Fig. 1. The structure and dynamics of microtubule: Microtubules are composed of α- and β-tubulin heterodimers that polymerizes using guanosine-5′-triphosphate (GTP) to form a single proto-filament. The tubulins are arranged in a polarized manner whereby the α-tubulins are exposed at the negative (−) and the β-tubulins at the positive (+) end. The (−) end is more stable, whereas the (+) end can polymerize (grow) and depolymerize (shrink) rapidly, thus rendering microtubules highly dynamic structures. GDP: guanosine 5′-diphosphate.