Thermodynamic uncertainty relation to assess biological processes

TL;DR

This paper reviews how biological processes operate near the thermodynamic uncertainty relation bound, using the uncertainty product $ ext{Q}$ to evaluate their efficiency, precision, and trade-offs in nonequilibrium states.

Contribution

It introduces the use of the thermodynamic uncertainty relation's uncertainty product $ ext{Q}$ as a quantitative measure to assess the optimality of biological processes.

Findings

$ ext{Q}$ is suboptimal at substrate concentration $[S] = K_M$.

Molecular motors and biomass production are close to the TUR bound.

Trade-offs between accuracy, efficiency, and thermodynamic cost are evident in biological systems.

Abstract

We review the trade-offs between speed, fluctuations, and thermodynamic cost involved with biological processes in nonequilibrium states, and discuss how optimal these processes are in light of the universal bound set by the thermodynamic uncertainty relation (TUR). The values of the uncertainty product $\mathcal{Q}$ of TUR, which can be used as a measure of the precision of enzymatic processes realized for a given thermodynamic cost, are suboptimal when the substrate concentration $[S]$ is at the Michaelis constant ($K_\text{M}$), and some of the key biological processes are found to work around this condition. We illustrate the utility of $\mathcal{Q}$ in assessing how close the molecular motors and biomass producing machineries are to the TUR bound, and for the cases of biomass production (or biological copying processes) we discuss how their optimality quantified in terms of $\mathcal{Q}$ is balanced with the error rate in the information transfer process. We also touch upon the trade-offs in other error-minimizing processes in biology, such as gene regulation and chaperone-assisted protein folding. A spectrum of $\mathcal{Q}$ recapitulating the biological processes surveyed here provides glimpses into how biological systems are evolved to optimize and balance the conflicting functional requirements.