Kinesin Molecular Motor Walk

Motor Conditions

ATP concentration 2.0 mM

Opposing load force 0.0 pN

Thermal noise (bath temp) 310 K

Motor State

Head: TRAILING → LEADING
Cycle: ATP binding

Steps taken

Distance walked

0 nm

Mean velocity

0 nm/s

Stall probability

How it works

Kinesin-1 is a two-headed nanoscale motor protein that walks toward the microtubule's plus end by converting the chemical energy of ATP hydrolysis into mechanical work, one 8 nm tubulin-dimer step at a time — hand-over-hand, like walking.

Chemical cycle (per head, per step):
  1. ADP-head binds ATP     (rate ∝ [ATP])
  2. ATP hydrolysis: ATP → ADP + Pi
  3. Pi release → neck-linker "power stroke"
  4. Trailing head swings 16 nm forward, binds next site (net +8 nm)

Stepping is a biased random walk. Each attempt succeeds with
probability set by the load-dependent free energy:

  P(forward) = 1 / (1 + exp[(F·d − ΔG_ATP) / (k_B T)])

  F     = opposing load force (pN)
  d     = 8 nm step size
  ΔG_ATP≈ 20 pN·nm available per hydrolysis event
  k_B T ≈ 4.1 pN·nm at 310 K (thermal energy scale)

ATP concentration — sets the ATP-binding rate that gates each step; near-zero ATP starves the motor and it stalls.
Load force — an opposing force (as from a cargo vesicle or optical trap) that raises the energy barrier per step; kinesin stalls near F ≈ 7 pN, matching single-molecule optical-trap measurements.
Thermal noise — the Brownian jitter (k_BT) that both powers the diffusive search for the next binding site and occasionally knocks a head backward.

Real-world relevance: kinesin motors haul vesicles, mitochondria and mRNA along microtubule "highways" inside every eukaryotic cell — the same mechanochemical coupling principle used to engineer synthetic DNA-origami walkers and nanoscale cargo-transport devices in nanobiotechnology.

Leading head (bound) Trailing head (stepping) Cargo / neck linker

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