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“We have in mind trying to make some sense of molecular systems,” Gingrich says. “What this proof tells us is, even without observing every single feature, by measuring the amount of energy lost from the system to the environment, it teaches us and limits the set of possibilities of what could be going on with the microscopic motions.”
Pushing out of equilibrium
The team found that the minimum amount of energy required to produce a given distribution of fluctuations is related to a state that is “near-equilibrium.” Systems that are at equilibrium are essentially at rest, with no energy coming in or out of the system. Any movement within the system is entirely due to the effect of the surrounding temperature, and therefore, fluctuations in whether a protein turns clockwise or counterclockwise, for example, are completely random, with an equal chance of rotating in either direction. Near-equilibrium systems are close to this state of rest; directional motion is generated by a small input of energy, but many features of the motion still appear as they do in equilibrium.
Most living systems, however, operate far from equilibrium, with so much energy constantly flowing into and out of a cell that the fluctuations of molecular proteins and processes do not resemble anything in equilibrium. Lacking a similarity to equilibrium, it has been hard for scientists to uncover many general features of nonequilibrium fluctuations. England and his colleagues have shown that a comparison can nevertheless be made: Fluctuations occurring far from equilibrium must be at least as large as those that occur near equilibrium.
The team says scientists can use the relationships established in its proof to understand the energy requirements in certain cellular systems, as well as to design reliable synthetic molecular machines.
“One of the things that’s confusing about life is, it happens on a microscopic scale where there are a lot of processes that look pretty random,” Gingrich says. “We view this proof as a signpost: Here is one thing that at least must be true, even in those extreme, far-from-equilibrium situations where life is operating.”
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