Notice Board

The Alberta RNA Research and Training Institute presents Dr. Ramon Grima from the University of Edinburgh, Scotland. His talk is titled "Mean field theory of diffusion in heterogeneous intracellular crowded conditions." The ARRTI Speaker Series is open to the public and was established to bring leading researchers to the University of Lethbridge for lectures on a broad range of topics relating to RNA research. All are welcome!

Abstract:

It is now well established that cell interiors are significantly crowded by macromolecules, which impede diffusion and enhance binding rates. However, it is not fully appreciated that levels of crowding are heterogeneous, and can vary substantially between subcellular regions. Starting from a stochastic microscopic model, we derive coupled nonlinear PDEs for the concentrations of two populations of large and small spherical particles with steric volume exclusion. By performing a perturbative expansion in the ratio of the particle sizes, we find that the diffusion of a small particle in the presence of large particles obeys an advection-diffusion equation, with a reduced diffusion coefficient and a velocity directed towards less crowded regions. The interplay between advection and diffusion leads to behaviour that differs significantly from Brownian diffusion. We show that biologically plausible distributions of macromolecules can lead to (i) highly non-Gaussian probability densities for the small particle position, including asymmetrical and multimodal densities, (ii) both sub- and super-diffusion for short times. We confirm all our results using hard-sphere Brownian dynamics simulations.