Hello, guys, In today’s article we are going to study Centrioles. Like – what are centrioles? What is its structure, functions, Composition, etc. We will know the answers to many such questions today, so let’s start.
What Are Centrioles?
Centrioles are two spindle-shaped or cylindrical bodies that lie at the right angle to each other and are surrounded by a zone of hyaline cytoplasm, the centrosphere. These are present near the nucleus and mostly occupy an apical Position.
Centrioles are found in most algae, bryophytes, ferns, and in all animal cells. Red algae, gymnosperms, and angiosperms as also the non flagellated and nonciliated protozoans do not have centrioles.
Centrioles Structure –
The structure of the centriole is basically the same in all the cells. Its size varies from 150-250 nm (1500-2500 Å) in diameter and 3000-20000 Å in length.
A centriole is formed of nine triplets or microtubules or fibres. These are arranged equidistant in a circle around an imaginary central axis. This space between and around the microtubules is filled with an amorphous electron-dense material.
1. Microtubules –
The triplet microtubules are all identical. Each triplet is composed of three sub fibres, designated as A, B, and C. Each sub-fibre is about 250 Å in diameter. Subfibre A is tubular and its wall is formed of 13 globular subunits. Subfibre B and sub fibre C are C shaped because B shares 3 subunits of sub fibre A and sub fibre C shares 3 subunits of sub fibre B. Each subunit is about 40-45 Å in diameter.
2. Linkers –
The sub fibre A of each triplet is linked with the sub fibre C of the neighbouring triplet by a connection of some dense material. But in some cases, the connection may be between A-A or C-C subunits.
3. Cartwheel Structure –
It is found at the proximal end of centrioles and the basal bodies. It consists of a central rod or hub in the centre and 9 spokes radiating from it. Each spoke is connected to sub-fibre-A.
A thickening X is seen near the outer end of each spoke. Another thickening Y is present in between the two X thickenings. It is connected with the X thickenings on either side and with the triplet on the outer side.
Associated Structures (Pericentriolar structures) –
Satellites –
Each centriole is surrounded by two crowns. Each crown consists of 9 amorphous plaques or spheres. These are rounded bodies attached to the centriole by short bridges of dense material. These bodies are called corpuscles or massules or pericentriolar satellites. The shape, size, and position of satellites change during spermiogenesis.
Biochemical Composition –
Centrioles are formed of structural proteins, tubulin, lipids ATPase, and RNA.
What Is The Function of Centrioles?
- Centrioles play an important role in the formation of spindles and therefore, in cell division.
- They form basal bodies of cilia and flagella.
- Distal centriole present in the spermatid forms the axial filament of the flagellum of the spermatozoon.
Centrioles vs Centrosome –
Centrosome also called Microcentrum, is the clear zone of cytoplasm surrounding the centriole. A centriole also called a cell centre is a cylindrical body formed of 9 microtubules or fibres that are arranged equidistantly in a circle around an imaginary axis. These help in spindle formation during cell division and form basal bodies of cilia and flagella.
Centrosome vs Centromere –
The centromere is the region of the chromosome where sister chromatids remain attached. The chromosome gets attached to the equator of the spindle through the centromere.
Conclusion –
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