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3D rendering of centrioles showing the triplets. In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. [1] Centrioles are found in most eukaryotic cells, but are not present in conifers (), flowering plants (angiosperms) and most fungi, and are only present in the male gametes of charophytes, bryophytes, seedless vascular plants, cycads, and Ginkgo.
In general, each centriole of the centrosome is based on a nine-triplet microtubule assembled in a cartwheel structure, and contains centrin, cenexin and tektin. [10] In many cell types, the centrosome is replaced by a cilium during cellular differentiation. However, once the cell starts to divide, the cilium is replaced again by the centrosome ...
Since the centrosome organizes the microtubules of a cell, it has to do with the formation of the mitotic spindle, polarity and, therefore, cell shape, as well as all other processes having to do with the mitotic spindle. [2] The centriole is the inner core of the centrosome, and its conformation is typically somewhat like that of spokes on a ...
Not all eukaryotic cells have each of the organelles listed below. Exceptional organisms have cells that do not include some organelles (such as mitochondria) that might otherwise be considered universal to eukaryotes. [19] The several plastids including chloroplasts are distributed among some but not all eukaryotes.
The cell wall acts to protect the cell mechanically and chemically from its environment, and is an additional layer of protection to the cell membrane. Different types of cell have cell walls made up of different materials; plant cell walls are primarily made up of cellulose, fungi cell walls are made up of chitin and bacteria cell walls are ...
Flagella may have hairs (mastigonemes), as in many stramenopiles. Their interior is continuous with the cell's cytoplasm. [42] [43] Centrioles are often present, even in cells and groups that do not have flagella, but conifers and flowering plants have neither. They generally occur in groups that give rise to various microtubular roots.
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The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division.