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Here’s what you’ll learn when you read this story:
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In the beginning, there were prebiotic compounds that were the ingredients for life but had not yet come together in the right ways.
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Organic sulfur compounds known as thioesters might have catalyzed reactions that ultimately led to the formation of life.
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An experiment that used a thioester to spontaneously catalyze the binding of RNA to amino acids may be telling us what happened billions of years ago.
Primordial Earth would have seemed like an alien planet to human eyes. When the first known life emerged about 3.7 billion years ago, the planet’s crust had just solidified beneath an endless ocean. These life-forms were prokaryotes, single-celled organisms without a nucleus, such as bacteria and archaea. They would leave evidence of their existence in fossilized stromatolites or fossil carbon embedded in rocks. The other thing they left behind was an enduring mystery.
How life spawned on Earth remains unknown. Whether they were already here or brought by comet and asteroid collisions, the essential life components of carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur somehow ended up on the young planet. They combined and recombined with each other and certain metals. Somehow, chemical reactions in those antediluvian waters resulted in prebiotic molecules such as proteins, lipids, amino acids, and other components of the nucleic acids RNA and and DNA. Early genetic systems came into being. Primitive forms of life replicated themselves and separated from their surroundings.
Because rewinding billions of years is not an option, chemist Matthew Powner of University College London has found a way to demonstrate how life possibly arose on Earth.
“Understanding how nucleotide-controlled peptide biosynthesis could have first emerged is a notable gap in our understanding of life but is a formidable challenge owing to the immense complexity and antiquity of protein synthesis,” Powner said in a study recently published in Nature. “However, all proteins are built [the same way.]”
Powner had previously shown how peptides, which are made of amino acids and merge to create proteins, could form out of substances such as hydrogen sulfide and ferricyanide. He and his team of researchers figured out how to make RNA spontaneously bind to amino acids in water that is neither acidic nor alkaline, supposedly like the waters of early Earth. The reaction was powered by the energy of organic sulfur compounds known as thioesters.
What Powner’s team managed to pull off showed a convergence of two theories hypothesizing about what happened at the dawn of life. The “thioester world” theory suggests that thioesters were catalysts, triggering and speeding up reactions that gave rise to early metabolic processes. The “RNA world” theory posits that RNA appeared before DNA. It is thought that, in the first single-celled organisms, molecules preceding RNA managed structure, catalyzed reactions and functioned as a primitive sort of genetic code until RNA was synthesized from some of these molecules and took over.
It is possible that thioesters could have been involved in the reactions that eventually brought about RNA. Life would not be life without it. DNA carries information on how to synthesize proteins such as antibodies, collagen, and hemoglobin, while RNA transmits that information to ribosomes, which make those proteins from 20 different amino acids through ribosomal peptide synthesis or RPS. This process is usually initiated by the amino acid methionine, which (among other functions) regulates metabolic processes. Powner plans to continue probing the origins of RPS, relics from the distant past, in the near future.
“What is particularly groundbreaking is that the activated amino acid used in this study is a thioester, a type of molecule made from Coenzyme A, a chemical found in all living cells,” he said in a recent press release. “This discovery could potentially link metabolism, the genetic code and protein building.”
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