Currently, it is understood that all living organisms share a common genetic code. However, the origins and timeline of this code remain contentious topics in the scientific community.
Researchers at the University of Arizona propose that our comprehension of the genetic code’s evolution requires significant revision.
Sawsan Wehbi and Joanna Masel have introduced a novel hypothesis in the journal Proceedings of the National Academy of Science. They argue that the sequence in which amino acids, the building blocks of the genetic code, appeared is quite different from the current scientific consensus.
Masel stated: “The genetic code is an amazing system in which sequences of three nucleotides, known as codons, in a string of DNA or RNA are translated into protein sequences using 20 different amino acids.”
“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.”
The researchers suggest that the essential components of our proteins, amino acids, trace back to four billion years ago at the time of the ‘last universal common ancestor’ of all life on Earth.
This ‘last universal common ancestor’ (LUCA) is considered the progenitor of all subsequent life forms.
The scientists argue that previous studies are outdated and flawed as they are based on laboratory experiments rather than evolutionary processes.
For example, the older theory is based on the renowned 1952 Urey-Miller experiment, which sought to replicate early Earth conditions and investigate the potential origins of life, according to Phys.org.
These experiments failed to detect amino acids containing sulfur, despite the element’s plentiful presence on early Earth.
Consequently, the notion that sulfuric amino acids were incorporated into the genetic code at a later stage may be incorrect.
Employing modern technology and data from the National Center for Biotechnology Information, the researchers constructed a tree of protein domains leading back to LUCA, which were identified in the 1970s, prompting a reassessment of the emergence order of the 20 amino acids.
Wehbi illustrated: “If you think about the protein being a car, a domain is like a wheel.”
“It’s a part that can be used in many different cars, and wheels have been around much longer than cars.”
The study indicates that the existing genetic code likely emerged after other, now-extinct codes.
The researchers identified over 400 families of protein sequences dating back to LUCA, with more than 100 predating LUCA and diversifying before its emergence.
These sequences featured more amino acids with aromatic ring structures.
Masel concluded: “This gives hints about other genetic codes that came before ours, and which have since disappeared in the abyss of geologic time.”
“Early life seems to have liked rings.”