Figure 1.

Microtubule (MT) basics. MTs are linear structures comprised of α-tubulin and β-tubulin heterodimers. MTs are extremely dynamic, existing in either a growing state (polymerization) or shrinking state (depolymerization), and can rapidly switch from growth to shrinkage (catastrophe) or from shrinkage to growth (rescue). Addition of new GTP-bound heterodimers occurs at the MT plus end during polymerization. Shortly thereafter, the tubulin subunits hydrolyze their bound GTP to GDP. When the addition of GTP-bound heterodimers slows and the MT lattice is composed of predominantly GDP-tubulin, the protofilaments splay apart and the MT depolymerizes.