Friday, September 24, 2010

Cilia and Flagella (Short Note)

Cilia and flagella are elongated appendages on the surface of some cells by which the cells including many unicellular organisms move. In non motile cells, if cilia and flagella are present they move material over the cell’s surface. Flagella are 5 to 20 times as long as cilia and move some what differently. Cilia and flagella have similar structure and consist of membrane bound cylinders that enclose the matrix. In matrix is an axonene or axial filament which consists of nine pairs of microtubules arranged in circle around two central tubules. This is called 9+2 pattern of microtubules. Each microtubule pair, a doublet also has pairs of dynein arms made up of proteins, projecting toward neighbouring doublet and spokes extending toward the central pair of microtubules. Cilia and flagella move as a result of microtubule doublets shading along one another.
In the cytoplasm at the base of each cilium or flagellum lies a short of cylindrical basal body which is also made up of microtubules and is structurally identical to the centriole. The basal body controls the growth of microtubules in cilia and flagella. Microtubules in the basal body form 9+0 pattern: nine sets of three with none in the middle.
Flagella ad cilia have fundamental similarity of ultra structure. They are made up of two central fibres surrounded by nine double peripheral fibres arranged in a circle. This bundle of fibres is called axonene. Each peripheral fibre is composed of protein tubulin and consists of A and B microtubule. Each a microtubule has pairs of arms at regular intervals along its length. Arms are composed of another protein dynein that is capable of hydrolysing ATP because it is an enzyme ATP ASE. The central fibres are connected to a microtubule of peripheral fibres by radical spokes. These fibres arise from basal granule or kinetosome that is identical in structure to axonene but has 9+0 structure and is derived from a centriole.

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