Microtubule Dynamic Instability

Individual microtubules switch stochastically between growth and catastrophe. The GTP cap model: loss of the cap triggers catastrophe; rescue re-establishes growth.

Parameters

Growth rate v_g 2.0 μm/min

Shrink rate v_s 12 μm/min

Catastrophe f_cat 0.05/s

Rescue f_res 0.03/s

Filaments 8

Growing (GTP cap)
Shrinking
MTOC (origin)

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Length over time (kymograph)

Length histogram

Dynamic instability (Mitchison & Kirschner 1984) is a remarkable non-equilibrium phenomenon: microtubules stochastically switch between persistent growth and rapid shrinkage. The GTP cap model explains this: tubulin-GTP polymerizes, then GTP hydrolyzes to GDP. As long as a cap of GTP-tubulin remains at the plus end, the filament grows. When hydrolysis catches up and the cap is lost, the lattice is destabilized (GDP-tubulin) and catastrophe begins. Rescue (GTP-tubulin islands or re-association) can restart growth. This "search and capture" strategy allows the cell to rapidly explore space and find kinetochores during mitosis.