The study supports an alternative claim based on the “RNA world” hypothesis, which holds that the first organisms were based on RNA strands before DNA and the proteins it encodes evolved. Standard theory holds that in an “RNA world,” life may exist as complex strands of primitive RNA that can both replicate themselves and compete with other strands. Later, these “RNases” may have evolved the ability to make proteins and eventually convert their genetic information into more stable DNA.
But how this process happens remains a question, in part because catalysts consisting of RNA alone are far less efficient than the protein enzymes found in all living cells today. The study’s corresponding author, Thomas Carell, an organic chemist at the University of Munich in Germany, believes that although RNA catalysts have been discovered, they are poorly catalyzed.
In studying this conundrum, the researchers were inspired by the role that RNA plays in making proteins in all modern organisms: The RNA strands that code for genes (usually copied from DNA base sequences) pass through ribosomes, which are created at a time An amino acid that forms the corresponding protein.
Unlike most enzymes, the ribosome itself is composed not only of proteins, but also of RNA fragments that play an important role in synthesizing proteins. In addition, ribosomes contain modified versions of the standard RNA nucleosides A, C, G, U.
The researchers created a synthetic RNA molecule that includes two modified nucleosides by linking two pieces of RNA commonly found in living cells. At the first specific nucleoside site, the synthetic molecule can bind to an amino acid, and then the amino acid side shifts to bind to the adjacent second specific nucleoside. The researchers then isolated the original RNA strand and introduced a new RNA strand that carried its own amino acids and formed strong covalent bonds with the amino acids previously attached to the second strand.
Step-by-step, this process creates a short chain of amino acids, mini-proteins, peptides, that attach to the RNA. The formation of chemical bonds between amino acids requires energy, which the researchers provided by exciting the amino acids with various reactants in solution.
Martin said this was a very exciting discovery. “Not only does it point to a new pathway for the formation of RNA-based peptides, the discovery also reveals new evolutionary implications for naturally occurring RNA-modified bases,” Martin added, adding that the results suggest that RNA played a role in the origin of life important role.
Loren Williams, a biophysical chemist at the Georgia Institute of Technology in the United States, agrees, arguing that if the origin of RNA and the origin of proteins are linked, and their emergence is not independent, then this fundamentally turns in favor.” RNA-Protein World” and away from the “RNA World”.
To prove this is a plausible origin of life, scientists have to go a few steps further. The peptides formed on the team’s RNA were made up of random sequences of amino acids, not determined by the information stored in the RNA. Larger RNA structures can fold into shapes that “recognize” specific amino acids at specific locations, resulting in defined structures, Carell said. These complex RNA-peptide mixtures may have catalytic properties and are subject to evolutionary pressures to become more efficient. Carell believes that if molecules can be replicated, similar micro-organisms could be created.
Author: Xin Yu Source: Chinese Science Journal