Ingenious chemistry shows how nucleotides may have formed in the primordial soup.
Richard Van Noorden
An elegant experiment has quashed a major objection to the theory that life on Earth originated with molecules of RNA.
John Sutherland and his colleagues from the University of Manchester, UK, created a ribonucleotide, a building block of RNA, from simple chemicals under conditions that might have existed on the early Earth.The feat, never performed before, bolsters the 'RNA world' hypothesis, which suggests that life began when RNA, a polymer related to DNA that can duplicate itself and catalyse reactions, emerged from a prebiotic soup of chemicals.
"This is extremely strong evidence for the RNA world. We don't know if these chemical steps reflect what actually happened, but before this work there were large doubts that it could happen at all," says Donna Blackmond, a chemist at Imperial College London.
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The start of something special?
Although Sutherland has shown that it is possible to build one part of RNA from small molecules, objectors to the RNA-world theory say the RNA molecule as a whole is too complex to be created using early-Earth geochemistry. "The flaw with this kind of research is not in the chemistry. The flaw is in the logic — that this experimental control by researchers in a modern laboratory could have been available on the early Earth," says Robert Shapiro, a chemist at New York University.
Sutherland points out that the sequence of steps he uses is consistent with early-Earth scenarios — those involving methods such as heating molecules in water, evaporating them and irradiating them with ultraviolet light. And breaking RNA's synthesis down into small, laboratory-controlled steps is merely a pragmatic starting point, he says, adding that his team also has results showing that they can string nucleotides together, once they have formed. "My ultimate goal is to get a living system (RNA) emerging from a one-pot experiment. We can pull this off. We just need to know what the constraints on the conditions are first."
Shapiro sides with supporters of another theory of life's origins – that because RNA is too complex to emerge from small molecules, simpler metabolic processes, which eventually catalysed the formation of RNA and DNA, were the first stirrings of life on Earth.
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