Scientists at Dresden University of Technology have conducted experiments on human cells indicating that existing thermodynamic laws may not fully capture the disequilibrium in living systems. Their findings point toward the need for a new law tailored to biological processes. The study highlights differences between living and non-living systems through membrane fluctuation analysis.
The laws of thermodynamics provide tools to measure how far systems deviate from equilibrium, but they fall short for the intricate dynamics of living cells, according to a recent study. Researchers N Narinder and Elisabeth Fischer-Friedrich at Dresden University of Technology in Germany explored this gap using HeLa cells, a line of cancer cells derived without consent from Henrietta Lacks in the 1950s.
In their experiments, the team halted cell division midway with chemicals and used an atomic force microscope to probe the cells' outer membranes. This allowed precise measurement of fluctuations in the membrane—how much the microscope tip moved—and how these changed when processes like molecule morphing or protein movement were disrupted. The results showed that a standard thermodynamic approach, including the concept of 'effective temperature,' did not accurately describe these behaviors in living cells, unlike in non-living systems.
Instead, the researchers identified 'time reversal asymmetry' as a more effective measure of disequilibrium. This property assesses how much a biological process, such as molecules repeatedly connecting and splitting, would differ if reversed in time. 'The presence of time reversal asymmetry might be directly related to the fact that biological processes serve a purpose such as survival and proliferation,' says Fischer-Friedrich.
Experts welcomed the work. 'We know in biology that there’s a lot of processes that really rely on a system being out of equilibrium, but it is actually important to know how far a system is out of equilibrium,' says Chase Broedersz at Vrije Universiteit Amsterdam in the Netherlands. Yair Shokef at Tel Aviv University in Israel called it an important step for understanding active biological systems, noting the novelty of measuring multiple non-equilibrium indicators simultaneously.
Fischer-Friedrich's team aims to derive a fourth law of thermodynamics applicable only to living matter, which features internal 'set points' like biological thermostats. They are now seeking physiological observables in cells to support this development. The study appears in Physical Review X.