14 DAY TRIAL // For a long time, researchers have been fascinated with how complex life was able to evolve in the first place. From the primordial soup, a mix of amino-acids and basic RNA molecules, proteins, and eventually more complex structures developed, over millions and billions of years. Expert Stanley Miller was the first to demonstrate that basic chemicals could form amino-acids and even proteins, when subjected to electrical sparks. Now, a new model shows how the first genetic systems evolved from the primordial soup, ScienceDaily reports.
In charge of the new experiments was a team of physicists from the Rockefeller University (RU), led by the Head of the university's Laboratory of Experimental Condensed Matter Physics, Albert J. Libchaber. Its model shows how simple molecules can come together to form more complex structures, under the influence of natural factors. These include the earliest versions of the atmosphere, and the oceans, as well as electrical phenomena such as lightning.
“All these molecules have different properties and these properties define their interactions. What are the constraints that allow these molecules to self-organize into a code? We can play with that,” Jean Lehmann, a postdoctoral fellow in Libchaber's lab, says. She is also the first author of a study detailing the model, which appears in the June issue of the open-access scientific journal PLoS ONE. The experts explain that the genetic code is a triplet code. This means that, for every “letter” on messenger RNA, there is a correspondent in the 20 amino-acids that form proteins.
Proteins have evolved to be produced to fulfill only a specific function inside organisms. In charge of converting genetic information into proteins are molecular adapters called transfer RNA (tRNA). Messenger RNA is essentially made up of triplet sequences of letters, and these formations are known as codons. These codons can only bind to tRNA carrying exactly the opposite codon. Therefore, each codon-anticodon complex corresponds to a single amino-acid. Chains of the acids are formed as codons continuously bind to each other. Their order dictates the function of the amino-acids.
The problem early on in the Earth's history was that tRNA did not have the ability to distinguish between correct and incorrect codon-anticodon pairs. This means that, at that point, complex life was very unlikely to occur. The new, simple, theoretical system was developed in order to test if certain conditions might have led to the disappearance of random translation and to the emergence of the specific kind, between well-defined codon-anticodon pairs. Researchers used two basic amino-acids, two primitive tRNA, and an RNA template.
The model switched between various concentrations of each component, searching for the optimum conditions to create specific translation. “It takes a lifetime for the tRNA to dissociate from its codon. If it takes the amino acid loaded on the RNA longer than a lifetime to polymerize to an amino acid nearby, the selection of tRNA and amino acid doesn’t occur. But when the two lifetimes are comparable, even when there is nonspecific loading of an amino acid, a selection process begins to take hold because some amino acids would be more adaptive during that time span – and start what would be the beginning of a code,” Libchaber concludes.