Figure 24.

(a) Kinesin motor proteins have two heads that bind to a microtubule repeatedly as the kinesin walks down the microtubule. Different walking mechanisms are possible, resulting in either all 8 nm steps or alternating 7 and 9 nm steps as shown. (b,c) Measuring a large number of individual steps using an optical force clamp makes it possible to distinguish that kinesin takes all 8 nm steps rather than alternating 7 and 9 nm steps. Adapted from refs (281) and (285).