With the chaos in the average cell stemming from the constant flux in the movement of proteins and molecules, understanding and predicting how any given process might change is a difficult process. However, it is also essential in determining how well a cell is performing. Now, physicists from MIT have narrowed down one factor that can be used to predict a cell's fluctuations: energy.
The amount of energy a cell is using can be used to determine the fluctuations in particular processes and protein quantities, allowing scientists to determine the range or limits of these processes and pinpoint fluctuations that would be impossible given the laws of thermodynamics. In addition, scientists can also use the new idea to determine the minimum amount of energy needed to conduct specific cellular actions.
"This ends up being a very powerful, general statement about what is physically possible, or what is not physically possible, in a microscopic system," said Jeremy England, who headed the research. "It's also a generally applicable design constraint for the architecture of anything you want to make at the nanoscale."
England and his team took a general master equation, which describes the motion of small systems, and applied a large deviation theory, a mathematical technique used to determine the probabilities of specific processes over a long period of time. Using this equation and technique, they calculated how a microscopic system behaved over time in terms of fluctuations and calculated a probability distribution for each one.
The distribution had a general form, showing that certain molecular behaviors can be bounded by just one mathematical expression. After translating this expression into thermodynamic terms in order for it to be applied to cell fluctuations and microscopic systems, they found that energy is the variable that constrains the processes changing in these kinds of environments.
"We have in mind trying to make some sense of molecular systems," said Todd Gingrich, co-author of the study. "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."
Using their findings, the team can better understand the energy requirements in certain cellular systems and aid in the design of synthetic molecular devices.
"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 said. "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."
The findings were published in the March 21 issue of Physical Review Letters.
