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DNA and RNA May Have Existed Together Before Life Began on Earth

The most complex cousin of RNA, deoxyribonucleic acid (DNA), could also have existed before life began on Earth, as revealed by recent US research.

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The most complex cousin of RNA, deoxyribonucleic acid (DNA), could also have existed before life began on Earth, as revealed by recent US research.

Chemicals from the United Kingdom and the United States have shown how both molecules – DNA and RNA – could have formed under conditions that were probably present in ancient Earth. By developing a previous study that demonstrated a method of building nucleic acid strands in a prebiotic environment, the team demonstrated how RNA can be converted into components of the DNA molecule in a few easy steps, without the need for enzymes.

“These new findings suggest that it may not be reasonable for chemists to be guided so strongly by the RNA World hypothesis in the investigation of the origins of life on Earth,” said Ramanarayanan Krishnamurthy of the Scripps Research Institute. Biologists have been advancing over the past half century in the hypothesis that the chemical machinery that makes up the first cells had its roots in RNA-based chemical reactions. Now, this new research was published in Nature Chemistry.

The simplest structure of RNA and its talent for mechanical work gives it an advantage in hypotheses that suggest that the first biochemical reactions were predominantly governed by a single versatile molecule. But researchers showed a few years ago that hybrid molecules were not as stable as the pure strands of RNA and DNA.

“It’s beginning to realize in the field that RNA and DNA could have been mixed initially, but then they separated according to the things they do best,” says Krishnamurthy.

That is, there could have been an unstable mixture of the two molecules until the pure DNA expired. Where does this richness of DNA molecules come from? Now, Krishnamurthy has an answer in the form of a sulphurous chemical substance called thiouridine.

Already implicated as a possible precursor of RNA, the team showed how the compound could potentially react in several stages to form deoxyadenosine, the sugar-coated spine of the DNA molecule bound to one of the bases of its genetic code.

Alternatively, a similar process could produce its chemical relative, deoxyribose. However, showing how a process could have happened is not the same as proving that it was carried out, so this is, at least for the moment, a key starting point to face new research on the subject.

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