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Tubulin and microtubule-mediated processes, like cell locomotion, were seen by early microscopists, like Leeuwenhoek (1677). However, the fibrous nature of flagella and other structures were discovered two centuries later, with improved light microscopes, and confirmed in the 20th century with the electron microscope and biochemical studies.
In molecular biology, an axoneme, also called an axial filament, is the microtubule-based cytoskeletal structure that forms the core of a cilium or flagellum. [1] [2] Cilia and flagella are found on many cells, organisms, and microorganisms, to provide motility.
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.
In the cell apex is the basal body that is the anchoring site for a flagellum. Basal bodies originate from and have a substructure similar to that of centrioles, with nine peripheral microtubule triplets (see structure at bottom center of image). The "9+2" structure is visible in this cross-section micrograph of an axoneme.
Microtubule-based: Similar to neurons and dendritic cells, microtubules form the main structural core of primary processes of podocytes. [21] In addition, oligodendrocytes possess two distinct types of microtubules: [ 22 ]
Longitudinal section through the flagella area in Chlamydomonas reinhardtii. In the cell apex is the basal body that is the anchoring site for a flagellum. Basal bodies originate from and have a substructure similar to that of centrioles, with nine peripheral microtubule triplets (see structure at bottom center of image).
The axoneme of a primary cilium typically has a ring of nine outer microtubule doublets (called a 9+0 axoneme), and the axoneme of a motile cilium has, in addition to the nine outer doublets, two central microtubule singlets (called a 9+2 axoneme). This is the same axoneme type of the flagellum.
The radial spoke is a multi-unit protein structure found in the axonemes of eukaryotic cilia and flagella. [1] Although experiments have determined the importance of the radial spoke in the proper function of these organelles, its structure and mode of action remain poorly understood.