Researchers solve mystery of life's building blocks
06 February 2018
For decades scientists have wondered why the existence of life on earth depends on 20 amino acids, which are directed by DNA to form proteins, when only 10 to 13 of the essential amino acids could suffice.
"Researchers have been puzzled for decades why evolution has selected these 20 amino acids for genetic encoding," said Bernd Moosmann of the Institute of Pathobiochemistry at Johannes Gutenberg University Mainz, in a recent press release.
"The presence of the last and newest seven amino acids is particularly hard to explain, because suitable and functional proteins can be assembled using just the first and oldest 10 to 13 amino acids."
It is one of the most enduring mysteries of biochemistry, and scientists believe it solving it could help to shed light on the origins of life itself.
Moosman and fellow researcher Matthias Granold, approached the problem from a different perspective, by comparing the quantum chemistry of amino acids from space (such as those brought in by meteorites), with all of the amino acids used by life on earth.
Quantum chemistry applies the principles of quantum mechanics to the behaviour of atoms in chemical reactions. The approach not only allowed the researchers to look at the ways amino acids are spatially structured, but also at how their chemical reactivity might impact their roles, and the findings turned out to be significant.
The scientists found out that the extra 7-10 amino acids are ''soft'' meaning they are more easily repairable after oxidation. Early in the life of our planet increases in oxygen levels would have posed a significant risk to evolving life, due to the fact that oxygen promotes the formation of toxic free radicals, which can expose organisms and cells to massive oxidative stress. They point out that at least three of the amino acid add-ons that today form the fundamental building blocks for all life - methionine, tryptophan and selenocysteine - are "soft," in that they are more easily repairable after oxidation.
There is less to react to out in space than therefore life on earth needs to have more adaptability.
They found that the younger the amino, the more reactive it is to external forces, which makes it more adaptable - an advantage in pretty much anything involving the evolutionary process.
The researchers further found life on earth needed additional, nimbler amino acids to react to those free radicals and help our cells repair themselves.