Origin-of-life researchers face a deceptively straightforward question: how did simple chemicals produce complex biochemistry? The complexity of this starts to come in when you consider the many complex biomolecules that would have been useful or essential to the first biochemical reactions. And it gets worse when you consider that there are lots of simple organic chemicals that plausibly could have been present on the early Earth. Figuring out which reactions to even start looking at can be a real challenge.
The extent of that challenge was highlighted a few years back, when a Cambridge lab suggested most earlier researchers had gone down a dead end. Previously, researchers tried to build up a sugar and a nucleic acid base separately, and then link to them to form precursors of DNA and RNA. But the group from Cambridge showed it was possible to build relatively simple compounds into a three-ring chemical that could then be converted into cytosine, an RNA component. Now, they’ve revisited that work and shown that all of the precursors of that reaction can be made with little more than cyanide.
The reaction the group reported back in 2009 only required a set of two or three carbon precursors, but these molecules were already somewhat complex: cyanamide, cyanoacetylene, glycolaldehyde, and glyceraldehyde. We don’t know that all of these chemicals would be common on a pre-biotic Earth, which leaves its relevance to the origin of life a somewhat open question.
In a new paper, the same lab tackles forming the simple, two- and three-atom sugars used in their earlier work (glycolaldehyde and glyceraldehyde). To get there, they started with nothing more complex than hydrogen cyanide, a simple molecule comprised of one atom each of hydrogen, carbon, and nitrogen. Hydrogen cyanide forms readily under a variety of conditions, and has been found on several bodies in our Solar System, as well as in the interstellar medium.
The authors were intrigued by reports in the literature of a cycle that involves a set of six cyanide molecules, coordinated by two copper atoms. In a water solution, this complex can cycle, driven by ultraviolet light, through a set of reactions that alternately spit out cyanide, protons, and electrons. These electrons get temporarily attached to water molecules, and typically end up being taken up by a scavenger molecule, usually nitrate. However, some reports in the literature noted that, when nitrate isn’t added to the reaction, some undefined larger molecules formed.
The authors went back and checked these reaction products, and found that they included both glycolaldehyde and glyceraldehyde—the two chemicals that were key building blocks of the reaction that produced the RNA precursor. And all the reaction required was copper ions and some UV light.
If left to continue cycling, the products of the reaction also included some more complex, five-atom ringed structures that incorporate nitrogen and oxygen in the ring. But the authors suspect that with the right conditions—namely the ones identified in the earlier paper—the products of this new cycle could be sent directly on to form cytosine. They also suggest the addition of other metals could shift the products to additional chemicals that may have biological relevance.
Hopefully, it’s safe to assume the lab already has these projects in the works.
View Original Source: Simple reaction makes the building blocks of a nucleic acid | Ars Technica