#phase separation

Inside Droplets

Phase separation – two distinct phases separating from a mixture, as vinegar and oil will from an undisturbed salad dressing – into droplets plays a role in the biochemical dynamics and signals within cells. This study uses computer modelling to understand the interaction of networks of the cell's structural protein actin with droplets of the actin binding protein VASP influences cytoskeletal architecture

Read the published research article here

Image from work by Aravind Chandrasekaran and colleagues

Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, CA, USA

Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)

Published in Nature Communications, April 2024

Living cell membranes can self-sort their components by 'demixing'

Cells—the building blocks of our bodies—are encapsulated by membranes. The same goes for the specialized compartments within our cells.

These membranes are extremely thin, oily films, containing proteins and fatty molecules called lipids. For decades, scientists have argued about how cell membranes organize and maintain distinct regions enriched in particular protein and lipid types. These regions are thought to influence cellular activities, such as the signaling that controls both normal cellular growth and the growth of cancerous cells.

In a paper published Dec. 5 in the Biophysical Journal, scientists at the University of Washington show for the first time that the complex distribution of molecules within a membrane of a living yeast cell arises through demixing. Also known as phase separation, demixing is a simple physical process that is similar to the action that causes droplets of oil to separate from vinegar in a salad dressing.

"Cells have a toolbox with a variety of resources to help them complete a variety of tasks," said senior author Sarah Keller, a UW professor of chemistry. "By teaming up with Alex Merz, a UW professor of biochemistry and a yeast expert, we've shown that phase separation is one of those tools to shape membranes and their functions within a living system."

More information: Scott P. Rayermann et al, Hallmarks of Reversible Separation of Living, Unperturbed Cell Membranes into Two Liquid Phases, Biophysical Journal (2017). DOI: 10.1016/j.bpj.2017.09.029

Phase separation in a synthetic membrane. Credit: Caitlin Cornell/University of Washington

Cheese fondue is a complex -- and delicious -- Swiss delicacy. The perfect fondue requires the right mix of ingredients and preparation to get the rheology -- the flow character -- just right. Fondue is a colloid, a fluid containing a mixture of suspended insoluble particles. 

The major components, rheologically speaking, are fat globules and casein proteins from the cheese, ethanol from the wine, and some added starch. Left on their own, the fat and casein tend to separate, something that’s sure to ruin the fondue. Adding the right amount of starch prevents that separation and keeps the fondue together. The viscosity of fondue is very important as well. If it’s too runny or too gummy, the mouthfeel will be wrong and it may not stick to the bread when dipped. Adding wine decreases the viscosity.