New research suggests life began with a chimeric mix of RNA and DNA.
This would explain a longstanding puzzle, because pure RNA is hard to split apart.
Enzyme-free RNA transmission could have implications for medicine like vaccines.
In 2020, ribonucleic acid (RNA) has been in the news because of a special kind that has enabled the first two COVID-19 vaccines. But in new research, scientists suggest RNA’s origins and role in the formation of life could have been very different than previously believed—and sharing the spotlight with deoxyribonucleic acid (DNA).
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The missing piece of the explanation is a molecule called diamidophosphate (DAP), which “could have chemically knitted together tiny DNA building blocks called deoxynucleosides into strands of primordial DNA,” Scripps Research explains in a statement.
Then, researchers believe, DAP mixed in quantities that turned out the first DNA and RNA. This means the first life forms that could reproduce and transmit genetic material were likely a mix of both kinds, not just RNA.
Here’s the problem with the RNA-only model (also known as the "RNA world hypothesis"), stated at its most succinct: RNA is too “sticky.”
That means that, like hydrogen for example, RNA bonds and will not detach from other molecules. In evolutionarily modern times, we know RNA is split from its fresh copies by enzymes, but enzymes arose after RNA. How did the first RNA strands come unstuck without help?
One potential answer: chimeric molecules. Today, it’s possible—although vanishingly rare—for humans to be chimeric, meaning they have more than one set of DNA. This is a favorite mechanism for crime TV shows, but only about 100 cases have ever been documented.
For primordial molecular strands of DNA and RNA, chimerism takes the form of single strands with evidence of both kinds of genetic information. That means reducing the “stickiness” of RNA alone and creating a path that explains original RNA replication without enzymes. It’s like those popsicles with two sticks: holding the sticks gives you leverage to snap apart the double popsicle.
Understanding how life began is a worthy end unto itself, but there’s a valuable series of ramifications from this research. First, it gives other researchers more experimental evidence to study as they do follow-up studies, helping the entire field to home in on the likeliest explanation for how life began.
And second, if RNA managed to unstick itself without enzyme help, that could have implications for the same mRNA that’s in the news in 2020. Enzymes are fragile, researchers say, meaning that in any given supply chain that results in mRNA for consumption, the enzymes are often the weakest link.
Scientists may be able to model future RNA synthesis on an original, chimeric process that doesn’t require enzymes at all. With fewer moving parts and less vulnerability, that could mean more robust products that can travel further, last longer, and endure a wider variety of conditions—even vaccines.
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