Author’s Note: This article was written in collaboration with Vincent Kofman, a co-author of the reviewed paper and a postdoctoral fellow at NASA’s Goddard Space Flight Center
Amino acids are one of the most important building blocks of life as we know it. In the core they contain an amino and an acid group, through which they can combine with other amino acids. This linking process can form long chains, which makes them form proteins. In humans, 20 different amino acids all make up proteins, and the difference between them lies in the molecular side chain between the amino and acid groups. The different groups create links in the chain and fold them into highly specific shapes so that the proteins can perform highly specific tasks ranging from metabolism to muscle movement and cell duplication.
Given that their presence is a necessary, if not necessarily sufficient, condition for the development of life, scientists have spent many decades exploring where they first formed. With an article published in Nature Astronomy last month, they took a step closer to that understanding by discovering that it is possible to form glycine, the simplest amino acid, in the star nurseries of interstellar clouds.
The evolution of glycine in such an inhospitable environment had previously been theorized. In particular, glycine was observed in samples from comet Wild 2, which had returned from the Stardust mission, as well as in observations of the comet from comet 67P / Churymov-Gerasimenko. Since comets formed together with the solar system from the same original starting material, they are a window into this solar system in earlier years. Glycine was seen in these windows, so scientists speculated that it could have formed in the basic material shared by both comets and the solar system itself.
Amino acids in interstellar space.
Credit AGU Youtube Channel
A team led by Sergio Ioppolo from Queen Mary University set out to form glycine in the conditions of the interstellar gas clouds in which stars, planets and comets are born. Their work reflected another famous chemistry experiment that was looking for the molecules needed for the origins of life – the Miller-Urey experiment. In this work, scientists attempted to restore conditions believed to have existed on early Earth by throwing together a “primordial soup” of chemicals and adding lightning to the mixture. Under these conditions, Miller and Urey found a pile of organic molecules that could be the precursors of the first sparks of life.
Dr. Ioppolo and his team tried to answer the same question, but examined very carefully how these essential molecules of life are formed. They built an ultra-high vacuum chamber and lowered the temperature to 10 to 20 degrees Kelvin to mimic the conditions in dark interstellar gas clouds. They then placed chemicals known to be present in these interstellar clouds, such as carbon monoxide, ammonia, and methane. Then they exposed the frozen chemicals to unbound atoms, which triggered chemistry similar to what they did under dark cloud conditions. Like magnets clicking together, the atoms broke the existing chemicals apart, allowing their components to recombine in a unique way.
Discussion of interstellar clouds and dark nebulae by JPL scientists.
Photo credit: ScienceMagazine Youtube Channel
The chemical conditions in dark clouds are very different from those here on Earth. The density of the particles is a million times lower and the temperatures are so low that almost everything freezes solid. Under these conditions, molecules form atom by atom, and like Lego bricks, certain molecules can be built from scratch. By re-establishing these conditions in the laboratory, scientists can find out which chemical reactions are likely to take place and which molecules are likely to form.
The work of Dr. Ioppolo and his team did just that, showing that glycine can form under the conditions that occur in these dark corners of space. Similar to the sun, most of the material in dark clouds consists of helium and hydrogen. Hydrogen can exist as an H2 molecule and as an unbound atom.
Formation of glycine from the atoms and molecules in the interstellar gas clouds.
Photo credit: Ioppolo et al.
The unbound atom is highly reactive and initiates chemistry with almost everything it encounters. It combines with other atoms and builds molecules like CH4 (methane), NH3 (ammonia). In the intermediate stages of this hydrogen bombardment, the precursor chemicals CH3 and NH2 can react to form CH3NH2, methylamine. Methylamine is a precursor to glycine and was found in abundance in Comet 67P. This finding most likely leads directly to the finding of glycine abundance in the same comet.
Youtube video with details about glycine.
Photo credit: Unacademy NEET Youtube Channel
Hydrogen can not only produce methane or ammonia, it can also react with CO2, which is also abundant in the layers of ice in the dark clouds. If this is the case, the carbon atom can form a different bond. Sometimes this extra bond with methylamine forms, resulting in glycine. In the experiments described in the most recent publication, the peculiarities of these reactions were examined and the frequency of the glycine formed in these reactions was calculated. The calculation shows that the amount of glycine formed is sufficient to enrich planets such as early Earth with prebiotic molecules and to facilitate the emergence of life.
After the chemical proof of concept is demonstrated, scientists can draw on the numerous implications this work has for both existing theories and future studies. The paper shows that it is possible that the building blocks of life result from natural processes that take place prior to star formation and that enrich the raw materials of the planets with the essential building blocks of life. Although these molecules may not survive the harsh events of planet formation, the fact that they may be present in the raw materials of stars and planets suggests that their abundance is widespread throughout the universe.
Discussions about amino acids in space.
Photo credit: SciShow Youtube Channel
Although only glycine was found in the experiments described in the publication, the detection of the formation of the amino acid backbone also opens the way for the formation of other amino acids. Previous research has shown that the central carbon atom that carries the group that gives amino acids their function is most likely targeting reactions that take place in the same ice in which they are formed. This indicates that the other biologically relevant amino acids can also form under the same conditions.
The study also leads to some other interesting questions. If the glycine is there, how can we detect it directly? Under the right circumstances, telescopes can detect glycine when it is heated and gasified. As new stars heat the surrounding material, the original ice is melted and the constituents can be detected using ground-based observatories such as the Atacama Large Millimeter Array (ALMA) in Chile. A deep look into these star kindergartens revealed a complex chemistry and taught us a lot about the formation of stars and planets.
This photo of the ALMA antennas on the Chajnantor plateau in Chile, more than 5000 meters above sea level, was taken a few days before the start of the ALMA Early Science and shows only a group of the 66 dishes. ALMA observes the sky in sub-millimeter light, a part of the spectrum that is invisible to the human eye and lies between infrared and radio waves. Photo credits: ALMA (ESO / NAOJ / NRAO) / W. Garnier (ALMA)
Naturally, if the building blocks of life are in the raw materials of stars and planets, what is the probability that life is in other places in the Milky Way? If our solar system alone contains a handful of planets and moons on which life could be possible, we can only imagine how many planets and stars there are that could house life. In the appropriate context, this better understanding of the formation of the building blocks of life has some amazing implications for the potential abundance of life across the galaxy.
Nature – A non-energetic mechanism for glycine formation in the interstellar medium
Queen Mary University of London – the building blocks of life can form long before stars
Sci News – Amino Acids Can Form Long Before Stars and Planets: Study
C & EN – Interstellar glycine search intensified
PhysicsWorld – amino acid detected in space
Artist’s impression of an environment in which the experimenters wanted to create glycine.
Photo credit: Professor Harold Linnartz