Life's Origins Were Easier Than Was Thought

In the primordial soup that produced life on earth, there wereorganic molecules that combined to produce the first nucleic acidchains, which were the first elements able to self-replicate. Accordingto one of the more accepted theories, these molecules were ribonucleicacid (RNA) chains, a molecule that is practically identical to DNA andthat today has the secondary role in cells of copying informationstored in DNA and translating it into proteins. These proteins have adirect active role in the chemical reactions of the cell. In the earlystages of life, it seems that the first RNA chains would have had thedual role of self-replicating (as is today the case with DNA) andparticipating actively in the chemical reactions of the cell activity.Because of their dual role, these cells are called ribozymes (acontraction of the words ribosome and enzyme). But there is animportant obstacle to the theory of ribozymes as the origin of life:they could not be very large in length as they would not be able tocorrect the replication errors (mutations). Therefore they were unableto contain enough genes even to develop the most simple organisms.

An investigation led by Mauro Santos, from the Department of Genetics and Microbiology at the Universitat Autònoma deBarcelona (Spain), alongside two Hungarian scientists, has shown thatthe error threshold, that is, the maximum number of errors that mayoccur during the replication process of ribozymes without thisaffecting its functioning, is higher than was previously calculated. Inpractice, this means that the first riboorganisms (protocells in whichRNA is responsible for genetic information and metabolic reactions)could have a much bigger genome than was previously thought: they couldcontain more than 100 different genes, each measuring 70 bases inlength (bases are the units that constitute the genes and codify theinformation), or more than 70 genes, each measuring 100 bases. It isworth remembering that tRNAs (essential molecules for the synthesis ofproteins) are approximately 70 bases long.

The discovery has greatly relaxed the conditions necessary forthe first living organisms to develop. "This quantity of genes would beenough for a simple organism to have enough functional activity",according to the researchers. Recent analysis into the minimum numberof DNA genes required to constitute bacteria, the most simple organismtoday, considers that around 200 genes is sufficient. But inriboorganisms there can be much fewer genes, since DNA genomes includea number of genes that have the role of making the RNA translationsystem (which enables proteins to be produced) work, which would not berequired in RNA-based organism.