Has the origin of life conundrum been solved?

Chuck Bednar for redOrbit.com – @BednarChuck

The interdependence of genetic material, proteins, and fatty lipids have long created a sort of paradox when it comes to trying to figure out how life on Earth originated, but a new study has proposed that all three factors originated from a pair of simple compounds.

In the study, which was published online in the journal Nature Chemistry, researchers from the University of Cambridge explain that precursors of ribonucleotides (RNA), amino acids and lipids can all be derived simple reactions involving hydrogen cyanide and its derivatives.

As a result, they continue, all of the cellular subsystems may have arisen simultaneously through common chemistry centered around the reductive homologation of the compound. The key parts of the reaction are driven by ultraviolet light, use ​hydrogen sulfide as the reductant, and are sped up by Cu(I)–Cu(II) photoredox cycling, the authors wrote in their new paper.

[STORY: How chirality affects the origins of life]

In other words, as Science staff writer Robert F. Service explains, these compounds (which were abundant on the early Earth) can undergo a series of simple reactions that produce the three main categories of biomolecules required to kick-start life: nucleic acids, amino acids and lipids.

One geological setting

While the research does not concretely prove how life on Earth originated, it does help solve an apparent paradox in which RNA or DNA are required to provide blueprints for making proteins, but those genetic molecules cannot be copies without proteins, and neither of those can function without the membranes provided by fatty lipids that hold a cell’s contents together, which in turn cannot be synthesized without protein-based enzymes encoded by genetic molecules.

Jack Szostak, a molecular biologist and origin-of-life expert at Massachusetts General Hospital in Boston who was not part of the study, told Service that the new study was “a very important paper. It proposes for the first time a scenario by which almost all of the essential building blocks for life could be assembled in one geological setting.”

Which came first?

Different groups of scientists have long submitted theories based on which of the biomolecules they believed came first, Service noted. Some believe that RNA served as a protein-like chemical catalyst that sped up reactions, while metabolism-first advocates believe organic building blocks created by simple metal catalysts that led to the development of the other biomolecules.

A study published in the journal Nature in 2009 by many of the same chemists involved in the new paper reported that the simple precursor compounds known as acetylene and formaldehyde were able to undergo a sequence of reactions to produce two of the four nucleotide building blocks of RNA, demonstrating how the nucleic acid may have formed without needing enzymes.

That begged the question: how did acetylene and formaldehyde form themselves? Where did they come from? So John Sutherland from the Medical Research Council (MRC) Laboratory of Molecular Biology in Cambridge and his colleagues worked backwards from those compounds to see if they could discover some way to produce RNA using even simpler base materials.

No resemblance to modern biochemistry

In the new study, Sutherland and his colleagues report that they were able to create nucleic acid precursors starting with just hydrogen cyanide, hydrogen sulfide and UV light. Furthermore, they report that the conditions required to produce RNA precursors also created the starting materials necessary for natural amino acids and lipids to form, Service explained. In short, they found one set of reactions that could have created the building blocks of life at the same time.

Nick Lane, an origin-of-life biochemist at University College London, told Chemistry World that the reactions described in the study were “impressive” and that Sutherland and his co-authors were “building a coherent set of ideas.” However, he added that the scenario as a whole was not convincing, and that the reaction network “bears no resemblance to modern biochemistry.”

[STORY: The building blocks of life may be found on Jupiter's moon Europoa]

“The entire network would have had to be overwritten,” he said, adding that the “geochemical context” was “improbable” because it “calls on very high cyanide concentrations and there’s no evidence to back that up.” Lane added that the study demonstrated that it was “not so hard” to generate complex metabolic networks, and that “the onus is on those who disagree with this particular context to do equivalent experiments [simulating] more realistic environments.”

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