Scientists have achieved a major breakthrough toward unraveling the mystery of how life first arose on Earth and whether it might exist elsewhere in the universe, reports a new study.
A longstanding mystery–perhaps the mystery, existentially speaking–is how life originated from non-living, or abiotic, chemicals. Researchers at Purdue University discovered that peptides (strings of amino acids which form the building blocks of all life) can spontaneously form when droplets of water react with the atmosphere. This is a result of rapid reactions such as when water hits rocks and creates a misty spray. This could occur in conditions similar to those that existed on Earth some four billion years ago, when life first took hold on our planet.
The discovery provides “a plausible route for the formation of the first biopolymers,” which are complex structures produced by living organisms, according to a study published on Monday in the Proceedings of the National Academy of Sciences. The team says the discovery could even speed up the development of novel drugs and medical treatments by providing a new medium for fostering rapid chemical reactions.
” Although there are many studies that show peptide formation, they use modified amino acids or catalysts to create species unnaturally.” R. Graham Cooks is the Henry B. Hass Distinguished professor of Analytical Chemistry at Purdue. He was the senior author of this study and also serves as the Henry B. Hass Distinguished professor of Analytical Chemistry.
Cooks has now demonstrated that peptides can form in chemical systems similar to those that were present on Earth’s ancient surface, including seawater from the primordial oceans of our planet or freshwater that drips down hillsides.
“The most interesting implication is that similar chemistry explains other essential biological polymers, not just peptides,” he noted, adding that his team plans to publish more on this topic soon.
In other words, this study provides a glimpse into how nonliving substances were assembled into living organisms in the early days of our planet’s history. This is known as biogenesis. The formation of peptides is an important step in abiogenesis because these structures form the basis of biomolecules such as proteins, which can perform the self-replicating mechanisms that are necessary for life.
The team was able to reconstruct the possible formation of these peptides by running “droplet fusion” experiments that simulate how water droplets collide in the air, which Cooks described as “like two kids with garden hoses spraying each other.”
These experiments show that the surface of the droplets, where water meets air, is a region that can be exceptionally productive at spinning peptides out of the types of amino acids that have been delivered to Earth by meteorites for billions of years. As a result, the experiments offer a possible solution to what’s known as the “water paradox,” a problem that has puzzled scientists in the abiogenesis field for years.
“The water paradox is the contradiction between (i) the very considerable evidence that the chemical reactions leading to life occurred in the prebiotic ocean and (ii) the thermodynamic constraint against exactly these (water loss) reactions occurring in water,” Cooks explained. “Proteins are formed from amino acids by loss of water” and “loss of water in water will not occur because the process will be reversed by the water (thermodynamically forbidden).”
Put another way, peptides need some level of dehydration to form, but that is very hard to accomplish in a hydrated environment like a water droplet. Cooks and colleagues have demonstrated that microdroplets possess unique properties, such as an increased reactivity at the surfaces. This has been known for more than 10 years. This air-water interface is like an oasis in the watery droplet’s world. It allows for the necessary loss-of-water reaction to make peptides from amino acids.
“Expressing this colloquially, we claim that the surfaces of water microdroplets are not wet, they are dry,” Cooks said. “So the water paradox is broken.”
The discovery has implications off of Earth as well. This study indicates that ancient Earth’s sea spray drops may have been the result of peptide factories, which enriched their environments with essential ingredients. The same processes may be common on other planets with similar conditions, which is useful information as scientists continue to search for life in our own solar system, and beyond it.
Indeed, Cooks said that the results “reinforce the NASA mantra ‘follow the water,'” referring to the priority that researchers searching for aliens give to planets that might host liquid water. Based on his findings and the possibility of sea spray being a major driver for peptide formation, Cooks suggested an additional mantra: “Seek rough oceans.”
In addition to revealing insights about the exotic embers of life in the deep past, the study also has practical medical applications for the present and near future.
” Droplet-accelerated reactions are a broad field of application, with some applications only beginning to emerge in drug discovery,” Cooks stated. “Because reactions are so fast they can be performed automatically, on a small scale, to make drug candidates and then tested for biological activity, still automatically in high throughput fashion. We have built instrumentation to do this.”
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