Theoretical origin of life: simple peptides are out there (Introduction)

by David Turell , Tuesday, March 08, 2022, 22:52 (991 days ago) @ David Turell

And as usual we are starting to know how life appeared naturally; Not!:

https://www.quantamagazine.org/peptides-on-stardust-may-have-provided-a-shortcut-to-lif...

"Last month in Nature Astronomy, a group of astrobiologists showed that peptides, the molecular subunits of proteins, can spontaneously form on the solid, frozen particles of cosmic dust drifting through the universe. Those peptides could in theory have traveled inside comets and meteorites to the young Earth — and to other worlds — to become some of the starting materials for life.

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{"Whether those peptides could have survived their arduous trek from space and contributed meaningfully to the origin of life is very much an open question. Paul Falkowski, a professor at the School of Environmental and Biological Sciences at Rutgers University, said that the chemistry demonstrated in the new paper is “very cool” but “doesn’t yet bridge the phenomenal gap between proto-prebiotic chemistry and the first evidence of life.” He added, “There’s a spark that’s still missing.”

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"But before cells existed, there wasn’t an easy way to do it on Earth, Krasnokutski said. Without any of the enzymes that biochemistry provides, the production of peptides is an inefficient two-step process that involves first making amino acids and then removing water as the amino acids link up into chains in a process called polymerization. Both steps have a high energy barrier, so they occur only if large amounts of energy are available to help kick-start the reaction.

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"In their new paper, Krasnokutski and his colleagues showed that these reactions in the gas clouds would likely lead to the condensation of carbon onto cosmic dust particles and the formation of small molecules called aminoketenes. These aminoketenes would spontaneously link up to form a very simple peptide called polyglycine. By skipping the formation of amino acids, reactions could proceed spontaneously, without needing energy from the environment.

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"The researchers hypothesized that billions of years ago, as cosmic dust stuck together and formed asteroids and comets, simple peptides on the dust could have hitchhiked to Earth in meteorites and other impactors. They might have done the same on countless other worlds, too.

"The delivery of peptides to Earth and other planets “certainly would provide a head start” to forming life, said Daniel Glavin, an astrobiologist at NASA’s Goddard Space Flight Center. But “I think there’s a large jump to go from interstellar ice dust chemistry to life on Earth.”

"First the peptides would have to endure the perils of their journey through the universe, from radiation to water exposure inside asteroids, both of which can fragment the molecules. Then they’d have to survive the impact of hitting a planet. And even if they made it through all that, they would still have to go through a lot of chemical evolution to get large enough to fold into proteins that are useful for biological chemistry, Glavin said.

"Is there evidence that this has happened? Astrobiologists have discovered many small molecules including amino acids inside meteorites, and one study from 2002 discovered that two meteorites held extremely small, simple peptides made from two amino acids. But researchers have yet to discover other convincing evidence for the presence of such peptides and proteins in meteorites or samples returned from asteroids or comets, Glavin said. It’s unclear if the nearly total absence of even relatively small peptides in space rocks means that they don’t exist or if we just haven’t detected them yet.

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"The researchers are now planning to test whether bigger peptides or different types of peptides can form in molecular clouds. Other chemicals and energetic photons in the interstellar medium might be able to trigger the formation of larger and more complex molecules, Krasnokutski said. Through their unique laboratory window into molecular clouds, they hope to witness peptides getting longer and longer, and one day folding, like natural origami, into beautiful proteins that burst with potential." (my bold)

Comment: note the bold, lots of grant money based on hope, while ignoring the obvious massive problems pointed out with great reason by James Tour.