For decades, scientists have tried to figure out why the genetic basis for life on Earth involved 20 key amino acids, when just 13 would have been enough to jump-start the evolution of all the proteins we'd need.
Now, an international team of researchers has created a quantum chemistry model that explains what triggered the inclusion of the additional seven—a spike in the levels of oxygen in our biosphere, coupled with the discovery that the newer amino acids have a greater chemical reactivity than the older ones, meaning they're more adaptable. A paper describing the research was published in the journal Proceedings of the National Academy of Sciences.
Amino acids are considered the building blocks of life. DNA sequences encode each individual amino acid to build out our genetic code and create vital proteins; but we would only need the first 10 to 13 to do so, leaving the other seven rather superfluous.
Quantum chemistry, not to be confused with the better-known quantum computing or quantum physics, is a computerized method of calculating certain properties of matter, like a molecule's ability to conduct electricity or react to radiation.
"Biologists usually compare many big things [like animals] and deduce the underlying causes [like shared genes] whereas physicists usually start with small, precise things [like electrons] to explain emerging big phenomena [like reactivity]," coauthor Bernd Moosmann, a professor of biochemistry at the Johannes Gutenberg University Mainz, told Newsweek via email. "In our work, we have just mixed both approaches in one, and they have converged somewhere in the middle."
Moosmann and his colleagues created a quantum chemistry model that compared amino acids on Earth to amino acids from space that had arrived via meteorites. There's less to react to out in space than there is on Earth, so while in space the handful of older aminos might suffice, life inside our atmosphere required a little extra help. The researchers found that the younger the amino, the more reactive it is to external forces, making it more adaptable—an advantage in pretty much anything involving the evolutionary process. Moosmann said that as far as he's aware, no such approach has ever been taken before.
"The great thing about quantum chemistry is that one can calculate so many things without having the molecule at hand," Moosmann explained. "If someone anywhere on earth has determined a molecule's chemical structure, the rest can be calculated. In theory, those calculations could be accurate, but in reality...sometimes they are utterly wrong."
The newer aminos' reactivity still didn't account for their presence in the genetic tool box to begin with. The researchers conducted additional experiments which verified their theoretical results. They found that at least three of the newer aminos—methionine, tryptophan and selenocysteine—were included in response to the rising levels of oxygen in our atmosphere. Since oxygen encourages the production of toxic-free radicals, we needed additional, nimbler amino acids to react to those free radicals and help our cells repair themselves.
