&Bullet; physics 14, p74
The number of different types of droplets in a cell depends on the molecular components of the cell and how many types of molecules end up in a droplet.
In cells, proteins and nucleic acids can spontaneously organize themselves into “droplets” that look and behave like the known liquid ones. These droplets, each with their own specific blend of molecular ingredients, appear to be involved in a variety of biological functions. William Jacobs from Princeton University has now derived how the maximum number of droplet types depends on the number of molecular components a cell contains  . The result indicates the complex armada of droplet types that a cell can arrange in response to external stimuli.
While the initial steps of droplet formation in cells are unknown, it is believed that it occurs through a process of nucleation and growth. Each droplet contains a large number of a few specific molecules, and different types of droplets have different concentrations of these molecules.
Using a mathematical model in which molecules interact through pair-wise interactions, Jacobs shows that the maximum number of types of droplets that can form in a cell depends on how many different types of molecules are available and how many of these types end up in each droplet. In addition, the number of individual droplets grows faster than linearly with the number of molecule types.
These predictions apply to any system in which pair-wise interactions between the units can be programmed, either synthetically or through evolution, says Jacobs. This model can therefore help researchers both to understand how cells use droplet production machines and to optimally develop artificial biomimetic systems with a limited number of components.
Today, physics published another cell story that highlights how molecular structures called chromatin can play a role in the formation of droplets that form and grow in cell nuclei (Synopsis: Chromatin May Control How Droplets Form and Grow in Cells).
Christopher Crockett is a freelance writer based in Arlington, Virginia.
- WM Jacobs, “Self-organization of biomolecular condensates with common components”, Phys. Rev. Lett.126, 258101 (2021).