The inside of every cell in our body is like a crowded city, filled with tracks, transports, libraries, factories, power plants, and garbage disposal units. The city’s workers are protein machines, which metabolize food, take out the garbage, or repair DNA. Cargo is moved from one place to another by molecular machines that have been observed walking on two legs along protein tightropes. As these machines go about their business, they are surrounded by thousands of water molecules, which randomly crash into them a trillion times a second. This is what physicists euphemistically call “thermal motion.” Violent thermal chaos would be more apt.
How any well-meaning molecular machine could do good work under such intolerable circumstances is puzzling. Part of the answer is that the protein machines of our cells, like tiny ratchets, turn the random energy they receive from water bombardment into the very directed motion that makes cells…