Every living thing we know, from the smallest bacterium to the largest blue whale, is based on the same magnificent genetic code, the universal blueprint that underlies the diversity of life on Earth. But our understanding of how this complex code evolved has sparked heated debate and ongoing scientific research.

Is the universal genetic code an ancient feature that emerged fully at the beginning of life, or is it the product of gradual evolution shaped by billions of years of adaptation and change? University of Arizona student Sosan Webi has provided compelling evidence that the widely accepted theory of how this genetic code evolved needs to be rethought. The answer, it turns out, lies not in how we translate the code, but in the order in which the building blocks, amino acids, are added.

Established views on the genetic code

“The genetic code is an amazing thing, in which a set of DNA or RNA containing sequences of four nucleotides is translated into protein sequences using 20 different amino acids,” said Joanna Masel, senior author of the study.

“This is an incredibly complex process, and our code is surprisingly good. “It’s almost ideal for a lot of things, and it probably evolved in stages.”

The team’s findings contradict the conventional wisdom that early life favored smaller, simpler amino acid molecules. The study shows that complex molecules are also added. The researchers also found that amino acids that bind to metals were incorporated into the genetic code earlier than thought. This opens up a whole new perspective on how the genetic code emerges.

Rethinking laboratory approaches

The generally accepted view of the evolution of the genetic code is based largely on laboratory experiments that attempted to recreate early Earth conditions, particularly the famous Yuri-Miller experiment of 1952. However, as valuable as this experiment was, it also had its limitations. As a result of the experiment, no sulfur-containing amino acids were found, despite the presence of this element in large quantities on the early Earth.

This lack of sulfur has led many to believe that sulfur amino acids are introduced into the genetic code at a later stage. But as critics have pointed out, this is not surprising given that sulfur was not included in the Yuri-Miller experiment.

Search for life beyond Earth

The sulfur-rich nature of early life creates exciting opportunities for astrobiology, according to study co-author Dante Lauretta, a professor of planetary science and cosmochemistry in the university’s Lunar-Planet Laboratory.

“On sulfur-dominated worlds such as Mars, Enceladus and Europa, this could advance our search for life by shedding light on similar biogeochemical cycles or microbial metabolism,” Professor Lauretta said.

New insights into the genetic code

Researchers at the University of Arizona took an innovative approach to analyze amino acid sequences related to our hypothetical common ancestor LUCA, which lived approximately 4 billion years ago. Unlike previous studies, they focused on protein domains (shorter lengths of amino acids) rather than full-length protein sequences.

“If you think of protein as a car, space is like a wheel. This is a part that can be used in many different cars, and wheels have been around much longer than cars,” Webey said.

Using statistical data analysis tools, they were able to track the incorporation of individual amino acids into the genetic code. More importantly, the team found that the ancient sequences contained amino acids with aromatic ring structures, such as tryptophan and tyrosine, even though they were late additions to our code.

“This points to other genetic codes that predated our own and have since been lost in the depths of geological time,” Masel said. “Apparently they took a liking to rings from an early age.”

This breakthrough not only transforms our understanding of early molecular evolution, but also paves the way for investigating how genetic systems might arise on other planets. The evolution of the genetic code, which previously appeared to be well studied, now once again opens up exciting new possibilities for future research and discovery. The full text of the research was published in the journal Proceedings of the National Academy of Sciences.