A theory of the origin of life based on a protein-RNA hybrid gets new support

Chemists say they have solved a crucial problem for the theory of the origin of life, by demonstrating that RNA molecules can bind together short chains of amino acids.

The results, published in the journal, were supported Nature dated May 11, a modified version of the “RNA-based world” hypothesis, which proposes that before the evolution of DNA and the proteins it encodes, early organisms were made up of strands of RNA, a molecule that can store Genetic information – in the form of sequences of nucleosides: adenine, cytosine, guanine and uracil – and also plays the role of catalyst in chemical reactions.

Bill Martin, who studies molecular evolution at Heinrich Heine University in Düsseldorf, Germany, says of the discovery, “It will open up completely new avenues for understanding early chemical evolution.”

In its original version, the RNA-based world theory posited that life may have arisen in the form of complex primary RNA strands, which were able to copy themselves and compete with other strands as well. From developing the ability to form proteins and eventually pass their genetic information onto more stable DNA, however, exactly how this process occurs has remained an open question, in part because catalysts made from RNA alone are much less effective than enzymes. Based on the protein present in all living cells today, Thomas Karel, an organic chemist at Ludwig Maximilian University in Munich, Germany, comments: “Although the presence of catalysts has been discovered [مكونة من الحمض النووي الريبي]Its motivational capacity is very weak.

ribosome based on RNA

While Karel and his co-workers were working on this conundrum, an idea inspired by the role that RNA plays in the way all living things today make proteins came to them; A strand of RNA encoding a gene (usually transcribed from a sequence of DNA bases) passes through a large molecular machinery called the ribosome, which produces the corresponding protein by synthesizing its constituent amino acids one by one.

Unlike most enzymes, the ribosome itself is not only made up of proteins, but also contains parts of RNA, and these parts play an important role in the synthesis of proteins. Moreover, the ribosome contains modified versions of the usual RNA nucleosides, which are : adenine, cytosine, guanine and uracil, these exotic nucleosides have long been considered the possible remnants of a primitive soup.

By joining two strands of RNA normally found in living cells, Carrell’s team was able to synthesize a synthetic RNA molecule that contained two of these modified nucleosides. Then the team separated the two original RNA strands and came up with a new strand carrying its amino acid, and this strand was in the right position to form a strong covalent bond with the amino acid that was previously linked to the second strand, and the process continued Step by step, growing a short chain of amino acids, forming a small protein called a peptide, became attached to the RNA. Forming the bonds between the amino acids requires energy that the researchers saved by supplying the amino acids with various reactants in solution.

“This is a very exciting discovery, as it not only charts a new pathway for RNA-based peptide formation, but also reveals a new evolutionary role for naturally occurring modified RNA bases,” Martin says. The results indicate an important role for RNA in the origin of life, but without requiring that RNA can copy itself.

Lauren Williams, a biophysical chemist at the Georgia Institute of Technology in Atlanta, agrees: “If scientists can connect the origins of RNA with the origins of proteins so that they are not independent of each other, the calculations will change dramatically to support the hypothesis The world based on protein and RNA, and far from the hypothesis of the world based on RNA alone.”

In order to prove that this explanation is a reasonable explanation for the origin of life, scientists have to go through several more steps. The peptides made inside the team’s RNA consist of a random chain of amino acids, rather than a chain determined by the information stored inside the RNA, and Carrell says that larger structures of RNA might contain segments that “recognize” the shapes of the acids. Certain amino acids at specific sites, resulting in a specific structure, and some of these complex peptides synthesized on RNA may have the properties of catalysts, and be subject to evolutionary pressures to become more functional, and about this, Karel says: “If the molecule can copy itself, we will have It’s like a miniature living thing.”