Biological complexity: intracellular organization (Introduction)

by David Turell , Monday, February 08, 2021, 16:29 (1172 days ago) @ David Turell

Cell proteins form membraneless droplets:

https://phys.org/news/2021-02-membraneless-organelles.html

"In cells, numerous important biochemical functions take place within spherical chambers made from proteins and RNA.

"These compartments are akin to specialized rooms inside a house, but their architecture is radically different: They don't have walls. Instead, they take the form of liquid droplets that don't have a membrane, forming spontaneously, similar to oil droplets in water. Sometimes, the droplets are found alone. Other times, one droplet can be found nested inside of another. And these varying assemblies can regulate the functions the droplets perform.

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"The research lays out physical rules controlling the arrangement of various types of synthetic MLOs created using just three kinds of building materials: RNA and two different proteins, a prion-like polypeptide (PLP) and an arginine-rich polypeptide (RRP).

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"'Different condensates can coexist inside the cells," says first author Taranpreet Kaur, a Ph.D. student in physics in the UB College of Arts and Sciences. "They can be detached, attached to another condensate, or completely embedded within one another. So how is the cell controlling this? We found two different mechanisms that allowed us to control the architecture of synthetic membraneless organelles formed inside a test tube. First, the amount of RNA in the mixture helps to regulate the morphology of the organelles. The other factor is the amino acid sequence of the proteins involved."

"'These two factors impact how sticky the surfaces of the condensates are, changing how they interact with other droplets," says Priya Banerjee, Ph.D., UB assistant professor of physics, and one of two senior authors of the paper. "In all, we have shown using a simple system of three components that we can create different kinds of organelles and control their arrangement in a predictive manner. We suspect that such mechanisms may be employed by cells to arrange different MLOs for optimizing their functional output.'"

Comment: We've seen that phase transitions are one physico-electrochemical method, stickiness is now another to corral free-floating molecules into usable networks. Still not hard-wire control which allows for errors, but obviously the required mechanism.