- 13 May 2009 by Kate Ravilious
- Magazine issue 2708. Subscribe and get 4 free issues.
CREATING life in the primordial soup may have been easier than we thought. Two essential elements of RNA have finally been made from scratch, under conditions similar to those that likely prevailed during the dawn of life.
The question of how a molecule capable of storing genetic information - even DNA's simpler cousin RNA - could ever have arisen spontaneously in the primordial cooking pot has perplexed scientists for decades. RNA consists of a long chain composed of four different types of ribonucleotides, which each consist of a nitrogenous base, a sugar and a phosphate.
Most people assumed that these three components first formed separately, and then combined to make the ribonucleotides. The only trouble was that it seemed impossible that two of the four bases with particularly unwieldy chemistry ever reacted spontaneously with the sugar.
To tackle this problem, John Sutherland from the University of Manchester, UK, tried to work out a new recipe for RNA that gets by without forcing isolated bases and sugar molecules to react. His team experimented by cooking up ribonucleotides from five small molecules thought to be present in the primordial soup. "We started with the same building blocks as others, but take a different route," Sutherland says.
And this time the cooks seem to have got it right. The recipe and conditions that they came up with to mix the five ingredients - including a good blast of UV light - produce ribonucleotides via a joint precursor molecule that contains both the base and the sugar instead of making each in their free form (Nature, DOI: 10.1038/nature08013).
This package deal sidesteps the problem of getting two unwilling partners to react, but only thanks to another trick, say the researchers. The reaction worked only when phosphate was present right from the start, although it does not react with the mixture until near the final stages. It turns out it is needed as a catalyst and as a chemical buffer early on.
"We don't use any way-out scenarios - all the conditions are consistent with what we know about early Earth," says Sutherland. William Scott, from the University of California in Santa Cruz agrees: "It's a great leap forward that demonstrates how prebiotic RNA molecules may have assembled spontaneously from simple and presumably relatively abundant constituents."
The need for UV light suggests life didn't begin in a submarine vent, one possible scenario. Instead, it points towards a warm pond - an idea first mooted by Charles Darwin, who knew nothing of RNA.
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