Insights into the relation between noise and biological complexity

TL;DR

This paper investigates how the topology and fluxes in chemical reaction networks influence intrinsic noise levels, revealing a direct relationship between network structure, complexity, and fluctuations in biological systems.

Contribution

It provides a novel analysis linking network topology and flux directions to noise modulation, advancing understanding of biological complexity and stochasticity.

Findings

Sum of Fano factors equals network rank for zero deficiency systems

Fluctuation levels increase or decrease based on flux directions and stoichiometry

Noise is reduced when fluxes target higher complexity species

Abstract

Understanding under which conditions the increase of systems complexity is evolutionary advantageous, and how this trend is related to the modulation of the intrinsic noise, are fascinating issues of utmost importance for synthetic and systems biology. To get insights into these matters, we analyzed chemical reaction networks with different topologies and degrees of complexity, interacting or not with the environment. We showed that the global level of fluctuations at the steady state, as measured by the sum of the Fano factors of the number of molecules of all species, is directly related to the topology of the network. For systems with zero deficiency, this sum is constant and equal to the rank of the network. For higher deficiencies, we observed an increase or decrease of the fluctuation levels according to the values of the reaction fluxes that link internal species, multiplied by the associated stoichiometry. We showed that the noise is reduced when the fluxes all flow towards the species of higher complexity, whereas it is amplified when the fluxes are directed towards lower complexity species.