Centrioles: Definition, Structure, Functions and Diagram

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Definition of Centrioles

Near the nucleus, eukaryotic cells include two cylindrical, rod-shaped microtubular structures called centrioles.
They are found in most algal cells (with the exception of red algae), moss cells, some fern cells, and most mammal cells, and lack a limiting membrane and DNA or RNA.
Prokaryotes, red algae, yeast, cone-bearing and flowering plants (conifers and angiosperms), and some non-flagellated or non-ciliated protozoans are all devoid of them (such as amoebae).
During mitosis or meiosis, centrioles form a microtubule spindle, the mitotic apparatus, and are sometimes positioned just under the plasma membrane to create and bear flagella or cilia in flagellated or ciliated cells.
The basal body is the part of a centriole that has a flagellum or cilium.

Figure: Centrioles in Plant Cell, Image Created with Bio Render

Centrioles structure

Centrioles and basal bodies are cylindrical structures with a diameter of 0.15–0.25 um and a length of 0.3–0.7 um, though they can be as short as 0.16 um and as long as 8um.
They can be seen under a light microscope, but only an electron microscope can disclose the complexities of the centriole structure.
In the centrosome, a region near the nucleus, each cell has a pair of centrioles. Members of each pair of centrioles are at right angles to one another.
They are sub-microscopic microtubular sub cylinders with a configuration of nine triplet fibrils with the ability to generate duplicates, astral poles, and basal bodies on their own, without the need for DNA or a membrane covering.
A centriole has nine peripheral fibrils in its whorl. The core is devoid of fibrils. As a result, the configuration is known as 9 + 0. Fibrils run parallel to one other but at a 40-degree inclination. Three sub-fibers make up each fibril. As a result, it’s known as a triplet fibril.
The three sub-fibers are actually microtubules that are connected by their edges and hence share the common walls of 2-3 proto-filaments.
Each sub-fiber is 25 nm in diameter. The three sub-fibers of a triplet fibril are labelled C, A, and B from outside to inside. Due to the sharing of some microfilaments, sub-fiber A is complete with 13 proto-filaments, whereas and sub-fibers are incomplete.
—A proteinaceous linkers join the adjacent triplet fibrils. The hub is a rod-shaped proteinaceous substance found in the core of centrioles. The hub is 2.5 nm in diameter. 9 proteinaceous strands extend from the hub to the periphery triplet fibrils. They’re known as spokes.
Before joining with the A sub-fiber, each spoke has an X thickening. Nearby, there is another thickening called as Y. It is connected to both the X thickening and the C – A linkers via connectives.
The centriole in T.S. has a cartwheel look due to the presence of radial spokes and peripheral fibrils.

Centrioles Functions

The creation of the spindle apparatus, which acts during cell division, is aided by centrioles.
Centrioles are missing in the mitotic process, causing divisional mistakes and delays.
Each cilium or flagellum has a single centriole that serves as the anchor point or basal body.
The production of cilia and flagella is also directed by basal bodies.

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Centrioles Citations

Stephen R. Bolsover, Elizabeth A. Shephard, Hugh A. White, Jeremy S. Hyams (2011). Cell Biology: A short Course (3 ed.).Hoboken,NJ: John Wiley and Sons.
Alberts, B. (2004). Essential cell biology. New York, NY: Garland Science Pub.
Winey, M., & O’Toole, E. (2014). Centriole structure. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 369(1650), 20130457.
http://www.biologydiscussion.com/cell/centrioles/centrioles-structure-and-functions-with-diagram/70541.

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