Source: Nature.com
Researchers have studied the reactions that produce sugars of two or three carbon atoms (fuel for the organism), amino acids (the pieces with which proteins are built), ribonucleotides (the basic elements of RNA, the nucleic acid that carries the genetic information) and glycerol (the elementary unit of lipids). The conclusion of this study is that all these molecules could have formed on the surface of the Earth starting only with hydrogen cyanide (HCN), hydrogen sulfide (H2S) and ultraviolet radiation from the Sun.
It had previously been shown that ribonucleotides can be formed from the HCN derivatives, but it was not explained where this HCN could arise from. Patel's team has assumed that life arose when meteorites were bombarding primitive Earth, so cyanide could be formed by the reaction of meteorite carbon with the nitrogen in the atmosphere. Meteorites also usually contain iron sulphide and the metal sulphides dissolve in the cyanide solutions, so the presence of HCN ends up favoring the appearance of hydrogen sulfide. In 2013 it was shown that H2S and HCN can form metabolic sugars.
What the researchers now show is that H2S and HCN in the conditions of the primitive Earth can give rise to more than 50 different molecules. Glycerol and 11 different amino acids now bind to biomolecules that have already been synthesized, including cytidine and uridine ribonucleotides, and small sugars. Many of these reactions have yields that range between 40 and 70%. For us to make a composition of place of the importance of these numbers consider that in the famous experiment of Miller and Urey of the primordial soup on the origin of life the performance of the reactions that gave rise to the amino acids detected was less than 1 %; in these experiments an electric spark passed through a mixture of methane, ammonia, hydrogen and water. The network of reactions of Patel et al. It is incredibly efficient.
This efficiency comes in part because the reagents are added one after another, instead of mixing them all at once from the beginning. The team of researchers justifies this procedure because of the possibility of water running down slopes carrying different molecules to different currents and ponds.
This work, extremely elegant from the chemical point of view, has its main weak point, like all hypotheses about the chemical origin of life, in the initial conditions it assumes. Finding high levels of HCN and H2S by the simple fall of meteorites does not seem very solid and there is no current evidence to show that this is the case. On the other hand, the known biochemical routes do not coincide with those found. And yet, this work seems very important to us: it has been shown that the existence of a complex and convergent network of chemical reactions that gives rise to biomolecules from only two very simple molecules is possible. No doubt this will mark many future investigations.
Reference:
Bhavesh H. Patel, Claudia Percivalle, Dougal J. Ritson, Colm D. Duffy & John D. Sutherland (2015) Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism Nature Chemistry DOI: 10.1038/nchem.2202
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