The Vital Question: Why is life the way it is?

by Nick Lane

In our mitochondria, then, we have an electrical circuit, in which the membrane works as an insulator: we pump protons across the membrane, and most of them return through proteins that behave as turbines, driving work. In the case of the ATP synthase, the flow of protons through this nanoscopic rotating motor drives ATP synthesis. But note that this whole system depends on active pumping. Block the pumps and everything grinds to a halt. That’s what happens if we take a cyanide pill: it jams up the final proton pump of the respiratory chain in our mitochondria. If the respiratory pumps are impeded in this way, protons can continue to flow in through the ATP synthase for a few seconds before the proton concentration equilibrates across the membrane, and net flow ceases. It is almost as hard to define death as life, but the irrevocable collapse of membrane potential comes pretty close.