How did the building blocks of life come together to spawn the first organisms? It's one of the most longstanding questions in biology — and scientists just got a major clue.
In a new study published in the journal Nature, a team of biologists say they've demonstrated how RNA molecules and amino acids could combine, by purely random interactions, to form proteins — the tireless molecules that are essential for carrying out nearly all of a cell's functions.
Proteins don't replicate themselves but are created inside a cell's complex molecular machine called a ribosome, based on instructions carried by RNA. That leads to a chicken-and-egg problem: cells wouldn't exist without proteins, but proteins are created inside cells. Now we've gotten a glimpse at how proteins could form before these biological factories existed, snapping a major puzzle piece into place.
"We have achieved the first part of that complex process, using very simple chemistry in water at neutral pH to link amino acids to RNA," said study coauthor Matthew Powner, a chemist at University College London, in a statement about the work. "The chemistry is spontaneous, selective, and could have occurred on early Earth."
The results, he added, show how "RNA might have first come to control protein synthesis."
Amino acids have been around far longer than life has on our planet. We've even found amino acids — plus all the five major ingredients of DNA and RNA called nucleotides — on asteroid samples plucked directly from outer space.
The curious thing about amino acids, though, is that they don't easily link together; something has to kickstart the chemistry that allows life as we know it.
To find out what that might be, the researchers focused on a reactive molecule called pantetheine, which is already known for its crucial role in metabolism. In a previous study, the researchers found that these compounds were likely abundant in lakes on early Earth.
When they threw together a watery stew of pantetheine and amino acids, the team found that the amino acids reacted with the compound to create another chemical called aminoacyl-thiol. This thiol, they further demonstrated, combined with free-floating RNA in water at a neutral pH to start a reaction that transferred the amino acids to the RNA, linking them together.
"In a scenario where you have amino acids, where you have RNA molecules, if you have thiols — sulfur molecules — this is, I think, almost inevitable that this kind of process can happen," Powner told the Washington Post.
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