RNA is in fashion … for 3.8 billion years

RNA, a central molecule in biology

The analysis at the molecular level of all known living beings, and specifically the comparison of their genomes, has shown great similarities between them. This showed, more than forty years ago, that the three great branches of the tree of life (bacteria, archaea and eukaryotes) come from the same ancestor.

We know that species (or, perhaps, that community of them) as “last universal common ancestor” (LUCA, acronym formed by its initials in English) and it is estimated that it could have lived about 3.7 billion years ago (Ma ), just 800 million after the Earth and Moon formed.

LUCA already had the main characteristics that appear in all current biology, and based its operation on three key molecules: DNA (genetic information archive), proteins (catalytic molecules or enzymes, responsible for metabolism, and also structural), and RNA (intermediary in the flow of genetic information, which occurs in the sense DNA → RNA → Proteins).

RNA is a nucleic acid, a polymer made up of units or monomers called ribonucleotides. These can be of four types: A, C, G and U. Its most stable structure is the single chain, instead of the double helix characteristic of DNA.

However, even if it is a single chain, any RNA molecule folds over itself when it is in solution, because its monomers tend to recognize each other following the AU, GC and GU rules. Thus, RNA ends up forming more or less complex structures, which allows it to perform various functions in cells. In fact, the RNA → Proteins step is carried out by different types of RNA:

  • The genetic information, previously copied (transcribed) from DNA, is in the form of mRNA (as used in the vaccines discussed).
  • Its translation into proteins is carried out in ribosomes (aggregates of ribosomal RNA, rRNA, and proteins)
  • The so-called transfer RNAs (tRNA) also participate in this information decoding process.
  • Furthermore, the entire flow of genetic information is regulated by other RNA molecules.

RNA also constitutes the genome of a large number of “replicative entities” that cannot be considered authentic living beings, but that are fundamental in evolution due to their continuous interaction with the cells they parasitize: many families of viruses (including coronaviruses ), and also simpler plant pathogens called viroids.

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