Society of Physics Students Talk: Simon Mochrie, Yale Physics, “Biological physics: single molecules in vitro and in vivo”

I will talk a little about what Biological Physics is. Then, I will describe two projects at the interface of physics and biology. The goal of the first project is to explore and test our current understanding of biomolecular reactions and transitions, namely that such transitions should be conceived as diffusion along a reaction coordinate. Such diffusive motions have not previously been observed directly. I will present an analysis of thousands of single-molecule transitions, observed at different forces and ionic concentrations, using an optical trap and associated data acquisition system, and resolved with microsecond time resolution. These measurements permit us to directly observe the time evolution across the transition path and the distribution of transition path times, providing compelling evidence of diffusion. The second project involves some elegant new statistical tools for analyzing diffusion of thousands of individual molecules inside living cells, and new ways of conceptualizing these data, with the eventual goal of being able to characterize processes and biochemistry, occuring inside living cells.