A motor protein, structurally similar to myosin, that transports cargoes inside cells by interacting with microtubules. The kinesin molecule consists of two heavy chains and two light chains: the heavy chains form a pair of globular ‘heads’ and a coiled helical tail, to which the light chains attach. The heads bind alternately to a microtubule, effectively ‘walking’ along the microtubule using energy supplied by the hydrolysis of ATP. The tail region binds to a cargo, such as a vesicle or organelle, which is thereby carried along. Kinesins transport synaptic vesicles inside neurons, from the cell body along the axon to synapses; they are also involved in the assembly of the mitotic spindle and segregation of chromosomes during nuclear division.