kinesins

Meaning: Kinesins are motor proteins with two globular heads that bind microtubules and a tail that binds cargo such as vesicles or organelles. ATP binding and hydrolysis make the heads alternately attach and release, so the protein walks along the microtubule. Most kinesins move toward the plus end (the β-tubulin end), which usually points toward the cell periphery. In an axon this is anterograde transport, from the cell body to the terminal. A few kinesins move toward the minus end.

On the MCAT: Passages describe axonal transport, vesicle movement, or spindle function in mitosis. Typical questions ask which motor carries cargo toward the axon terminal (kinesin) and which returns it to the cell body (dynein), or what happens when ATP is depleted or microtubules are disrupted (transport slows or stops). Kinesin's ATPase activity also ties it to questions about energy use.

Common confusion: Kinesin and dynein both travel on microtubules but in opposite directions, whereas myosin travels on actin filaments. Kinesin is the motor, not the track: the microtubule is the track, and kinesin is not a structural filament. Kinesin also does not merely bind ATP like a switch; it hydrolyzes it to drive each step.