Random walk of passive tracers among randomly moving obstacles

TL;DR

This paper investigates how the diffusion of a passive biomolecule is affected by randomly moving obstacles in a crowded environment, using CTRW to compute the diffusion coefficient and exploring implications for cellular processes.

Contribution

It introduces a model for passive tracer diffusion among moving obstacles using CTRW and analyzes how obstacle density impacts diffusion in cellular environments.

Findings

Diffusion coefficient decreases with increasing obstacle density.

Passive tracers can be significantly slowed down by moving obstacles.

Electrodynamic forces may be necessary to accelerate biomolecules in crowded environments.

Abstract

Background: This study is mainly motivated by the need of understanding how the diffusion behaviour of a biomolecule (or even of a larger object) is affected by other moving macromolecules, organelles, and so on, inside a living cell, whence the possibility of understanding whether or not a randomly walking biomolecule is also subject to a long-range force field driving it to its target. Method: By means of the Continuous Time Random Walk (CTRW) technique the topic of random walk in random environment is here considered in the case of a passively diffusing particle in a crowded environment made of randomly moving and interacting obstacles. Results: The relevant physical quantity which is worked out is the diffusion cofficient of the passive tracer which is computed as a function of the average inter-obstacles distance. Coclusions: The results reported here suggest that if a biomolecule, let us call it a test molecule, moves towards its target in the presence of other independently interacting molecules, its motion can be considerably slowed down. Hence, if such a slowing down could compromise the efficiency of the task to be performed by the test molecule, some accelerating factor would be required. Intermolecular electrodynamic forces are good candidates as accelerating factors because they can act at a long distance in a medium like the cytosol despite its ionic strength.