Where did the first biomolecules that gave rise to life come from? In addition to the terrestrial origin of the building material, delivery from space now appears increasingly likely: according to new study results, peptides could form on icy space dust more effectively than previously thought. The water, which is commonly found in space, apparently does not have a strong inhibiting effect on the reaction, according to the experiments under simulated space conditions.
Ages ago, certain molecules on our planet linked together to form ever more complex compounds – until life processes finally started. To put it simply, this is how evolution is said to have begun on Earth. However, the question arises as to how and where the basic biological building blocks could have originated. In addition to a terrestrial origin, space is also considered a possible source for the biologically relevant substances: meteorites could have brought organic molecules to Earth that played a role in the emergence of life. This potential was also confirmed by findings of amino acids, nucleobases and various sugar substances in meteorites.
On the trail of possible complexity
However, the question of how complex organic molecules can become in space remained open for a long time. Researchers led by Serge Krasnokutski from the Astrophysical Laboratory of the Max Planck Institute for Astronomy at the University of Jena provided the first indications of this two years ago: their experiments showed that peptides could also form on cosmic dust grains. These are central basic substances of life: the complex molecules consisting of interconnected amino acids are responsible for many biological reactions and form the framework material of cells. Through experiments under simulated space conditions in vacuum chambers, Krasnokutski and his colleagues were able to show that peptides can be formed from ammonia, atomic carbon and carbon monoxide.
But so far it has remained unclear how effective the reaction on icy particles in space could be. It was to be assumed that water molecules, which are usually also abundant in the material of the dust grains, inhibit the formation. With their new experiments, Krasnokutski and his colleagues have now explored the extent to which this is actually true. “We recreated the conditions that exist in space in a vacuum chamber and added the substances that occur in so-called molecular clouds,” says Krasnokutski. The researchers examined the reaction products using the mass spectrometry method.
Inhibited but still effective
As Krasnokutski explains, the reaction of ammonia, atomic carbon and carbon monoxide under the experimental conditions initially produces chemical precursors of amino acids: so-called aminoketenes. These then combine to form longer chains – they form polypeptides. The potentially critical aspect of water now comes into play, says Krasnokutski: When the individual aminoketenes are linked, water is released. However, if water is already present in the substance mixture, it can be assumed that the process will be inhibited. The scientist emphasizes again: “Most interstellar dust grains are covered with water-containing molecular ice.”
Therefore, the initial assumption was sobering from an astrobiological perspective: peptides are only formed to a small extent in space, if at all. But as the team reports, the analysis results of the reactions involving water now show: “Our mass spectrometric studies, which were possible at the University of Poitiers, showed that the presence of water in the molecular ice slows down the formation of peptides by fifty percent – but they still arise,” says Krasnokutski. As he emphasizes, this ultimately results in a very effective formation of the biomolecules: “If you look at the time scales on which astronomical processes take place, this slowdown is almost negligible,” says the scientist.
Apparently peptides could form to a relevant extent in space and could also reach planetary surfaces via meteorites. But what do the results mean specifically for the history of the origins of life? They cannot answer whether the basic molecular building blocks of biology were of terrestrial or extraterrestrial origin. But at least the study now confirms the possibility that a “cosmic seeding” once took place.
Source: University of Jena, specialist article: Sciences Advancesdoi: 10.1126/sciadv.adj7179