Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

by Brian Greene

In centuries past, such wind-powered turning motion was used to crush wheat or other grains into flour. The cellular windmills undertake an analogous grinding project but instead of pulverizing structure the process builds it. As they turn, the molecular turbines repeatedly cram together two particular input molecules (ADP, adenosine diphosphate plus a phosphate group), synthesizing one particular output molecule (ATP, adenosine triphosphate). Forced together by the turbine, the constituents of each resulting ATP molecule are in a tense arrangement: mutually repelling charged constituents are clasped together by chemical bonds, and so, much like a compressed spring, they strain to be released. That’s extraordinarily useful. Molecules of ATP can travel throughout a cell, releasing that stored energy when needed by snapping the chemical bonds and allowing the constituent particles to relax into a lower energy, more comfortable state. It is that very energy, released by the dissociation of ATP molecules, that powers cellular functions.