In biology, much of what we understand to be protein-based molecular motors may also in fact be Brownian motors. These molecular motors facilitate critical cellular processes in living organisms and, indeed, are fundamental to life itself.
Researchers have made significant advances in terms of examining these organic processes to gain insight into their inner workings. For example, molecular Brownian motors in the form of several different types of protein exist within humans. Two common biomolecular Brownian motors are ATP synthase, a rotary motor, and myosin II, a linear motor. The motor protein ATP synthase produces rotational torque that facilitates the synthesis of ATP from Adenosine diphosphate (ADP) and inorganic phosphate (P) through the following overall reaction:
ADP + P + 3H ⇌ ATP + HO + 3H
In contrast, the torque produced by myosin II is linear and is a basis for the process of muscle contraction. Similar motor proteins include kinesin and dynein, which all convert chemical energy into mechanical work by the hydrolysis of ATP. Many motor proteins within human cells act as Brownian motors by producing directed motion on the nanoscale, and some common proteins of this type are illustrated by the following computer-generated images.