One of the major unanswered questions about the origin of life is how droplets of RNA floating around the primordial soup turned into the membrane-protected packets of life we call cells.
A new paper by researchers with the University of Chicago and the University of Houston proposes a solution.
They show how rainwater could have helped create a meshy wall around protocells 3.8 billion years ago, a critical step in the transition from tiny beads of RNA to every bacterium, plant, animal, and human that ever lived.
The paper was published Aug. 21 in Science Advances by UChicago Pritzker Molecular Engineering (PME) postdoctoral researcher Aman Agrawal and his co-authors—including PME Dean Emeritus Matthew Tirrell and Nobel Prize-winning biologist Jack Szostak, director of UChicago’s Chicago Center for the Origins of Life.
“This is a distinctive and novel observation,” said Tirrell.
Droplets and discovery
The research looks at “coacervate droplets”—naturally occurring compartments of complex molecules like proteins, lipids, and RNA. (In the early 2000s, Szostak started looking at RNA as the first biological material to develop, rather than DNA.)
The droplets, which behave like drops of cooking oil in water, have long been eyed as a candidate for the first protocells. But there was a problem, Szostak found in 2014.
It wasn’t that these droplets couldn’t exchange molecules between each other, a key step in evolution; the problem was that they did it too well, and too fast. Any droplet containing a new, potentially useful pre-life mutation of RNA would exchange this RNA with the other RNA droplets within minutes, meaning they would quickly all be the same.
There would be no differentiation and no competition—meaning no evolution. And that means no life.
“If molecules continually exchange between droplets or between cells, then all the cells after a short while will look alike, and there will be no evolution because you are ending up with identical clones,” Agrawal said.