December 4, 2021
Update: 12/04/2021 01:25 a.m.
The study of the origin of life is a fascinating and complex field and has disturbed scientists not only out of intellectual curiosity, but also as a way forward to understand our own origins.
One of the first to address this question was the philosopher Aristotle (384 BC – 322 BC) and solved it with his theory of spontaneous generation, according to which life is generated from inert matter. This theory was not refuted until the 19th century by the French scientist Louis Pasteur.
It is believed that the Earth formed exactly at the same time as the solar system, about 4.5 billion years ago now, and that for a long time there has been a continuous bombardment of meteorites, which together with the high geological activity, caused pressures generated. and temperatures so high that life was absolutely impossible.
The scenario began to change about 3.9 billion years ago when a stable hydrosphere appeared on our planet. In this liquid mass, dissolved molecules, mineral fragments and rocks appeared, as well as bubbles generated by gases expelled from underwater volcanoes.
Some four million years later, there were already different species of cells that began to “relate” to each other in a very archaic way. What made him go from an inhospitable, lifeless planet to the appearance of perfectly established living beings?
In an attempt to answer this question, in the middle of the last century, the American scientist Stanley l miller (1930-2007) carried out an experiment from which the components of the original Earth’s atmosphere (ammonia, hydrogen, methane and water vapor), with the participation of electric discharges that in some way simulated the energy contribution that existed before the appearance of life, they were able to react and produce organic compounds.
In other words, Stanley L Miller has shown that it is possible to generate basic biological molecules from simple chemical compounds.
The world of RNA
In the 1980s, it was shown and accepted that all living things originated from a single common ancestor who was baptized as LUCA – an acronym in English for “the only common universal ancestor” – and who lived about 3,500 million years ago, who carried out all the basic mechanisms of a living being.
LUCA was a nucleusless, single-celled living being with a lipid plasma membrane and a DNA genome. It is estimated that it could have around 600 genes and that bacteria, archaea and equariots have formed from it.
This is when a new question arises: what was the intermediate act between prebiotic chemistry and LUCA?
We know that proteins are encoded in DNA and that DNA replication cannot occur without the participation of active proteins.DNA polymerase‘. In a way, this pairing represents the chicken and egg paradox at the molecular level, being impossible to know if the first thing to appear in the theater of life was DNA or proteins.
Most likely it was neither, the first actor to appear on the stage had to be RNA. The explanation must be sought in that it is the only macromolecule sufficiently versatile to function as a genotype and phenotype. RNA is much more than an intermediary molecule in the flow of genetic information as has been believed for some time, since it is able to perform the functions of DNA and proteins.
Most likely, between prebiotic chemistry and LUCA there was what is now called the “RNA world”, that is, protocells with ribozymes, fatty acids in their membranes and a RNA genome.
Despite all that has been put forward in the knowledge of the origin of life, there are still many questions to be answered. For example, if RNA is a very sensitive molecule to hydrolysis, how is it possible that it was formed on a planet “overflowing” with water?
Pedro Gargantilla is an internist at the Hospital de El Escorial (Madrid) and author of several popular books.