(From R. Dean Astumian, “Making Molecules Into Motors”, Scientific American, July 2001, pp. 57-64.)

Or, it could be put in reverse: cell biology is nanochemistry. The mechanisms described here throw additional light on the basis and origin of life as well.

Brownian motion is a basic factor of any structure small enough to be buffetted about by collisions with small molecules. Contrary to what one might think, this “chaos” does not hinder the formation of structure or the function of these small structures (e.g. nano-motors that turn), but actually helps it along. The large scale metaphor for this is a car at the bottom of a hill being pushed uphill by hail in a hailstorm if a ratchet brake (that hinders downward but not upward motion} exists and the driver randomly releases and applies the brake. The hailstones correspond to the molecules in Brownian (random) motion; because of the ratchet, motion in one direction is favored

However, we have not created a Maxwell demon, violating the Second Law of Thermodynamics. The driver pushing the brake supplies the energy; the wonder is that, even when he does so randomly, the car still tends to move upward over time. So life, in working such mechanisms on the nano-scale, still needs free-energy gradients, as previously supposed. The mechanisms would not work in the equilibrium state, but only at states far from equilibrium.

Cellular structures that work in this way include ion pumps in cell membranes, transport of proteins in the cell along the microtubule tracts, and muscle contraction (an alternative theory to the usual one). An extension of this mechanism to an even smaller quantum level may have further applications.

Biological system ideas are now inspiring research into artificial nano structures. The chemistry of molecules can be exploited to manufacture artificial nano-motors. Are we heading for artificial life? And then what?