If you’ve ever sat through a high school biology class, you’ve likely learned about the essential organelles that make up a cell—structures like the mitochondria, which produce energy, or the nucleus, which houses DNA. Traditionally, these organelles were understood to be membrane-bound compartments that each performed specific functions. However, this long-standing view of cell organization has been upended by an exciting new discovery: membraneless organelles, or biomolecular condensates.
For years, scientists believed that all cellular structures needed membranes to define their functions and keep everything in order. But in the mid-2000s, this theory was challenged when researchers began discovering that some organelles don’t require membranes to operate. These membraneless organelles, made up of proteins and RNA molecules, can form gel-like droplets inside cells that function as distinct biochemical compartments.
To understand what a biomolecular condensate looks like, imagine the blobs of wax inside a lava lamp. As the blobs heat up, they fuse together, break apart, and form new clusters. Biomolecular condensates behave in much the same way, but instead of wax, they are composed of proteins and RNA that clump together to form droplets within cells.
Some proteins and RNAs form these condensates because they preferentially interact with each other, much like how the wax in a lava lamp sticks together but not to the surrounding liquid. This creates a localized microenvironment where additional molecules are attracted, leading to the formation of unique cellular compartments that don’t require traditional membranes. As of 2022, researchers have identified around 30 types of these condensates, compared to only a dozen membrane-bound organelles.
While some biomolecular condensates, like ribosomes and stress granules, have well-defined roles in cells, many remain a mystery. Their functions are not always clear, but scientists are beginning to realize that these membraneless structures might serve more diverse and numerous roles than previously thought. Their discovery is shaking up our understanding of cellular chemistry and the fundamental processes that govern life.
One of the most fascinating aspects of these condensates is how they challenge traditional ideas about protein structure and function. For decades, scientists have believed that a protein’s shape is crucial to its ability to perform its job. This principle has been foundational in biochemistry, particularly since the structure of the protein myoglobin was first understood in the 1950s. However, biomolecular condensates seem to break this rule. Many of the proteins involved in condensates are intrinsically disordered—meaning they lack a fixed shape but still carry out important functions.
Interestingly, researchers have also discovered that prokaryotic cells (bacteria, for example), which were previously thought to lack organelles, also contain biomolecular condensates. This finding is reshaping our understanding of bacteria, which are far more complex than previously recognized. Although only about 6% of bacterial proteins contain disordered regions, compared to 30-40% of eukaryotic proteins, scientists have detected several types of condensates in bacterial cells that contribute to cellular processes, such as RNA synthesis and degradation.
This discovery suggests that bacterial cells—long thought to be simple structures—are actually much more sophisticated than we once imagined.
The implications of biomolecular condensates extend far beyond modern biology—they also have profound implications for how we think about the origins of life on Earth. Traditionally, scientists have assumed that early life forms must have been enclosed within membranes, as all known living organisms today are. But with the discovery that RNA molecules can spontaneously form into condensates, this idea is being reexamined.
In the RNA world hypothesis, it’s proposed that the first life forms were simply RNA molecules that could replicate themselves. But how did these molecules organize into the first living structures? Until recently, it was assumed that membranes would be necessary for this process, requiring the synthesis of lipids (the fats that form membranes). However, if RNA could spontaneously form into condensates without the need for membranes, it suggests that the first life on Earth could have originated from nonliving molecules, fundamentally changing how scientists view the origin of life.
Biomolecular condensates are not just changing our understanding of cell biology—they could also lead to breakthroughs in medicine. Researchers are already investigating how to manipulate these condensates to treat diseases such as Alzheimer’s, Huntington’s, and Lou Gehrig’s disease. By developing drugs that can promote or dissolve condensates, scientists hope to find new ways to combat these debilitating conditions.
The idea that such disordered, rule-breaking structures play a key role in cellular function is revolutionizing the way we think about proteins, diseases, and even the origins of life itself. As research into biomolecular condensates continues to unfold, it’s likely that each one will eventually be assigned a specific function—an exciting prospect for both cell biology and medicine.
For future biology students, this new chapter in cellular biology may just lead to even more advanced topics to explore. So, while today’s high school biology curriculum might already be full, you can bet that in the future, students will have even more to learn about these fascinating, membraneless structures inside cells.
By Impact Lab
