Physics Colloquium - Transport in Cell Biology Relies on Free Energy and Geometry

Transport in Cell Biology Relies on Free Energy and Geometry

Dr. Aidan I. Brown
Post-doctoral Fellow
University of California

Abstract:
Transport in cell biology is stochastic due to substantial fluctuations present at the nanoscale. Moving molecules and large cellular structures across the cell and within complex cellular compartments poses meaningful challenges. Transport underpins and interconnects many processes within cells, including those involved in signaling, metabolism, and protein secretion. Cellular components can move passively, through diffusion; or actively, typically driven by conversion of chemical fuel. Investigating passive and active transport modes within cells probes nanoscale physics and provides insight into strategies used by cells to obtain order. Nanoscale motors pulling (often much larger) cargo through the cell is an important and perhaps the most well-known cellular transport process. As an active process, these molecular motors consume free energy to operate --- I will explain how to use a given amount of free energy to maximize motor speed. I will also explore how free energy limits the precision of transport by molecular motors. I will then switch to diffusive transport, within the cellular geometries provided by extensive networks of tubular membrane, each enclosing a single connected volume containing many proteins passively searching for reaction partners and binding sites. Diffusive search times are largely dictated by simple geometric characteristics of these tubular networks, which connect with percolation theory to provide a bridge from messy real-world networks to a more tractable physical model. Overall, these transport processes point to how cell biology is limited and driven by fundamental physical principles.

Speaker Bio:
Aidan grew up in Ontario, Canada, completing his BSc in Physics at the University of Guelph. He worked with Andrew Rutenberg at Dalhousie University for his MSc and PhD, exploring a variety of problems in theoretical biological physics, from the scale of multicellular systems down to subcellular compartments. As a postdoctoral scholar with David Sivak, Aidan examined energy use by molecular machines, and is currently working with Elena Koslover at the University of California, San Diego, focusing on the effect of geometry on intracellular transport.