04.06.2015 09:36
The first living cells on Earth have not only RNA, and proteins capable of living in the hot water of the primary ocean planet, and without which the assembly of these complex molecules would be impossible. This is stated in an article published in the journal Proceedings of the National Academy of Sciences, reports The Softcraze.
Previously, scientists believed that the role of proteins and DNA in the first living organisms on earth playing RNA molecules . Over time, they began to control cellular processes proteins, as well as a repository of genetic information taken DNA. Charles Carter of the University of North Carolina at Raleigh says that “cooperation” between the RNA and peptides are likely needed for the spontaneous development of the variety of chemical complexity, which is typical for modern living world. « We believe that life on the early Earth was a world of proteins and RNA, and RNA is not just the world », – he told.
Today, biologists experimenting with short RNA molecules, trying to reproduce the process of the origin of life in the laboratory. Two teams of American biologists conducted experiments in his lab, trying to understand how the transition was made from the RNA world to the “tandem” of DNA and proteins.
The researchers said that the problem is the instability of the protein molecules. They are in a constant state only in a very narrow range of basic chemical parameters. If at least one of them is violated, the three-dimensional protein molecules usually breaks or deforms. This property of proteins is one of the main reasons why scientists had to come up with “RNA World” – the primary Earth’s oceans could be too warm to protein molecules it might normally exist. Carter and Volfenden check whether it is studying the behavior of amino acids in unusual temperature.
These experiments made it possible to get unexpected results. It was found that the difference in the physical properties of the amino acids and the way they interact with the nucleotides and were similar at 25 degrees Celsius, the optimum temperature for life, even at 100 degrees. Because of this protein will be “phased out” in three-dimensional molecule of the same rules as in the warm water and in boiling water, suggesting the possibility of their existence in the hot primary ocean Earth.
A confirmation of this, scientists have found transport RNA molecules in which amino acid capture and transfer them to the center of the assembly of proteins in the cell. As it turned out, tRNA contain two amino acid recognition systems, one of which focuses on the size of the molecules, and the second – how well they repel water.
The first is the “tail” tRNA for which It clings amino acid and consists of four genetic “letters”, the combination of which allows you to encode just 24 different molecular size. The second is located at the top of the tRNA, the so-called anticodon of three nucleotides, which clings to the decodable chain of genetic information.
The existence of such a double system of selection of amino acids, according to the authors, it suggests that the evolution of proteins was in two phases during the origin of life.
The first of these, they said, was completed before the advent of DNA, and while protein molecules are arranged simply – in single lines and simple two-dimensional structure. To build such structures was enough to know the dimensions of amino acids, which appear to be encoded in the RNA molecules of the body time “RNA world”. These proteins appear to have played a supporting role and help stabilize cell RNA molecules.
The emergence of a new “information carrier” – the DNA – and the related possibility to distinguish amino acids and their degree of hydrophobicity allowed to make quality of life step forward and begin to use complex three-dimensional structure of the protein, resulting in life acquired the appearance that it has today, the scientists conclude.
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