One of the most fascinating challenges of science is to investigate how life emerged on Earth so far back in its early days. Under what conditions must the basic components of a more complex life be formed? One of the main answers is based on the so-called concept of RNA world, which was proposed by molecular biology pioneer Walter Gilbert in 1986. According to this hypothesis, nucleotides are produced from “primitive soup” and short RNA molecules are produced by nucleotides. These so-called oligonucleotides have been able to encode a small amount of genetic information.
Because such single-stranded RNA molecules can also be combined into double strands, however, this gives rise to the theoretical prospect that these molecules can replicate themselves. In each case, only two nucleotides are bound together, which means that one chain is the exact counterpart of the other, thus forming a template for the other.
In the process of evolution, this replication may be improved and produce more complex life at some point. Thomas Carell, a chemist at the University of Munich, said: “the idea of RNA World has a big advantage. It outlines a path in which complex biological macromolecules, such as nucleic acids with optimized catalysis and information coding properties, can emerge. As we understand it today, genetic material is made up of double strands of DNA, a slightly modified, durable macromolecular form of nucleotides. “
However, this hypothesis is not without problems. For example, RNS is a very fragile molecule, especially when it gets longer. In addition, it is not clear how the connection between RNA molecules and the protein world is formed, and as we know, genetic material provides a blueprint for it. As reported in a new paper published in the journal Nature, Carell’s team has found a possible way to make such a connection.
RNA itself is a complex macromolecule. In addition to the four classical bases A, C, G and U that encode genetic information, it also contains non-classical bases, some of which have very different structures. These non-informative nucleotides are very important for the operation of RNA molecules. Researchers now know more than 120 of these modified RNA nucleosides, which nature has incorporated into RNA molecules. They are most likely relics of the former RNA world.
Carell’s team has now found that these non-classical nucleosides are key ingredients that, like it, connect the RNA world to the protein world. According to Carell, some of these molecular fossils, when located in RNA, can be decorated with a single amino acid or even a small chain of amino acids (peptides) & quot; itself. When amino acids or peptides happen to exist in the same solution as RNA, this leads to a small chimeric RNA- peptide structure. In such a structure, amino acids and peptides linked to RNA then even react with each other to form larger and more complex peptides. “in this way, we have created RNA- peptide particles that encode genetic information in the laboratory, and even form lengthened peptides,” Carell said.
Therefore, the ancient fossil nucleosides are somewhat similar to the nuclei in RNA, forming a core on which long peptide chains can grow. On some strands of RNA, peptides even grow at several points. “it was a very surprising discovery,” Carell said. “it is possible that there has never been a pure RNA world, but RNA and peptides coexist in a common molecule from the very beginning. Therefore, we should extend the concept of RNA world to the concept of RNA- peptide world. Peptide and RNA support each other in their evolution, and new ideas are put forward. “
According to the new theory, a decisive factor in the beginning is the existence of RNA molecules, which can “decorate” themselves with amino acids and peptides to connect them into larger peptide structures. “RNA has slowly evolved into an ever-improving amino acid linking catalyst,” Carell said. The relationship between RNA and peptides or proteins remains to this day. The most important RNA catalyst is the ribosome, which still connects amino acids to grow peptide chains today. As one of the most complex RNA machines, it is responsible for translating genetic information into functional proteins in each cell. “as a result, the RNA- peptide world solves the problem of chicken or egg, & quot;Carell said. “this new idea creates a foundation on which the origin of life gradually becomes explainable.”