2018-10-07 11:09:42
In the previous article I talked about the mystery of the difference between bacteria and archaea in the use of glycerol molecules, which are chiral. Let us remember that chiral molecules (from the Greek kheir, hand) are chemically identical, that is, they are composed of the same atoms, but they are mirror images of one another. The chiral glycerol mystery is actually a concrete form of the more general mystery of why living things use only one of two classes of chiral molecules, named D (dextro, right) and L (levo , left). Although D and L molecules are formed in equal amounts in chemical reactions, sugars are usually, with very few exceptions, all of the D series, while the amino acids that make up proteins are, also with very few exceptions, of the D series. class L. Why? What physical and chemical phenomena led to the selection of one of the chiral forms for the molecules of life? How did life select only one of the forms of that balanced mixture between the D and L classes?
So far, we had interesting ideas, but very little evidence to solve this mystery. One of the recent proofs, however, is the discovery that the carbohydrate molecules detected in asteroids and bodies of the solar system are preferentially of the D form, that is, they coincide with the chiral form used by living organisms. If life derives from the arrival of these molecules on Earth, after collisions with asteroids and comets, and their subsequent evolution, this could explain the chiral preference for life of at least carbohydrates, although it would still remain to explain why. those molecules created in space have a chiral imbalance, as well as the chiral preference of L-amino acids and other molecules of living beings.
One of the ideas that had been proposed to try to explain the chiral preference of the large molecules of life was that chemical aggregation reactions, which achieve the union of some amino acids with others, occurred in swirling flows to the right or to the left, leading to selection. of only one of the chiral molecules of an equilibrium mixture of the two forms D and L. These eddy flows form in the drains of our houses, for example. According to this hypothesis, the eddy flow in one direction or another would influence the spatial position of the chiral molecules in that flow and would lead to the preferential selection of one or another chiral form of the molecules to generate the final molecular aggregate, so that this It would be formed by only one of the shapes of the molecules of the initial mixture, D or L.
Today, it is believed that the origin of life took place in hydrothermal vents. These are like geysers or fumaroles on the ocean floor that expel very hot water, of geothermal origin. The expelled water contains dissolved minerals that solidify as they come into contact with the cold ocean water, thus creating solid structures, such as chimneys, that can reach several meters in height. These mineral structures are very porous, similar to pumice.
A few years ago, it was published that the pores of hydrothermal vents were capable of concentrating molecules inside, thus enabling the progression of chemical reactions at speeds sufficient to generate precursors of living molecules). Now, a group of researchers from the Chinese Academy of Sciences proposes that the flow of hot water emitted by hydrothermal vents, when entering through these pores, also creates rapid microeddies that rotate in one direction or the other. The researchers have devised a device that contains micro-enclosures where the flow creates eddies in one direction or another. Analysis of the aggregates that formed indicated that they had indeed acquired chirality according to the direction of the microeddy that had formed.
However, additional studies will be necessary to demonstrate that this was what happened, but, although we are still far away, little by little we are getting closer to the goal of understanding what could have happened at the origin of life.
References:
Jiashu Sun (2018). Control over the emerging chirality in supramolecular gels and solutions by chiral microvortices in milliseconds. Nature communications, 9:2599 | DOI: 10.1038/s41467-018-05017-7.
The origin of life through the Looking Glass.
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Kilo of Science Volume I. Jorge Laborda
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Chained circumstances. Ed.Lulu
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One Moon one civilization why the Moon tells us we are alone in the universe
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