplasts , and is a mixotroph able to feed by photosynthesis or phagocytosis . It has a highly flexible cell surface, allowing it to change shape from a thin cell up to 100 μm long to a sphere of approximately 20 μm.
Euglena is a genus of single cell flagellate eukaryotes. It is the best known and most widely studied member of the class Euglenoidea, a diverse group containing some 54 genera and at least 200 species. [1] [2] Species of Euglena are found in fresh water and salt water.
Schematic representation of a Euglena cell with red eyespot (9) Schematic representation of a Chlamydomonas cell with chloroplast eyespot (4). The eyespot apparatus (or stigma) is a photoreceptive organelle found in the flagellate or (motile) cells of green algae and other unicellular photosynthetic organisms such as euglenids.
This was also significant for being the first 3D crystal structure of any membrane protein complex. Four different subunits were found to be important for the function of the photosynthetic reaction center. The L and M subunits, shown in blue and purple in the image of the structure, both span the lipid bilayer of the plasma membrane.
A monophyletic subgroup known as Euglenophyceae have chloroplasts and produce their own food through photosynthesis. [ 3 ] [ 4 ] [ 5 ] This group contains the carbohydrate paramylon . Euglenids split from other Euglenozoa (a larger group of flagellates) more than a billion years ago.
It is composed of three protein subunits, OEE1 (PsbO), OEE2 (PsbP) and OEE3 (PsbQ); a fourth PsbR peptide is associated nearby. The first structural model of the oxygen-evolving complex was solved using X-ray crystallography from frozen protein crystals with a resolution of 3.8 Å in 2001. [ 7 ]
Light-dependent reactions of photosynthesis at the thylakoid membrane. Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons.
However, PSII has an additional function over the bacterial system. At the oxidising side of PSII, a redox-active residue in the D1 protein reduces P680, the oxidised tyrosine then withdrawing electrons from a manganese cluster, which in turn withdraw electrons from water, leading to the splitting of water and the formation of molecular oxygen.