Tubulin is the major building block of microtubules. This intracellular cylindrical filamentous structure is present in almost all eukaryotic cells. Microtubules function as structural and mobile elements in mitosis, intracellular transport, flagellar movement, and in the cytoskeleton. Tubulin is a heterodimer, which consists of a-tubulin and b-tubulin; both subunits have a molecular weight of 55 kDa and share considerable homology. The most studied tubulins have been isolated from vertebrate brains. The microtubules can be viewed in immunofluorescent microscopy, which enables the observation of the intracellular organization of proteins that are in the form of a supramolecular structure.