In animal cells, the small organelles near the nucleus that contain microtubules and form spindle fibers during cell division are called centrioles. The junction of two centrioles located side by side is called a centrosome. In 1887 scientist Von Benden discovered it. Named after scientist Theodor Bovery in 1888.
Centrioles are present in animal cells. Most plant cells do not have it. Algae, fungi, bryophyta, pteridophyta, gymnosperms etc. plants have centrioles. Each cell has only one centriole. It is absent in protozoa, diatoms, yeasts, plant and mammalian red blood cells.
Centrioles are cylindrical and small organelles. It looks like a cylindrical barrel with two openings. It is 0.3-0.5 µm in length and about 0.15-0.25 µm in diameter. Each centriole consists of three main parts. These are-
- Cylinder wall: At the center of the centriole there is a structure like a bullock cart wheel. It is called cart wheel model. The center of the cart wheel model is called the hub. The central rod is surrounded by walls or cylinder walls. Its wall is made up of 9 bundles or microtubules. Surrounding the centriole are 9 pericentriolar satellites above and below the microtubule.
- Triplets: The centriole consists of 9 clusters of triplet molecules or triplets surrounding a cavity. Each tertiary microtubule has three equidistant subtubules. That is, each centriole (3×9) has 27 subtubules. Microtubules are attached to a central axis like the spokes of a wheel. Scientist Threadgold (1968) identified three subducts internally as A, B and C. The diameter of each subchannel is 250Å.
- Linker: Linker is a type of protein fiber. The dense protein fibers that connect the tertiary tubules are called linkers. Channel A is connected to channel B and channel B is connected to channel C by connectors.
Centrioles are arranged in pairs. Each pair of centrioles is called diplosomes. The dark fluid surrounding the centriole is called the centrosphere.
Chemical structure of centriole
The main chemical component of centriole is protein. Also contains lipids and ATP.
Function of Cetriole
- Cell Division: Centriole helps in cell division. It plays a special role in cell division.
- Mucous fibers production: During cell division, it produces mucous fibers. In the prometaphase state, the nucleus is formed. It acts as a carrier of chromosomes.
- Aster-rays: It produces aster-rays during cell division. Aster rays are formed during prometaphase in animal cells.
- Polar movement of chromosomes: It helps in the marginal movement of chromosomes. During anaphase, the cytoplasm contracts and the chromosomes move towards the poles.
- Formation of microtubules: It produces microtubules. Microtubules form the cytoskeleton.
- Sperm formation: It forms the tail of the sperm. As a result spermatozoa become motile.
- Formation of flagella: Cilia and flagella form the basal body.