Newly Discovered Primitive Xeno Nucleic Acids: A Valuable Addition to Understanding the Origin of Life

The mystery of the chemical origin of life on Earth has intrigued scientists for years. Numerous hypotheses have been proposed to explain the emergence of life and the role of genetic polymers in the process. Genetic polymers are materials composed of repeating chemical units that can store and transmit information. Understanding the synthesis of these polymers under primitive conditions is a crucial step in unraveling the origins of life.

One hypothesis, known as the RNA world hypothesis, suggests that RNA may have been the original genetic polymer. RNA could have served as a means for storing and transmitting genetic information, as well as for catalytic functions. However, the synthesis of RNA under primitive conditions without specialized circumstances has proven to be inefficient.

While the RNA world hypothesis remains plausible, it is likely that other forms of nucleic acid polymerization also occurred. One potential candidate is a nucleic acid called “pre-RNA,” which may have preceded RNA on early Earth.

To explore the origins of genetic polymers, a team of researchers from the Tokyo Institute of Technology, led by Research Scientist Ruiqin Yi, investigated the co-polymerization of glycol nucleic acid (GNA) monomers and dicarboxylic acids (DCA) under primitive conditions. Their groundbreaking study, published in Chemical Communications, revealed the synthesis of linear and branched xeno nucleic acid co-polymers.

“Research suggests that pre-RNA molecules could have been formed by linking monomers with other functional polymers, creating complex macromolecular structures,” explains Dr. Yi. “This interconnectivity not only enhances the complexity of the polymers but may also confer novel or emergent functions. Co-synthesis of polymers can provide insights into the origin of genetic molecules before the emergence of enzymes or RNA.”

The team reacted GNA monomers containing thymine and adenine bases with various substituted and unsubstituted DCAs through dehydration synthesis. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS) was employed to analyze the synthesized products. The results demonstrated the formation of alternating linear co-polymers with unsubstituted DCAs and both linear and branched co-polymers with substituted DCAs. The length and branching of the polymers could be controlled by adjusting the DCA/GNA ratio, temperature, and reaction pH.

Furthermore, the team discovered that a mixed reaction of GNA monomers with tartaric acid produced polymers containing both thymine and adenine, which are capable of base-pairing. These findings suggest a plausible pathway for the formation of short-chained polymers capable of storing and transmitting genetic information, similar to RNA or other primitive nucleic acids.

The results of this research indicate that branched and linear GNA-DCA-based xeno nucleic acid co-polymers could have been abundant on early Earth, depending on the composition of prebiotic organic molecules. Differences in chemical composition could have led to variations in the abundance of branched and linear informational polymers.

“In addition to the formation of non-canonical xeno nucleic acids through simple dehydration, our study reveals that these polymers, which contain complementary bases, possess information storage properties,” concludes Dr. Yi. “We are now delving deeper into the potential functions of these co-polymers and hope to gain more insights into the types of polymers that existed and functioned in the early stages of life.”

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