According to a new study published in nature on May 11, chemists have solved a key problem in the theory of the origin of life. They have proved that RNA molecules can connect short chain amino acids together** Bill Martin, who studies molecular evolution at the University of Dusseldorf in Germany, said the discovery opened up a broad and fundamental new way to explore early chemical evolution.
The study supports another statement based on the "RNA world" hypothesis, which holds that the first organism was based on RNA strands before the evolution of DNA and its encoded proteins. The standard theory holds that in the "RNA world", life may exist in the form of complex primitive RNA strands, which can not only copy themselves, but also 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 occurs remains a question, in part because the efficiency of catalysts composed of RNA alone is far lower than that of protein enzymes found in all living cells today. Thomas Carell, an organic chemist at the University of Munich in Germany and corresponding author of the study, believes that although RNA catalysts have been found, their catalytic ability is very poor.
Researchers are inspired by the fact that RNA, which encodes all the amino acids in the ribosome, usually plays a role in the formation of a protein sequence.
Unlike most enzymes, ribosomes themselves are composed not only of proteins, but also of RNA fragments, which play an important role in the synthesis of proteins. In addition, ribosomes contain modified versions of standard RNA nucleosides a, C, G and U.
By connecting two segments of RNA common in living cells, the researchers constructed a synthetic RNA molecule, including two modified nucleosides. At the first specific nucleoside site, the synthetic molecule can bind to an amino acid, and then the amino acid laterally binds to the adjacent second specific nucleoside. Subsequently, the researchers isolated the original RNA strand and introduced a new RNA strand, which carries its own amino acids and forms a strong covalent bond with the amino acids previously attached to the second strand.
Step by step, this process produces a short chain of amino acids, the mini protein peptide, which is attached to RNA. The formation of chemical bonds between amino acids requires energy. Researchers provide energy by stimulating amino acids with various reactants in solution.
Martin said it was a very exciting discovery. "Not only does it indicate a new path for the formation of RNA based peptides, the discovery also reveals the new evolutionary significance of naturally occurring RNA modified bases." Martin added that the results suggest that RNA plays an important role in the origin of life.
Loren Williams, a biophysical chemist at Georgia Institute of technology, agrees. He believes that if the origin of RNA and the origin of protein are linked, and their emergence is not independent, it will fundamentally turn to support the "RNA protein world" and stay away from the "RNA world".
In order to prove that this is a reasonable origin of life, scientists must further complete several steps. The peptides formed on the RNA of the team are composed of random sequences of amino acids, not determined by the information stored in the RNA. Carell said that larger RNA structures can be folded into shapes that "recognize" specific amino acids at specific locations, resulting in specific structures. These complex RNA peptide mixtures may have catalytic properties and become more efficient under the influence of evolutionary pressure. Carell believes that if molecules can replicate, similar micro organisms will be produced.
Author: Xin Yu source: China Science Daily