RatchetRun
A molecular motor does not walk on purpose. Myosin is jostled by heat all the time; burning ATP only makes a forward grab a little more likely than a backward one, so over a whole team of heads the muscle slides on average. Set the ATP level, predict how far a jostled motor drifts, then watch it — and see how noisy a single run really is. Everything runs locally; nothing about you is collected.
This is the tool — a free prediction game. You set only the ATP level; you never place a step. A single short run often lands nowhere near the average, because each step is random — that is the point. The model and the science are written in full in the guide below (works without JavaScript). A native version, when it ships, adds offline use; it never gates the web.
Predict the drift after the run:
Loading the game… If it does not start, the full guide below still works.
How to play. Press Start. Drag the ATP slider, then pick a drift prediction (buttons or keys 1–4), then press Enter or Run. Watch the walker jostle — some steps go backward. Press Next for another round. There is no way to lose.
Why this is a random walk, not a walk
In a muscle, a huge number of myosin heads reach toward an actin filament. Each head is jostled by heat constantly. Burning ATP does not aim a head; it just makes a forward grab-and-release a little more likely than a backward one. So each head’s motion is a biased random walk: mostly noise, tilted slightly forward. Add up a whole team of heads over many cycles and the filament slides — that is muscle contraction. No head decides where to go, and no single step is placed.
What the game does
You set one number — the ATP level — which sets how much the odds tilt forward. At 0% ATP the step is a coin flip, so the average drift is zero (but a single short run still wanders — sometimes backward!). As ATP rises, forward becomes more likely, so the average drift grows. You predict the drift, then watch one run. The gap between “what usually happens” and “what this one run did” is the lesson: direction is a statistical bias, not a plan.
Methods & about
This is a teaching model, honest about being a simplification. Muscle myosin (myosin II) is not a processive walker — a single head is attached only a small fraction of the time; real sliding is produced by a team of low-duty-ratio heads working as a ratchet, which is why this game scores the ensemble average, not one head. (The classic hand-over-hand “walking” motor is myosin V.) The simulation is a transparent biased random walk: each jostle steps forward with probability 0.5 + 0.3 × (ATP ÷ 100), else backward, for 40 jostles. The structure is the real AlphaFold prediction of human MYH7 (P12883), shown for illustration. The game keeps no score history, uses no accounts, and sends nothing anywhere.
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