Think back to that basic biology class you took in high school. You probably learned about organelles, those little “organs” inside cells that form compartments with individual functions. For example, mitochondria produce energy, lysosomes recycle waste and the nucleus stores DNA. Although each organelle has a different function, they are similar in that every one is wrapped up in a membrane.
Membrane-bound organelles were the textbook standard of how scientists thought cells were organized until they realized in the mid-2000s that some organelles don’t need to be wrapped in a membrane. Since then, researchers have discovered many additional membraneless organelles that have significantly changed how biologists think about the chemistry and origins of life.
I was introduced to membraneless organelles, formally called biomolecular condensates, a couple years ago when students in my lab observed some unusual blobs in a cell nucleus. Unbeknownst to me, we had actually been studying biomolecular condensates for years. What I finally saw in those blobs opened my eyes to a whole new world of cell biology.
Like a lava lamp
To get a sense of what a biomolecular condensate looks like, imagine a lava lamp as the blobs of wax inside fuse together, break apart and fuse again. Condensates form in much the same way, though they are not made of wax. Instead, a cluster of proteins and genetic material, specifically RNA molecules, in a cell condenses into gel-like droplets.
Some proteins and RNAs do this because they preferentially interact with each other instead of their surrounding environment, very much like how wax blobs in a lava lamp mix with each other but not the surrounding liquid. These condensates create a new microenvironment that attracts additional proteins and RNA molecules, thus forming a unique biochemical compartment within cells.
Biomolecular condensates behave like liquids.
As of 2022, researchers have found about 30 kinds of these membraneless biomolecular condensates. In comparison, there are around a dozen known traditional membrane-bound organelles.
Although easy to identify once you know what you are looking for, it’s difficult to figure out what biomolecular condensates exactly do. Some have well-defined roles, such as forming reproductive cells, stress granules and protein-making ribosomes. However, many others don’t have clear functions.
Nonmembrane-bound organelles could have more numerous and diverse functions than their membrane-bound counterparts. Learning about these unknown functions is affecting scientists’ fundamental understanding of how cells work.
Protein structure and function
Biomolecular condensates are breaking some long-held beliefs about protein chemistry.
Ever since scientists first got a good look at the structure of the protein myoglobin in the 1950s, it was clear that its structure is important for its…
