Scientists discover chemical reactions that explain how life began on Earth
Using what they know about the chemistry of the early Earth, scientists have found a new chain of chemical reactions that could have produced the biological building blocks of Earth over all those eons.
It is known that the Earth was, at first, so young and new, that there was no sign of life on it. Then, somewhere, somehow, something strange happened in chemistry, and the molecular building blocks of our first unicellular ancestors emerged: amino acids and nucleic acids that came together in just the right way to continue the chain reaction that gave rise to life.
We are not entirely sure about the details of this appearance, which occurred billions of years ago, especially since it did not leave any trace in the fossil record, but recent scientific discoveries reveal some of this mystery.
Chemist Ramanarayanan Krishnamurthy said; From the Scripps Research Institute, "We have come up with a new model to explain this transition from prebiotics to biochemistry," adding, "We believe that the type of reactions we describe are likely what would have occurred in early Earth."
Scientists are taking what they know about current biological processes and trying to recreate them in laboratory environments using the chemistry of the early Earth, 3.7 billion years ago.
Evidence suggests that one of the molecules found was cyanide, which may have been useful in the emergence of life on Earth.
The role of cyanide in this process has been explored by a number of research teams around the world. Earlier this year, Krishnamurthy and colleagues demonstrated how cyanide can readily produce basic organic molecules at room temperature and across a wide range of pH conditions. And with some added carbon dioxide, this reaction really speeds up.
This prompted the researchers to wonder if they could replicate their success in trying to create more complex organic molecules from the amino acids that make up all proteins in living cells?
The precursors of amino acids, today, are called alpha-keto acids, which react with nitrogen and enzymes to produce amino acids.
Although alpha-keto acids may have been present on Earth early on, the enzymes were not; Which led the scientists to conclude that the amino acids must have been formed from precursors called aldehydes instead. Which raises, of course, a host of other questions.
Krishnamurthy and colleagues think there may be a pathway by which alpha-keto acids can synthesize amino acids without the enzymes present. And they started the experiments with alpha-keto acids, of course, and the addition of cyanide; Their previous experiments showed that it is an effective engine for chemical reactions that produce organic molecules.
Ammonia, a compound of nitrogen and hydrogen also found in the Earth from early on, was added after that; To contribute to the production of required nitrogen.
It took a little trial and error to figure out the last bit, but just as the researchers found in their previous work, it ended up producing carbon dioxide.
“We were expecting it to be very difficult to figure out, and it turned out to be simpler than we had imagined,” Krishnamurthy said. “If you just mix keto acid, cyanide and ammonia, it's still there. But once you add carbon dioxide, even in small amounts, the reaction will speed up.”
The team's overall results indicate that carbon dioxide was a vital component of the emergence of life on Earth, but a requirement that it be combined with other components.
The team also discovered that a byproduct of their reactions is a molecule similar to a compound produced in living cells called orotate. This is one of the basic building blocks of nucleic acids, including DNA and RNA.
The team's results are very similar to the interactions that occur in living cells today. Which means that the result will eliminate the need to explain why cells switch from aldehydes to alpha-keto acids; So the team believes that their discovery represents a more likely scenario for the emergence of prebiotic molecules than the aldehyde hypothesis.
The next step is to conduct more experiments with this chemical compound. To discover other prebiotic molecules that may appear during the experiment.
In turn, this will help establish the plausibility or implausibility of the various scenarios that describe the humble beginnings of all life on Earth.
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