Microtubules are intracellular structures that are required for cell division, organisation and intracellular transportation. In some specialised cells they are even involved in cell movement using flagella (tails) and cilia (hairs).
Microtubule nucleation is the initiation of microtubule polymerisation. It requires the formation of the gamma-tubulin ring complex from gamma-tubulin and other associated proteins. This acts as a scaffold from which tubulin dimers can begin polymerisation, and caps the (-) end to prevent depolymerisation as the (+) end continues to grow. The ring complex is the core unit of the microtubule organising centre that is essential for cell division.