Regensburg 2016 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 4: Colloids and Complex Fluids I (Joint Session BP/CPP/DY)

BP 4.5: Vortrag

Montag, 7. März 2016, 10:30–10:45, H45

How to regulate droplet position in a heterogeneous chemical environment? — •Samuel Krüger^{1, 2}, Christoph A. Weber¹, Jens-Uwe Sommer^{2, 3}, and Frank Jülicher¹ — ¹Max Planck Institute for the Physics of Complex Systems, Dresden — ²Leibniz Institute of Polymer Research Dresden e.V., Dresden — ³Technische Universität Dresden, Institute of Theoretical Physics, Dresden, Germany

Cells contain chemical components that are not separated from the cytoplasm by a membrane. An example are P-granules in the C. elegans embryo. They are liquid-like structures, that form droplets. They consist of RNA and proteins that are segregated spontanuously from the cytoplasm and are known to play a role in the specification of germ cells. During asymmetric cell division, P granules are segregated to one side of the cell. This segregation is guided by a spatial concentration gradient of the protein Mex-5. We simplify the multicomponent nature of the cytoplasm with a ternary model: The P granule material, the solvent (cytoplasm), and a regulator corresponding to Mex-5. Using this model we aim to understand the physical principles controlling the droplet position in a simplified scenario, where an external potential establishes the regulator gradient. We use the Flory-Huggins mean field theory and calculate the equilibrium solutions by minimizing the free energy functional. There are two equilibrium states. Droplets either localize at high external potential or low external potential. Changing the interaction between the regulator and the solvent we find that the free energy exhibits a kink indicating that the transition between both states being a discontinuous phase transition.