Origin of homochirality in peptides: The first milestone at the origin of life

Abstract

Living organisms have some common structures, chemical reactions and molecular structures. The organisms consist of cells with cell division, they have homochirality of protein and carbohydrate units, metabolism, and genetics, and they are mortal. The molecular structures and chemical reactions underlying these features are common to all, from the simplest bacteria to human beings. The origin of life is evolutionary with the emergence of a network of spontaneous biochemical reactions, and the evolution has taken place over a very long time. The evolution contains, however, some “landmarks” and bottlenecks, which in a revolutionary manner directed the evolution, and the article establishes an order of some of these events. Recent articles show that peptides in living organisms are long-time unstable with loss of their secondary homochiral conformations and with D-amino acids. Based on these observations and an extensive scientific literature on Abiogenesis, we argue that the first milestone in the prebiotic evolution is at the emergence of homochiral peptides in an aqueous solution with a high concentration of amino acids and a lower water activity than in the cytosol in living organisms. The homochiral peptides in cytosol are unstable, and the long-time aging of peptides in the cytosol causes mortality of living organisms. The metabolism and genetics are established in an environment with homochiral peptides in the Earth’s crust for $\approx$ 4 Gyr ago at a lower water activity than in the cytosol in living organisms. Finally, the cells with cell division are established in the Hot Springs environment at the interface between the crust and the Hadean Ocean.