Molecular motors are nano-tractors for all kinds of cargo within the cells of living beings. They move in a stepwise manner along filaments of the cytoskeleton, consuming energy provided by the hydrolysis of ATP, which can be considered the fuel of the cell. Kinesin and dynein motors move along microtubules and myosins move along actin filaments. The step sizes of these motors are of the order of 10 nm. By stepping in a directed fash-ion along filaments, the motors pull cargo particles which are much larger than the mo-tors themselves. In addition to their importance for the functioning of cells, molecular motors have many possible applications as biomimetic transport systems and are likely to become a key component in the emerging bio-nanotechnology.
Active transport driven by molecular motors is particularly important for nerve cells, or neurons. These cells have extended compartments, axons, which connect the cell body with the synapse, where the nerve signals are transmitted from one neuron to another. The length of axons is in the centimeter or even meter range; examples of relatively long axons are those that connect our spinal cord with the tips of our fingers and toes. Within such an axon, microtubules provide the tracks along which molecular motors transport their cargo, such as vesicles filled with neurotransmitters.