Physics of phase separation inside biological cells - David Zwicker (Max Planck Institute of Biophysics)

Abstract:

Phase separation is crucial for partitioning the complex interior of biological cells. Phase separation leads to various droplets, known as biomolecular condensates, whose compositions are mainly controlled by genetically encoded interactions. These droplets need to form at the right time, at the right position, and with the right size to fulfill countless cellular functions. In my talk, I will discuss two physical mechanisms that enable such control. I will start with chemical reactions driven out of equilibrium, e.g., by consuming ATP. Based on thermodynamic constraints, I will show that enzymes concentrated inside or outside the droplet can create compositional gradients that affect droplet nucleation, shape, and position. In the second part of the talk, I will discuss phase separation in elastic gels, where recent experiments demonstrated the emergence of regular mesoscopic patterns. I will show that local elasticity theories cannot explain the data, even if they allow large deformations. Instead, we propose a nonlocal elasticity theory, which allows us to identify a characteristic length scale controlling the periodic patterns of droplets. Taken together, I will demonstrate that studying phase separation in cells results in unique challenges because of the complex, active environment. While cells learned to exploit the respective physics over millennia to control their droplets, we are only starting to scratch the surface of this exciting interdisciplinary field.