Centrioles and Basal Bodies : Centrioles are cylindrical structures. They appear as small granules associated with a meiotic spindle during cell division. They occur in all lower plants, protozoa and higher animals.
Ultrastructure:
(i) Under the electron microscope, each centriole is seen to be formed of nine sets of evenly spaced peripheral fibrils of tubulin protein.
(ii) Each of these sets is a triplet composed of three microtubules. Each microtubule has a diameter of about 250 Å. The triplets are found in the matrix.
(iii) Sometimes delicate strands appear to connect sets of the triplets to each other. Also, from the central core of the cylinder, delicate strands connect sets of the triplets to each other giving a cartwheel appearance.
(iv) Basal bodies are structures similar to the centrioles. They produce cilia and flagella.
Functions of Centrioles:
(i) Centrioles are the self-duplicating bodies. They contain DNA and RNA.
(ii) The centrioles which give rise to cilia and flagella are known as basal bodies.
(iii) Out of the two centrioles in the sperm, the distal centriole forms the axial filament.
Fig.(A) T.S of Centriole, (B) Three sub-tubules,(C) A sub-tubule
Functions of Basal bodies:
(i) Cilia and flagella arise from the basal bodies.
(ii) Basal bodies are converted into centrioles.
