Evolution's baby steps 'recreated'

Scientists have recreated what might have been the first step in the evolution of living cells four billion years ago.

In a series of experiments, they produced chemical cell-like structures enclosing RNA, the earliest genetic molecule thought to have appeared on earth.

RNA is believed to pre-date its close cousin, DNA, and proteins, the building blocks of living things. The molecule served both as an early genetic storage material and a catalyst for chemical reactions.

But there is a big problem with the "RNA world" hypothesis which proposes that cellular life began with RNA. Nature must have bottled up the chemical components of RNA in some kind of container, the equivalent of an early cell.

"A missing piece of the RNA-world puzzle is compartmentalisation. 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," said lead researcher Professor Philip Bevilacqua, from Pennsylvania State University in the US.

"This packaging needs to happen in a small enough space: something analogous to a modern cell."

Prof Bevilacqua's team demonstrated how this could have occurred early in the earth's history, without the fatty molecules that now make up cellular membranes.

The scientists generated simple non-living "cells" using a polymer compound called dextran.

Droplets of dextran in solution formed natural compartments into which RNA could be packed. The more densely the RNA was held, the more easily it produced chemical reactions.

"We noted an increase in the rate of chemical reactions of up to about 70-fold," said Prof Bevilacqua, whose research is published in the journal Nature Chemistry. "Most importantly, we showed that for RNA to 'do something', to react chemically, it has to be compartmentalised tightly into something like a cell."