Centrioles are a pair of cell organelles, composed primarily of tubulin (a type of protein). They usually help during cell division.
In this article on centrioles facts, we are going to learn about their shape and their functions. Are you ready?
Of course, you are…
Centrioles Facts: 1-7 | What are they and where are they found?
1. Centrioles are two cylindrical, rod-shaped microtubular structures present near the nucleus.
2. Centrosome is an area in the cytoplasm where centrioles are formed.
3. Centrioles are present in lower plants, all groups of animals, and in primitive flagellates like Chlamydomonas, dinoflagellates etc.
4. They are completely absent in red algae, yeast, conifers (cone bearing plants), and angiosperms (flowering plants).
5. They aren’t seen in some of the non-ciliated and non-flagellated protozoans.
6. Some amoebae species have both flagellated and amoeboid stages of development.
7. In such species of amoebae, a centriole develops during the flagellated stage and disappears during amoeboid stage.
Centrioles Facts: 8-12 | Position, discovery and naming
8. The word centriole is formed by the combination of ‘centri’ and ‘ole’ which basically means little central part.
9. This cell organelle is named after its position (nearly at the center) in the cell.
10. Edouard van Beneden was the first person to make an observation of the centrioles in the year 1883.
11. In 1895, Theodor Boveri named centriole as “centrosome”.
12. Etienne de Harven and Joseph G. Gall were the first people to work out the pattern of the duplication of the centrioles. It is to be noted that they worked it out independently.
Centrioles Facts: 13-15 | Structure of centrioles
13. Centrioles and basal bodies (basal bodies are modified centrioles from which flagella and cilia arise) are cylindrical in shape.
14. They are around 0.15 to 0.25 μm in diameter and 0.3 to 0.7 μm in length. However, there are reports that centrioles and basal bodies can be as long as 8 μm or as short as 0.16 μm.
15. Centrioles and basal bodies have similar structure which are as follows:
(A) Cylinder Wall:
(i) Nine triplet microtubules are arranged around the perimeter of an unreal cylinder. The triplets form a helix structure.
(ii) The triplet microtubules are equally spaced from each other.
(iii) The space between these triplets are filled by an amorphous material which is highly electron dense.
(iv) If you cut the centriole horizontally or in transverse section, it can be seen that the triplets are arranged like blades of a turbine.
(v) Triplets form the wall of the cylinder of the centriole or basal body.
(vi) It has to be noted that there is no limiting membrane and the triplets form the wall.
(B) Triplets:
(i) The triplets are similar in both centrioles and basal bodies.
(ii) Each triplet has 3 units which are called tubules.
(iii) Each tubule is around 200 to 260 Å. The innermost tubule of the triplet is round in shape and the other two are c-shaped, incomplete and share their wall with the tubule preceding them.
(iv) The outer tubule is shorter than the other two.
(C) Linkers:
(i) Linkers are the proteins that bind these three tubules and form a triplet.
(ii) The tubules are linked all along the length.
(D) Cartwheel:
(i) Each triplet produces faint protein spokes to form a central core which looks like a cartwheel.
(ii) The cartwheel is seen at the proximal end of the centriole. The cartwheel gives centriole a structural and functional polarity.
(iii) Centriole grows from the distal end (the other end of the centriole). Procentrioles (an early developmental stage of a centriole or a basal body) are present at proximal end.
(iv) The cilia or flagella arise from the basal body where the cartwheel is present.
(E) Ciliary Rootlets:
(i) Ciliary rootlets are cytoskeleton kind of structures which arise from basal bodies.
(ii) There are two types of ciliary rootlets which are:
- Tubular root fibrils – The tubular root fibrils have around the diameter by 200 Å.
- Striated rootlets – Most of the ciliary rootlets are striated (or stripped). The striated rootlets are made up of microfilaments. It is because of the microfilaments; the ciliary rootlets can contract. The ciliary rootlets may also serve as anchor for the basal body.
(F) Basal Feet and Satellites:
(i) Basal feet are the dense processes which are arranged perpendicularly to the basal body.
(ii) Basal body has structural asymmetry because of the basal feet.
(iii) Basal feet are made up of microfilaments. Basal feet act as a point where microfilaments converge.
(iv) Satellites are also called the pericentriolar bodies.
(v) The satellites are electron-dense structures which are present near the centriole.
Centriole Facts: 16-19 | Chemical Composition of Centrioles, DNA, RNA and functions
16. The microtubules present in centrioles and basal bodies contain a protein called tubulin. Apart from the tubulin protein, lipid molecules are also present.
17. There is a controversy revolving around the centrioles about whether centrioles and basal bodies have DNA and RNA.
18. Chandler Fulton (1971) doubted the presence of DNA and RNA in basal bodies and centrioles.
19. Though centrioles are very small and they serve multiple functions which are as follows:
(i) One of the main function of centrioles is the formation of basal bodies and eventually the formation of cilia.
(ii) Both centrioles and basal bodies play a role in flagellar and ciliary beat.
(iii) Centrioles are the focal point of centrosome (another cell organelle). The centrosome organizes the microtubules and form mitotic spindle.
(iv) In Chlamydomonas the basal bodies themselves act as mitotic spindle.
(v) In sperms, one of the centrioles turns into the tail fiber of the sperm or flagellum.
(vi) Both the centrioles and basal bodies help in the reception of acoustic (sound), optical (sight) and olfactory (smell) signals.
(vii) It has been suggested by Albercht-Beuhler that centrioles can work as devices for the locating the direction of signals inside the cells. It is achieved by the geometric design of centrioles which matches with manmade devices like radar scanner.
This concludes our article on centrioles facts. If you want us to write more on similiar topics like centrioles facts, do let us know in the comment section.
Sources:
- Cell Biology by P S Verma and V K Agarwal, Chapter 28 Centrioles and Basal Bodies, from Page Number 583 – 588.