A study conducted by Harvard University could provide the definitive clue to solving one of the most shocking enigmas about the origin of life on Earth: nature’s preference for left- or right-wing biomolecules.
Many organic compounds present a property called chirality, which consists in the existence, for the same molecule, of two forms that differ by the spatial orientation they adopt and that makes them non-superimposable. The example of our hands helps to understand this concept: contemplating them, we can immediately tell if it is the right or the left by the position of the thumb.
The two varieties of molecules that exhibit chirality behave differently when illuminated with polarized light: one bends light to the right, the other to the left. Therefore, in scientific terminology, these varieties are called right-handed and left-handed respectively.
Surprisingly, life on our planet is very selective in the use of biomolecules with varieties of left and right. This is the case of amino acids and also of the sugars that are part of nucleic acids (DNA and RNA, the molecules that, among other things, store and activate genetic information).
Amino acids are the building blocks of protein, and all organisms on Earth use only the left-handed varieties. Instead, life uses only the dextrorotatory (right-handed) forms of the sugars ribose (a component of RNA) and deoxyribose (a component of DNA).
Since, in the natural state, the right-hand and left-hand forms of the same molecule are mixed in equivalent proportions, there must have been a mechanism, on ancient Earth, that favored the presence of one of the varieties over the other for amino acids and for sugars in nucleic acids. A mechanism that must have been present, at least, in the places where the precursor chemical reactions of life took place.
There are various hypotheses as to what these mechanisms might have been, but many of them fail to explain the level of efficiency required to generate sufficient concentrations of the left-handed or right-handed forms.
In the study published in the journal Science Advances by a team of scientists from Harvard University, the process by which right-rotating sugars could have concentrated in shallow pools billions of years ago is suggested.
Researchers have experimented with ribose aminooxazoline, a compound that contains the sugar ribose and from which some of the components of RNA can be derived, and have verified that magnetized surfaces, depending on their polarity, can help to concentrate right-handed or left-handed varieties. very pure
Specifically, working with magnetite, an iron mineral with magnetic properties and very common in nature, they have managed to obtain mixtures of ribose aminooxazoline that are practically pure in only one of the chiral varieties.
At the time of its formation from cooling lava, magnetite acquires the polarity of the magnetic field existing at that time on Earth (it is known that the planet’s polarity has undergone frequent reversals throughout its history). Thus, deposits of magnetite under shallow pools or lakes could have established a preference for right-rotating ribose in mixtures of chemicals dissolved in water.
Despite the fact that this study represents a significant advance in understanding the chemical and physical processes that took place for the appearance of life, much remains to be discovered.
The experiments with aminooxazoline ribose and magnetite could explain the preponderance of the right-handed form of the sugar ribose, but the mechanism that favored the left-handed amino acids is still being investigated.
In addition, we do not have a definitive answer about where life appeared and different models are discussed: were lakes and pools of surface water the laboratories of nature? Or was it instead in the hydrothermal vents at the bottom of the early oceans that the chemistry of life was perfected?
