Think back to the basic biology class you took in high school. Maybe you learned about Organellesthose small “organs” found 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 each one is encased in a membrane.
Membrane-bound organelles have been the standard for how scientists think about organizing cells Until they realized it in the mid-2000s Some organelles do not need to be wrapped by a membrane. Since then, researchers have discovered many additional non-membrane organelles that have dramatically changed the way biologists think about the chemistry and origins of life.
You’ve learned about non-membrane organelles, which are formally called Biomolecular condensatestwo years ago when students In my lab Notice some unusual dots in the 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 an idea of what biomolecular condensates look like, imagine a lava lamp with the wax blobs inside merging together, breaking apart and merging again. Capacitors Formed in much the same wayAlthough it is not made of wax. Instead, a collection of proteins and genetic materials, specifically ribonucleic acid (RNA) molecules, condense in the cell into jelly-like droplets.
Some proteins and RNAs do this because they interact preferentially with each other rather than with their surrounding environment, much like how blobs of wax in a lava lamp mix with each other but not with the surrounding liquid. These condensates create a new microenvironment that attracts additional proteins and RNA molecules, thus forming a unique biochemical compartment within cells.
As of 2022, researchers have discovered approx 30 types of these non-membrane biomolecular condensates. In comparison, there are about a dozen known conventional membrane-bound organelles.
Although it’s easy to identify once you know what you’re looking for, it’s harder to know exactly what biomolecular condensates do. Some have well-defined roles, such as shaping Reproductive cells, Stress granules and Ribosomes that make protein. However, many others do not have clear functions.
Non-membrane-bound organelles can have more numerous and diverse functions than their membrane-bound counterparts. Learning about these unknown functions affects scientists’ basic understanding of how cells work.
Protein structure and function
Biomolecular condensates break down some long-standing beliefs about protein chemistry.
Since scientists first took a closer look at Structure of myoglobin protein In the 1950s, it was clear that its structure was important for its ability to transport oxygen to muscles. Since then, the mantra of biochemists has been that protein structure equals protein function. Basically, proteins have specific shapes that allow them to perform their functions.
The proteins that form biomolecular condensates break this rule at least partly because they contain disordered regions, meaning they have no defined shapes. When researchers discovered these so-called Intrinsically disordered proteins, or IDPsIn the early 1980s, they were initially puzzled by why these proteins lacked a robust structure while still performing specific functions.
Later, they found out IDPs tend to form condensates. As is often the case in science, this discovery solved one mystery about the roles these dysregulated rogue proteins play in the cell only to open another, deeper question about what biomolecular condensates really are.
Bacterial cells
As researchers discovered Biomolecular condensates in prokaryotesor bacterial cells, which have traditionally been defined as not containing organelles. This discovery could have profound implications for how scientists understand the biology of prokaryotic cells.
Just about 6% bacterial proteins They contain disordered regions that lack structure, compared to 30% to 40% of eukaryotic or non-bacterial proteins. But scientists have found many biomolecular condensates in prokaryotic cells that are involved in a variety of cellular functions. Including making and Degrading RNAs..
The presence of biomolecular condensates in bacterial cells means that these microbes are not simple bags of proteins and nucleic acids but are in fact more complex than previously recognized.
Origins of life
Biomolecular condensates are also changing the way scientists think about the origins of life on Earth.
There is ample evidence that nucleotides, the building blocks of RNA and DNA, can be made from common chemicals, such as hydrogen cyanide and water, in the presence of common energy sources, such as ultraviolet light or high temperatures, and on universally common metals, such as Silica and iron clay.
There is also evidence that single nucleotides can form spontaneously Grouping into strings To make RNA. This is a crucial step in The RNA world hypothesis.Which posits that the first “life forms” on Earth were strands of ribonucleic acid (RNAs).
A key question is how RNA molecules can develop mechanisms to replicate and organize themselves in a protocell. Since all known life forms are surrounded by membranes, researchers studying the origin of life have often assumed that membranes would also need to encapsulate this RNA. This requires the synthesis of lipids, or lipids, that make up the membranes. However, the materials needed to form fats were not present on early Earth.
With the discovery of this RNAs can spontaneously form biomolecular condensatesFat will not be needed to form progenitor cells. If RNAs are able to assemble into biomolecular condensates on their own, it becomes more plausible that living molecules arose from nonliving chemicals on Earth.
New treatments
For me and other scientists who study biomolecular condensates, it is exciting to dream about how these rule-breaking entities will change our view of how biology works. Capacitors are already there Change how we are Think about human diseases Such as Alzheimer’s disease, Huntington’s disease, and Lou Gehrig’s disease.
To this end, researchers are developing several new methods Processing condensates for medical purposes Such as new drugs that can enhance or dissolve condensates. It remains to be determined whether this new approach to treating the disease will bear fruit.
In the long term, I would not be surprised if each biomolecular condensate is eventually assigned a specific function. If this happened, you can bet that high school biology students would have more to learn — or complain about — in their introductory biology classes.
This article was republished from Conversationan independent, non-profit news organization bringing you trustworthy facts and analysis to help you understand our complex world. It was written by: Alan Albig, Boise State University
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Alan Albig receives funding from the National Institutes of Health.