Cilia, Centrioles and Flagella

CILIA, CENTRIOLES AND FLAGELLA

Cilia and flagella are made from microtubules covered by plasma membrane extensions. Their goal is to move the cell or move mucus, fluid, or cells over the cell surface. Microtubules and cilia are identical but they are different only in length.

Two microtubules form a doublet in cilia and in flagella. There are microtubule associated proteins that also participate in the process of cilia and flagella movement. There is a circle of nine doublets or eighteen total strands of tubulin tubules that form the outside of a flagellum or cilium. There is a central doublet, making twenty total tubules in the cilium or flagellum.

There are dynein arms that connect some of these tubules. They have ATPase activity so that, when ATP is around, they can move from one tubulin to another so the cilium or flagellum can bend. Nexin is another protein that links these microtubules in order to allow for the movement of the cilium. Centrioles will control the direction of the flagella or cilia so they can beat in unison.