The appearance of cell membranes represents a crucial milestone in the origin and early evolution of life on Earth, since they are responsible for maintaining stable conditions inside cells, protecting both genetic material and metabolic machinery, in addition to regulating the transport of substances. Although this layer of all cells is made of phospholipids, there is still a great debate surrounding their primordial nature and the very origin of phospholipids.
Now an international scientific team of astrophysicists, astrochemists and biochemists, led by the researcher Victor M. Rivilla of the Center for Astrobiology (CAB, CSIC-INTA), has just made a discovery of great importance for astrobiology: the first detection in space of ethanolamine (NH2CH2CH2OH), a molecule that contains four of the six chemical elements essential for life. The study is published in the journal PNAS.
Ethanolamine, a component of the phospholipids that make up the cell membrane, has been detected in a molecular cloud in our galaxy, and could have been transferred to early Earth via asteroids.
Ethanolamine can act as a precursor to the amino acid glycine, and is also part of the simplest phospholipids (and the second most abundant) that make up cell membranes.
The discovery of this important prebiotic molecule has occurred specifically in the molecular cloud G + 0.693-0.027, located near the center of our galaxy, using the radio telescope IRAM 30 meters in diameter from Pico Veleta (Granada) and 40 meters from the Yebes Observatory (Guadalajara).
As Rivilla points out, “these results suggest that ethanolamine is efficiently synthesized in interstellar space in molecular clouds where new stars and planetary systems are formed.”
Researchers have found that the abundance in the interstellar medium of ethanolamine relative to that of water indicates that ethanolamine was probably formed in space and could later be transferred to the granules that form the ethanolamine. asteroids, from which meteorites come.
“We know that a wide repertoire of prebiotic molecules could have reached early Earth through the bombardment of comets and meteorites,” he says. Izaskun Jiménez-Serra, a CAB researcher and co-author of the study.
“We estimate that around a billion trillion liters of ethanolamine could have been transferred to early Earth through meteoric impacts. This is equivalent to the total volume of Lake Victoria, the largest in Africa by area ”, adds Jiménez-Serra.
Simulations of the early Earth
Experiments simulating chemical conditions on early Earth confirm that ethanolamine may have contributed to the production of the simplest phospholipids in those early days on our planet.
For the co-author Carlos Briones, CAB researcher in biochemistry and molecular biology, “the availability of ethanolamine on early Earth, along with glycerol, phosphate groups, and fatty acids or alcohols, may have contributed to the evolution of early cell membranes; and this has important implications not only for the study of the origin of life on Earth, but also on other habitable planets and satellites within the solar system or anywhere in the universe ”.
The availability of ethanolamine and other molecules on early Earth may have contributed to the evolution of early cell membranes, and this has important implications for studying the origin of life on Earth and other worlds.
The discovery of ethanolamine adds to the important contributions that the CAB has made in the field of chemistry in the interstellar medium, including the first detections in space of other molecules of great astrobiological interest, such as hydroxylamine or thioformic acid. .
The search in the interstellar medium for precursor molecules of prebiotic chemistry will continue in the coming years. “Thanks to the improvement in the sensitivity of current and next-generation radio telescopes, we will be able to detect increasingly complex molecules in space that could give rise to the three basic molecular components of life: lipids (which form the membranes), the nucleic acids RNA and DNA (which contain and transmit genetic information), and protein (which are responsible for metabolic activity) “, says Rivilla, who concludes:” Understanding how these prebiotic seeds are formed in space could be key to understanding the origin of life. “
Recent detection of indene in space
For their part, researchers from the CSIC’s Institute of Fundamental Physics (IFF) have also recently confirmed for the first time the unequivocal presence of indeno (c-C9H8), a polycyclic aromatic hydrocarbon (PAH), in the interstellar medium. Specifically in an unexpected place: the dark cold taurus cloud or TMC-1.
Heiles Cloud 2, which is part of the Taurus molecular cloud (Taurus Molecular Cloud (TMC). / Grand Mesa Observatory, Colorado (USA), Terry Hancock and Tom Masterson
PAHs are organic compounds formed by rings, with a very bad reputation on earth because, for the most part, they are the result of the combustion of oil and coal and are toxic to humans. However, in space they have another role that, despite needing confirmation, may even be related to the origin of life.
In the observations made of the interstellar medium there are infrared bands that, until now, it was not known with certainty what they could be. The hypothesis was being considered (for more than 40 years) that it was precisely polycyclic aromatic hydrocarbons, but definitive confirmation was lacking.
Indene, a polycyclic aromatic hydrocarbon, has also been detected for the first time in an unexpected place in space: the cold dark cloud of Taurus.
At first it was thought that PAHs could form in circumstellar envelopes around evolved stars. These stars are in the final stages of their life and expel much of their matter into the interstellar medium. In fact, 20 years ago, benzene, an aromatic ring present in many PAHs, was detected for the first time in the hot regions illuminated by ultraviolet light around an evolved star, which suggested that the formation of these hydrocarbons requires temperatures high and ultraviolet light.
The presence of PAH in the interstellar medium, therefore, would have an exogenous origin. That is, it would form in circumstellar environments and would later be transported to the interstellar medium by stellar winds.
However, the first detection has been carried out in an unforeseen place: the cold prestellar core of TMC-1, which is well protected from ultraviolet radiation. In this environment, in addition to indene, the presence of Ethinyl cyclopropenylidene (c-C3HCCH) and of cyclopentadiene (c-C5H6). It should be noted that cyclopentadiene and indene, molecules made up of rings of five and six carbon atoms, are, despite their large size, exceptionally abundant.
“With these observations, not only is the presence of PAH definitively demonstrated in the interstellar medium, but it is also confirmed that they are formed in situ and from less complex molecules, that is, they are not transported from other environments (for example, on the surface of the dust grains), but they are formed according to what is called bottom-up, from the bottom up, from smaller molecules that come together in the gas phase ”, explains the researcher José Cernicharo, from the IFF-CSIC and lead author of the study, published in Astronomy & Astrophysics.
Confirm relationship with origin of life
Although some theories relate PAHs to the origin of life, more studies are still necessary to corroborate the role they may have played in the creation of nucleobases, which are part of RNA. While waiting for more data that may or may not confirm this possibility, this work represents a major step forward in studies that seek to explain the mechanisms of complex molecule formation, which remain, for the most part, a mystery.
The observations of TMC-1 have also been carried out with the 40-meter radio telescope of the Yebes Observatory, of the National Geographic Institute (IGN), and have been possible thanks to new receivers built within the framework of a European project.
Victor M. Rivilla et al. “Discovery in space of ethanolamine, the simplest phospholipid head Group”. PNAS, 2021.
(Two of the co-authors, C. Briones and I. Jiménez-Serra, coordinate the research challenge The origins of life: from chemistry to biology within the strategic theme Origins, (co) evolution, diversity and synthesis of life in the Books CSIC 2030 targets).
J. Cernicharo et al. “Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene and indene”. Astronomy & Astrophysics, 2021
(Study framed within the Nanocosmos project funded by the European Research Council)