How kinesin walks: rectifying thermal noise with asymmetric potentials
Flashing Ratchet (Astumian & Hänggi 2002): A particle in an asymmetric sawtooth potential
experiences directed motion from noise alone when the potential periodically flashes on/off.
When off, particles diffuse freely. When on, the steep right wall traps those
that diffused left, while particles near the shallow slope slide right — net drift emerges.
This models kinesin's ATP-driven stepping: hydrolysis toggles a binding potential, converting
chemical energy into directed mechanical work against thermal fluctuations (~4 pN·nm per step).
Key physics: detailed balance is broken by ATP hydrolysis (nonequilibrium).
Without energy input, the second law forbids directed transport — even with asymmetry.