Before Mitchell, everyone assumed that cells got their energy using straightforward chemistry. The universal energy currency of life is a molecule called ATP. Split it and energy is released. ATP powers most of the energy-demanding processes in cells, from building proteins to making muscles move. ATP, in turn, was thought to be generated from food by a series of standard chemical reactions. Mitchell thought otherwise. Life, he argued, is powered not by the kind of chemistry that goes on in a test tube but by a kind of electricity.More, much more, at the link about how chemiosmosis might be the key to understanding the origin of life on earth.
The energy from food, he said, is used to pump positively charged hydrogen ions, or protons, through a membrane. As protons accumulate on one side, an electrochemical gradient builds up across the membrane. Given the chance, the protons will flow back across, releasing energy that can be harnessed to assemble ATP molecules. In energy terms, the process is analogous to filling a raised tank with buckets of water, then using the water to drive a waterwheel.
Mitchell dubbed his theory chemiosmosis, and it is not surprising that biologists found it hard to accept. Why would life generate energy in such a complicated and roundabout way, when simple chemical reactions would suffice? It just didn't make sense.
Or read the snapshot version: from hydrothermal vents to full-fledged cells in ten increasingly plausible steps.