Liquid-liquid phase separation in living biological membranes is usually described as occurring on sub-micron length scales. A stunning counterexample occurs in S. cerevisiae. When the yeast shift from the log stage of growth to the stationary stage, huge, micron-scale liquid domains appear in the membranes of the vacuole, an endosomal organelle. These phases are functionally important, enabling yeast survival during periods of stress. We have shown that this miscibility transition is reversible as would be expected from equilibrium thermodynamics, even though it occurs in a living system. Moreover, yeast actively regulate this phase transition to hold the membrane transition ~15C above the yeast growth temperature. If time permits, this seminar will also include data on shark intestines, a biological system at a much larger length scale. Recent work proposed that helical structures inside shark intestines function as Tesla valves, favoring flow down the digestive tract. We designed and 3D printed biomimetic models of shark intestines in both rigid and deformable materials to test which physical parameters of the helices result in the largest flow asymmetries. When we printed the biomimetic models in elastomeric materials so that flow could couple to the structure’s shape, we found that flow asymmetry is magnified 7-fold.
Sarah L. Keller, the Duane and Barbara LaViolette Professor of Chemistry, is a biophysicist at the University of Washington in Seattle. She investigates self-assembly, complex fluids, and soft matter systems. Her research group’s primary focus concerns how lipid mixtures within bilayer membranes give rise to complex phase behavior. She is a Fellow of the American Physical Society and a Fellow of the Biophysical Society.