Researchers at the Max Planck Institute of Molecular Cell Biology and Genetics and the Max Planck Institute of Biochemistry have shown for the first time that simple RNA is active within membraneless microdroplets, enabling a suitable environment for the beginning of life.
How life arose from non-living chemicals more than 3.5 billion years ago on Earth is a still-unanswered question. The RNA world hypothesis assumes that RNA biomolecules were key players during this time as they carry genetic information and act as enzymes. However, one requirement for RNA activity is that there are a certain number of molecules within close enough proximity to one another. This would be possible if RNA was contained within a compartment, such as membraneless microdroplets (coacervates).
The RNA world hypothesis assumes that life originates from self-replicating RNA, a biomolecule which was present before the evolution of DNA and proteins. Once formed, some of these chains were able to function as enzymes, and were even able to evolve by making copies of themselves with slight, accidental modifications. However, researchers assume that on an early planet Earth concentrations of RNA and their building blocks may have been too dilute for a reaction to take place.
Therefore, the scattered RNA molecules needed to find a way to one another to create a reaction and start life. Suitable places for accumulating RNA could have been within compartments. Compartments can be formed with a membrane such as the cell or without a membrane where molecules can exchange readily with their environment. Membraneless compartments can be formed by phase-separation of oppositely charged molecules, a process that is similar to the separation of oil drops in water.
In their study, the researchers proved for the first time that RNA is active within such membraneless microdroplets, supporting a previous hypothesis that coacervates act as protocells and could therefore be a precursor of the cell that exists today. The ability of coacervates to accumulate RNA would have helped to overcome the dilution problem of biomolecules and offered a suitable environment for reactions with each other. Furthermore, these membraneless droplets allow free transfer of RNA between the droplets.
“One of the really exciting things is that we have shown that coacervates act as a controlled genetic transfer system, in which shorter RNA pieces can shuttle between droplets while longer pieces are trapped in the hosting microdroplet,” says Dr. Björn Drobot, the first author of this study. “In this way, these protocells (coacervates) have the ability to transfer genetic information between other protocells which would have been an important criterion for starting life.”
“It was hypothesized by a Russian scientist (Oparin) in the 1920s that coacervate droplets could have been the first compartments on earth and existed before cells with a membrane evolved,” says Dr. Dora Tang, who led the project. “They provide a way for biomolecules to concentrate create the first life on Earth. The study from my lab adds to a body of work from us and others where there is increasing evidence that coacervates are interesting systems for compartmentalization in origin of life studies as well as studies in modern biology and synthetic biology.”
The Daily Galaxy via Max Planck Society
Image credit: With thanks DasWortgewand, Pixabay
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