Making Molecules into Motors; July 2001; Scientific American Magazine; by R. Dean Astumian; 9 Page(s)
HUDDLED IN THE RUINS OF a house in southwestern London, the protagonist of The War of the Worlds marveled at the strangeness of Martian technology: Of their appliances, perhaps nothing is more wonderful to a man than the curious fact that what is the dominant feature of almost all human devices in mechanism is absent-the wheel is absent. An advanced technology can do away with things we regard as absolutely essential. Just that is happening now in a blossoming field at the intersection of physics, chemistry and biology: the study and construction of devices that serve as motors and pumps on the molecular scale. These mechanisms generally lack rotors, armatures and all the other trappings of conventional engines, but that is the least of their oddities. In an ordinary motor, energy is used to cause motion. In these motors, energy is used to cause a cessation of motion. Although they seem rather like an example of alien technology, they are the most common type of motor on our planet, the basis of the inner workings of all living cells.
Our physical intuition, formed by everyday observation of large machines, fails when we consider the world of the small. It is a capricious world, ruled by thermal and quantum fluctuations. For molecules, moving deterministically is like trying to walk in a hurricane: the forces propelling a particle along the desired path are puny in comparison to the random forces exerted by the environment. Yet cells thrive. They ferry materials, they pump ions, they build proteins, they move from here to there. They make order out of anarchy.