One of the fundamental processes of life is the replication of nucleic acids, DNA and RNA. This complex molecular mechanism makes it possible to produce, from a moleculemolecule initial, two identical daughter molecules. All terrestrial life is based on this process of replicationreplicationwhich allows us to regenerate our tissues, reproduce and evolve.
DNA replication: a well-known mechanism with very murky origins
The mechanism of replication is now well known. Very schematically, we consider that theADNADN and theARNARN are made up of two strands, wound into a helix. By separating, each strand of the parent molecule will serve as a template for the synthesis of a new strand. Two will thus reform double strandsdouble strands exactly identical.
However, there remain many gray areas, particularly regarding the origin of this mechanism. Given its fundamental role in biological processes, it is normal to consider that it must have intervened very early, at the very moment when the first building blocks of life appeared on Earth more than 4 billion years ago. However, it is not easy to imagine how this process got started in this primitive environment.
Hydrothermal sources: the temperature problem
It is indeed unlikely that it was initiated in the open ocean, where the dilution of the basic molecules is far too great. In this sense, the environment represented by hydrothermal sources, with their fluids loaded with elements essential to life, seems much more favorable. However, it presents another problem. We know in fact that the replication of nucleic acidsnucleic acids is favored by the presence of a gradientgradient thermal and that high temperatures tend to cause the degradation of these molecules. However, hydrothermal sources present rather high and, above all, very stable temperature conditions.
To address this problem, a team of researchers reproduced the conditions in the laboratory physiquesphysiques and chemicals that can be found within the porosityporosity rocks forming the chimneyschimneys hydrothermal. These rocks in fact form a major interface between two very different environments: on the one hand, hot, basic fluids loaded with gazgaz, metalsmetals et nutrientsnutrients miscellaneous ; on the other the ocean, cold, salty, acidic. Coupled with mineralsminerals present in rocks, which may have served as a catalyst for the synthesis of RNA or DNA, the physicochemical gradients present at this interface are considered by numerous studies to have played a major role in the establishment of the first chemical reactionschemical reactions at the basis of life and in particular the synthesis of nucleic acids. But how could this environment give rise to the replication process?
A tripling of the number of DNA strands in just 5 minutes!
In an article published in the journal eLifethe researchers propose a scenario. Their experiments reveal that the pores located at the intersection between a gas flow and a fluid aqueousaqueous could have presented the necessary conditions. In these tiny pockets within the rock, it appears that the nucleic acid molecules present in the aqueous phase would have accumulated at the gas-water interface, under the effect of evaporation induced by the arrival continues gas in this porosity. However, 5 minutes after the start of the experiment, the researchers observed a tripling of the number of DNA strands initially present. After an hour, there were 30 times more!
For the researchers, if the high concentration of nucleic acid molecules would have allowed replication, it is the gradient of salinitysalinity present within the pore which would have played in the mechanism of separationseparation strands. Tests have shown that when these conditions are not met (aqueous solutionaqueous solutiongas flow and salinity gradient), no replication was observed.
These conditions are completely in agreement with what can be observed at hydrothermal sources. Results which therefore further strengthen the idea that life appeared in this underwater volcanic context.
