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TUCSON, Ariz. — Four billion years ago, life on Earth faced a culinary challenge: how to build complex proteins from a limited pantry of ingredients. The solution — a universal genetic code — would become one of nature’s greatest inventions, used by virtually every organism alive today. However, new research suggests we’ve misunderstood how this cosmic cookbook came together.
“The genetic code is this amazing thing in which a string of DNA or RNA containing sequences of four nucleotides is translated into protein sequences using 20 different amino acids,” says Joanna Masel, senior author and professor of ecology and evolutionary biology at the University of Arizona, in a media release. “It’s a mind-bogglingly complicated process, and our code is surprisingly good. It’s nearly optimal for a whole bunch of things, and it must have evolved in stages.”
For decades, scientists believed they had a good handle on the order in which amino acids were added to life’s early recipe book. The prevailing theory suggested that the first amino acids were those readily available on early Earth, like those found in the famous Miller-Urey experiment that simulated primitive Earth conditions in 1952.
However, this new research, published in Proceedings of the National Academy of Sciences, suggests that this understanding is flawed because it relies on misleading laboratory experiments rather than evolutionary evidence. While valuable in demonstrating that nonliving matter could give rise to life’s building blocks through simple chemical reactions, these experiments had limitations. For example, the Miller-Urey experiment didn’t yield any sulfur-containing amino acids – not because they weren’t important to early life, but simply because sulfur wasn’t included in the experimental setup.
Led by Sawsan Wehbi, a doctoral student in the Genetics Graduate Interdisciplinary Program at the University of Arizona, the study takes a novel approach by examining protein sequences that date back to LUCA – the Last Universal Common Ancestor from which all current life descended.
“If you think about the protein being a car, a domain is like a wheel,” Wehbi explains. “It’s a part that can be used in many different cars, and wheels have been around much longer than cars.”
By studying these ancient protein patterns, the team has uncovered surprising evidence that some amino acids previously thought to be latecomers to life’s recipe book were actually among the first ingredients. They identified more than 400 families of sequences dating back to LUCA, with over 100 originating even earlier and showing signs of diversification before LUCA existed.
Perhaps most surprisingly, the research suggests that sulfur-containing amino acids like cysteine and methionine, as well as the metal-binding amino acid histidine, were added to the genetic code much earlier than previously thought. This is particularly significant because these amino acids play crucial roles in biological processes – especially in binding metals, which is essential for many of life’s chemical reactions.
“On worlds like Mars, Enceladus and Europa, where sulfur compounds are prevalent, this could inform our search for life by highlighting analogous biogeochemical cycles or microbial metabolisms. Such insights might refine what we look for in biosignatures, aiding the detection of lifeforms that thrive in sulfur-rich or analogous chemistries beyond Earth,” notes study co-author Dante Lauretta, Regents Professor of Planetary Science and Cosmochemistry at the University of Arizona, adding that the implications of these findings extend far beyond Earth.
The study’s methodology is particularly clever. Rather than relying on theoretical models of what might have been available on early Earth, the researchers looked at protein domains – functional units of proteins that can fold and function independently – that date back to LUCA. By examining how frequently different amino acids appear in these ancient protein sequences compared to more recent ones, they could infer which amino acids were available when these proteins first evolved.
The research revealed that smaller amino acids were generally added to the genetic code first. However, there were some fascinating exceptions to this rule. Methionine and histidine were added earlier than their size would suggest, while glutamine was added later. This makes sense when you consider the roles these amino acids play – methionine is crucial for a process called methylation that cells use to regulate their genes, while histidine is excellent at binding metals, which was likely important for early life’s chemical reactions.
Perhaps the most profound lesson from this research isn’t just about how life began, but about how science itself evolves. Just as life’s genetic code emerged through trial and error, our understanding of its origins continues to be refined and rewritten. And like the ancient ring-shaped molecules that early life seemed to favor, we’ve come full circle – back to the drawing board to rethink what we thought we knew about life’s first cookbook.
Paper Summary
Methodology
The researchers used sophisticated computational methods to analyze protein sequences from thousands of different organisms. They focused on protein domains – independent functional units within proteins – and used various statistical techniques to determine which domains dated back to LUCA. They then compared the frequency of different amino acids in these ancient proteins with their frequency in more recent proteins, using this information to infer the order in which amino acids were added to the genetic code.
Key Results
The study found that smaller amino acids were generally incorporated into the genetic code first, with some notable exceptions. Metal-binding and sulfur-containing amino acids were added earlier than previously thought, while glutamine was added later. The research also revealed distinct patterns in pre-LUCA proteins, suggesting they might have evolved under different conditions or used different genetic codes.
Study Limitations
The study relies on computational reconstruction of ancient protein sequences, which involves some uncertainty. The researchers acknowledge that their findings represent an approximation of the order in which amino acids were recruited into the genetic code, rather than an exact historical record.
Discussion & Takeaways
The findings suggest that the evolution of the genetic code was more complex than previously thought, potentially involving multiple competing codes before settling on the universal code we see today. The study also highlights the importance of metal binding and sulfur metabolism in early life, with implications for our search for life on other worlds.
Funding & Disclosures
The research was supported by various organizations including NASA’s Future Investigators in NASA Earth and Space Science and Technology program, the John Templeton Foundation, the Chan-Zuckerberg Initiative, and several other academic and research institutions. The authors declared no competing interests.
Sounds like typical main stream junk science to me. Their conclusions are not empirically supported by the findings. This is a common theme among the scientific community which is only funded when the “science” supports the narrative. Such as the Miller-Urey experiment they quote, which did not create “the building blocks of life.” There are two types of proteins– left and right handed and the Miller-Urey experiment only created right handed proteins. Living things contain only left handed proteins and if you add even one right handed protein to a living thing it dies. Furthermore, science has never demonstrated that macro-evolution is a fact. All fossils are complete organisms. There are no transitional fossils and the 4.5 billion year age of rocks is a number they grabbed out of thin air. Again, no empirical evidence that the Earth is as old as science claims while there is ample evidence that suggests the earth is only 6,000 to 10,000 years old.