Using large "macromolecules" called polymers, researchers at Penn State University created primitive cell-like structures that they infused with RNA and demonstrated how the molecules would react chemically under conditions that might have been present on the early Earth.
Researchers led by Christine Keating and Philip Bevilacqua, probed one of the nagging mysteries of the RNA-world hypothesis.
To test how early cell-like structures could have formed and acted to compartmentalise RNA molecules even in the absence of lipid-like molecules that make up modern cellular membranes, researchers generated simple, non-living model "cells" in the laboratory.
"Our team prepared compartments using solutions of two polymers called polyethylene glycol (PEG) and dextran," Keating said.
"These solutions form distinct polymer-rich aqueous compartments, into which molecules like RNA can become locally concentrated," said Keating.
The team found that, once the RNA was packed into the dextran-rich compartments, the molecules were able to associate physically, resulting in chemical reactions.
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"Interestingly, the more densely the RNA was packed, the more quickly the reactions occurred," Bevilacqua explained.
"We noted an increase in the rate of chemical reactions of up to about 70-fold. Most importantly, we showed that for RNA to 'do something'- to react chemically - it has to be compartmentalised tightly into something like a cell," he said.
In modern biology, all life, with the exception of some viruses, uses DNA as its genetic storage mechanism.
According to the "RNA-world" hypothesis, RNA appeared on Earth first, serving as both the genetic-storage material and the functional molecules for catalysing chemical reactions, then DNA and proteins evolved much later.
"A missing piece of the RNA-world puzzle is compartmentalisation," Bevilacqua said.
"It's not enough to have the necessary molecules that make up RNA floating around; they need to be compartmentalised and they need to stay together without diffusing away.
"This packaging needs to happen in a small-enough space -- something analogous to a modern cell -- because a simple fact of chemistry is that molecules need to find each other for a chemical reaction to occur," they said.
Our experiments with aqueous two-phase systems (ATPS) have shown that some compartmentalisation mechanism may have provided catalysis in an early-Earth environment, they said.
The study findings are published in the journal 'Nature Chemistry'.