MICROTUBULES
Microtubules are long thin unbranched cylinders. Their outer diameter is about 24 nm, and the inner one is 15 nm; the length is 102 to 106 nm. The main component of microtubules is the protein tubulin. Besides it, about 20 various proteins are compounds of microtubules. Microtubules play the key role in cell division, secretion, intercellular transport of substances, morphogenesis, cilia and flagella movements.