Peptides on Stardust could provide a shortcut to life

Billions of years Previously, some unknown location on the sterile primordial Earth became a cauldron of complex organic molecules from which the first cells emerged. Origins of life researchers have proposed countless imaginative ideas about how that happened and where the necessary raw materials came from. Some of the hardest to identify are proteins, an important backbone of cell chemistry, because in nature today they are made exclusively by living cells. How did the first protein form without life to make it?

Scientists are mainly looking for clues on Earth. However, a new discovery suggests that the answer may be found beyond the sky, within the dark interstellar clouds.

Last month in Natural Astronomy, a team of astrophysicists has shown that peptides, the molecular subunits of proteins, can form spontaneously on solid, frozen cosmic dust particles drifting across the universe. In theory, those peptides could have traveled inside comets and meteorites to the young Earth – and to other worlds – to become some of the starting materials for life.

According to Serge Krasnokutski, lead author of the new paper and a researcher at the Max Planck Institute for Astronomy and Friedrich Schiller University in Germany. And that simplicity “suggests that proteins were among the first molecules involved in the evolutionary process that led to life,” he said.

Whether those peptides can survive the arduous trip from space and contribute meaningfully to the origin of life is an open question. Paul Falkowskia professor in the School of Environmental and Biological Sciences at Rutgers University, says the chemistry demonstrated in the new paper is “great” but “hasn’t bridged the extraordinary gap between prebiotic and biotic chemistry. first evidence of life.” He added, “There is a spark that is still missing.”

However, the discovery by Krasnokutski and his colleagues suggests that the peptide may be a much more readily available resource in the universe than scientists had believed, a possibility that could also have consequences for the universe. prospects for life elsewhere.

Cosmic dust in a vacuum

Cells make protein production look easy. They produce both peptides and proteins lavishly, aided by an environment rich in useful molecules such as amino acids and their own stockpile of genetic instructions and catalytic enzymes (which themselves usually proteins).

But before the cell existed, there was no easy way to do it on Earth, Krasnokutski said. Without any enzymes that biochemistry provides, peptide production is an inefficient two-step process that involves first generating amino acids and then removing water as the amino acids link into chains. in a process known as polymerization. Both steps have a high energy barrier, so they only occur when large amounts of energy are available to help start the reaction.

Because of these claims, most theories of the origin of proteins have focused on extreme environmental scenarios, such as near hydrothermal vents on the ocean floor or assuming the presence of molecules like RNA with catalytic properties that can lower the energy barrier enough to push reactions forward. (The most common origin theory of life suggests that RNA precedes all other molecules, including proteins.) And even in those cases, Krasnokutski says, “special conditions” are required. to concentrate enough amino acids for polymerization. Although many suggestions have been made, it is not clear how and where such conditions might have arisen on the primordial Earth.

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