The history of evolution has repeatedly witnessed the eternal controversy about what was the first - an egg or a chicken - but one of the most interesting mysteries is as follows: was there life before the appearance of nucleic acids? And within the framework of the new study, scientists provided evidence that primitive biochemistry was able to appear and develop without phosphates - one of the most important and key structural components of nucleic acids that make up our genetic chemistry - which adds weight to the assumptions that even before the appearance of life already could exist a metabolism.
Scientists from the Massachusetts Institute of Technology and Boston University have identified a number of alternative metabolic pathways that do not require the participation of phosphates. The discovery can fill gaps in our understanding of how complex organic chemistry spawned life on our planet.
What we are accustomed to call life today is largely based on not quite perfect replicating chemistry, where there is a need for a template that can be copied, as well as a certain amount of energy that is enough for the physical transformation of simple carbon-based chemicals into more complex forms . And the question here is what was first: a chemical code that could evolve into a more complex form, or more complex ways that could use energy to convert simple chemicals into more complex organic compounds.
According to the so-called RNK world hypothesis, freely floating ensembles of ribonucleic acid molecules (RNAs), which functioned as storage for genetic information and were some kind of templates, accelerated the processes of chemical reactions that can now be described as the process of the emergence of life. The question in this concept is that RNA molecules could not do this without the energy source necessary for a sequence of chemical reactions, which, in turn, could be considered as an early form of metabolism (metabolism). In addition, RNA molecules contain phosphates - substances that are densely entwined in the environment and, therefore, difficult to integrate into organic compounds.
According to another hypothesis, the earliest forms of metabolic chemistry that were not bound by cell membranes initially had the possibility of absorbing energy from the environment - in the form of heat or light - and transferring it from one chemical reaction to another inside the organic soup (the kind of primary broth in which it originated a life). Eventually, this primitive metabolism (metabolism) merged with RNA molecules and was in this state until it found shelter inside individual fatty bubbles - molecules that could now be considered as the first cells.
And yet, energy metabolism in modern organisms is based around such compounds as adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADP), that is, again linked to phosphates.
Alternative metabolic pathways, which were identified by scientists in the new study, are based on molecules based on sulfur-a substance that was abundant in the terrestrial oceans several billion years ago.
"The importance of this research is that now, in the context of new attempts to find out the origin of life, the probability of its appearance without the participation of phosphates, which are now considered one of its most important components, but which might not have been, should be taken into account when the first chemical the reactions that led to its appearance, "says researcher Daniel Sergee from Boston University.
The idea that sulfur could once play a central role in the metabolic process is by no means new. As early as the beginning of the 20th century, the German chemist Wachtershauser suggested that the compounds of iron sulfide and nickel sulphide could play the role of a catalyst for the process of carbon fixation around deep oceanic volcanic flows and act as a mechanism for energy exchange between what they called "primordial organisms". However, the lack of convincing evidence, combining the variety of chemical reactions involved in this "sulphide-iron hypothesis", did not confirm this assumption.
"What was always missed was the lack of convincing evidence based on the evidence that these early chemical processes could be a connected and relatively complex primitive metabolic network, and not just scattered reactions," comments Serge.
Sergé and his team applied the method of computational system biology - a theoretical approach, in which mathematical models were used to study a variety of ways of biochemical reactions - and identified a set of eight phosphate-free compounds that could be abundant in the ancient oceans of our planet. Then they applied an algorithm for simulating primitive energy metabolism, including iron sulfides, as well as sulfide-containing compounds-thioethers-and began to monitor what various chemical reactions might occur with them.
As a result, it was found that the result of the main network of 315 reactions involving 260 metabolites could be the production of a variety of complex organic compounds necessary for the emergence of life. The list of these compounds also includes amino acids and carboxylic acids.
Since early bioorganic chemistry could not leave enough evidence of its existence in the form of ancient deposits, it is necessary to use similar mathematical models capable of predicting what could have happened many billions of years ago. And although such data can hardly be used as evidence of life-free life development, they can be one of the proofs of the possibility that life has emerged from chemical compounds that most modern organisms do not at all rely on. In addition, the use of such data can go far beyond the usual discussion of questions about how life on this planet could have formed.
"The analysis of metabolism from the point of view of the ecosystem level or even as a planetary phenomenon, and not as an individual feature of specific organisms, can be of practical importance for our understanding of the microbial community," says Serge.
The results of the research group of scientists from the Massachusetts Institute of Technology and Boston University was published in one of the latest issues of the scientific journal Cell.
The article is based on materials .
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