Life's Ratchet: How Molecular Machines Extract Order From Chaos

Peter Hoffman is a physicist and materials scientist, and he brings those perspectives and sensibilities to the description of how life converts chemical energy into order and motion.  The "Ratchet" in the title is Feynman's Ratchet, a gedanken experiment described in Feynman's "Lectures on Physics" and reminiscent of Maxwell's Demon.  The Demon was proposed as a way to create a temperature difference without expenditure of energy, by sorting molecules according to their speeds.  The Ratchet, by contrast, has no intelligence; it consists of a nanoscale cogged wheel that can rotate in one direction when impacted by an energetic molecule but is prevented from going in the opposite direction by a sensitive pawl.  It can be shown (as Hoffman explains) that neither of these machines can work as conceived.  However, the machines that actually do work in life are even more amazing. I have not seen a better description of how the chemical energy of ATP is converted to mechanical motion by kinesin, dynein, and myosin V, working against microtubules and actin.  Readers of the Journal should not have trouble with the biochemistry described, but it might be a bit technical for the general public.

Publication Date: 
Tuesday, April 30, 2013