If there's one thing that most folks will remember from even just high school biology class, it's that the mitochondria is the "powerhouse of the cell." Why? Because it creates ATP, a cellular chemical that gives every life form on Earth, humans included, their energy.
But while humans have been aware of ATP for quite some time, how it actually ascended to metabolic dominance has remained mysterious. Its universality suggests that it's been around since the very dawn of life, but its complexity — and therefore the energy it takes to actually create it — makes that unlikely. As such, scientists have been puzzling over the question for quite some time.
Until, perhaps, now.
In a new study published in the journal PLOS Biology, a team of researchers at University College London posit that it became the "universal currency of life" by way of a little thing known as phosphorylation.
Basically, phosphorylation is the process by which ATP is created. A phosphate molecule is added to another chemical called ADP, and voíla: ATP is born. That same phosphate, as ScienceAlert explains, is then used for another process called hydrolysis, or the reaction of an organic chemical with water that breaks down ATP for use — and that connection with water may be where the secret to ATP's metabolic dominance lies.
Well, partly. As the scientists discovered in their research, ATP couldn't rise to the top alone. It needed both water and another phosphorylating molecule, called AcP, to do it. And in fact, it's likely that ATP actually knocked out AcP as top energy-giving dog.
AcP is a cellular chemical that single-celled organisms like bacteria and archea still use for their own metabolic processes. Because AcP is so centric to these very early-forming microbial life forms, it's also believed to be one of the earliest cellular chemicals.
In the research, the scientists discovered that when added specifically to water rich in iron ions— which would have been present in early Earth's freshwater as a result of volcanic eruptions — AcP can phosphorylate ADP to ATP.
In other words? AcP was likely here first, and under the right conditions, phosphorylation — and thus ATP — became possible. And with the production of the more complex particle that is ATP, more complex life forms (like us!) eventually became possible.
"It was very surprising to discover the reaction is so selective — in the metal ion, phosphate donor, and substrate — with molecules that life still uses," study coauthor and biochemist Silvana Pinna said in a statement. "The fact that this happens best in water under mild, life-compatible conditions is really quite significant for the origin of life."
"Over time, with the emergence of suitable catalysts, ATP could eventually displace AcP as a ubiquitous phosphate donor," added coauthor and biochemist Nick Lane, "and promote the polymerization of amino acids and nucleotides to form RNA, DNA, and proteins."
While the findings aren't entirely definitive, they are exciting. Humans have been wondering where we — and, well, everything — came from for quite some time. This research, if anything, provides a fascinating new clue.
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