What were the first genes made of? Many investigators believe that life’s initial genetic material was ribonucleic acid (RNA) instead of its current choice, deoxyribonucleic acid (DNA) (SN: 5/6/95, p. 279). While evidence for this RNA-world hypothesis has grown, some scientists have questioned whether nucleic acids with a backbone of ribose, or any other sugar molecule, would be stable enough to survive the harsh conditions of early Earth.
Noted origin-of-life investigator Stanley L. Miller of the University of California, San Diego and two colleagues have now offered evidence that peptide nucleic acid (PNA), a more stable alternative to RNA, may have existed during the world’s primordial days. In the early 1990s, scientists created this DNA mimic by combining nucleic acids with a protein backbone. Not long after, Peter E. Nielsen of the University of Copenhagen suggested that PNA might have preceded its less stable relative, RNA, as life evolved.
The question remained, however, whether natural conditions during Earth’s beginnings could synthesize PNA. Miller took up the challenge. His famous 1953 experiment showed that electric sparks in a mix of gases from the planet’s early atmosphere created amino acids and other organic molecules.
In the April 11 Proceedings of the National Academy of Sciences, Miller and his colleagues report shooting electricity through a blend of methane, ammonia, nitrogen, and water. The experiment created various parts of PNA—in particular, the molecule called AEG that forms its peptide backbone.
“The components of PNA are synthesized under potentially prebiotic conditions. This finding makes a plausible case that PNA might have been the first genetic material,” the authors conclude.