Past Event: Oden Institute Seminar

How molecular machines break the symmetry between forward and backward motion

Dmitrii Makarov, Professor, Department of Chemistry, and Core Faculty, Oden Institute, UT Austin

Abstract

According to Purcell’s “scallop theorem”, a bacterium cannot swim the way a much larger organism – scallop – does, i.e. via reciprocal or time-reversible periodic motion. The mechanical motion of scallops, bacteria or humans is ultimately generated by nanometer-sized molecular machines, whose action, in contrast to the more familiar macroscopic engines, relies on the randomness of thermal motion and on microscopic reversibility. For example, a car’s internal combustion engine cannot consume its exhaust products and propel the car backwards while synthesizing fresh gasoline and depositing it into its gas tank. Yet some of the molecular machines in living organisms have the ability to operate in the backward direction and to synthesize their “fuel” molecules when doing so. In this talk I will discuss whether the forward step of a molecular machine is the time reverse of its backward step. To answer this question, I will introduce two simple models for the action of such a machine: one is based on the Einstein-Smoluchowski theory of Brownian motion and the other views a machine’s dynamics as a continuous-time random walk on a network. I will show that forward/backward symmetry violation for any collective variable describing the motor dynamics occurs only if two conditions are met simultaneously: (1) the dynamics of this variable is non-Markovian and (2) the system is not in equilibrium. This talk is meant to be a pedagogical introduction into the subject, and use of any biological lingo will be expressly avoided. BIO Dmitrii E Makarov is a Professor of Chemistry and core faculty at the Oden Institute, UT Austin. His research is in the field of computational and theoretical chemical physics, with current focus on molecular biophysics, mechanochemistry, and single-molecule phenomena. **Note: Please join this Zoom seminar online with the "Audio Only" function (no video)**