While the blueprint of an organism is contained in its genetic code, it’s proteins that make life possible. The genes coded in your DNA become RNA, and that RNA becomes proteins. Whether you’re talking about a human being or a virus, all proteins on Earth use the same 20 amino acids. But why these molecules out of the hundreds of amino acid molecules that were floating around? To answer that question, the study recreated the conditions of Earth 4 billion years ago.
During Earth’s first billion years, evidence suggests that 10 “early” amino acids became prevalent thanks to an atmosphere of ammonia and carbon dioxide, combined with intense ultraviolet radiation. Space rocks also delivered some essential compounds to the planet, giving us the early amino acids. The second set of 10 came later, and this is where the research focused.
In the simulated environment, the team evaluated the solubility and secondary structure of numerous amino acids — that is, how they fit together to form proteins. Proteins aren’t just a string of amino acids. The molecules interact with each other, forming a 3-dimensional folded structure determined by charge, cross-linking, and hydrophobic effects. The team found a type of pre-biotic evolution can occur in which amino acids that offer better foldability become more common.
“Our research shows that nature could have selected for building blocks with useful properties before Darwinian evolution,” says Johns Hopkins chemist Stephen Fried. We know from the study of space that amino acids are common throughout the universe. The team speculates that the chemical selection of foldable amino acids prior to the development of complex life could mean a similar process happens on other planets.
Perhaps, then, if we find life someplace out there, it might not be terribly different from us. There is at least good evidence that it could be made of the same fundamental building blocks, and that gives us someplace to start.