What came first, RNA or DNA?

Representation of a DNA sequence of a person.CORBIS

This is an unanswered question at the moment.

We do not know of any living being today without DNA as its genetic material.

Only some viruses, which many scientists do not consider living beings because they need another organism to replicate, only have RNA.

For this reason, we might think that the first organism had to have DNA.

But DNA is a molecule with a more complex conformation than that of RNA (in a double-stranded helix instead of a linear chain) and with less functional versatility.

DNA needs another type of complex molecule, enzymes, which are proteins with catalytic activity, to replicate and transmit genetic information to daughter cells during cell division.

RNA, on the other hand, is a molecule that contains genetic information, but also has enzymatic capacity.

And, in theory, that would give it advantages to be the first genetic molecule.

But it is, on the contrary, a more unstable molecule.

Until fairly recently, most scientists agreed that the early world was an RNA world.

But there is no evidence that this was so.

There are recent works that explain the efforts that are carried out in many laboratories to be able to answer this question.

It is assumed that the original basic conditions were similar to those that can now be reproduced in a laboratory.

What is being done is trying to find in nature or build, without enzymes, polymers similar to those found in organisms, which are long macromolecules of DNA or RNA, from prebiotic monomers (nucleotides).

But this has not been achieved even by applying the external sources of energy that could have triggered these reactions, including lightning,

high temperatures or radiation.

That is, reproducing the possible conditions of that primitive world of volcanoes, storms, etc.

Nucleotides need all those tools that exist within the cell for the assembly to take place, also using the DNA of the mother cell as a model to make copies without errors.

In other words, replication only seems possible when the entire cellular mechanism is already assembled.

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Therefore, in my opinion, it is probable that the first organisms had some molecules that facilitated the union of nucleotides and the replication of DNA or RNA.

The genetic material is essential for life, without it the cells would not have the necessary information to build other necessary components or the hereditary transmission of this information.

Therefore, solving the question of whether DNA or RNA arose first has been of scientific interest since the discovery of these molecules.

It is even possible that it was almost simultaneously, or that its appearance depended on the previous existence of peptides or simple proteins.

But we must continue working to resolve these issues.

María Capa

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