Origin of life: A prebiotic route to DNA

Comments?

Will need to read the actual publication but it’s behind a paywall, and the pop-sci article is too sparse on details.

I really don’t like what I’m reading in the abstract which makes a number of rather grandiose declarations I have a hard time seeing how a couple of chemistry experiments alone can support. I’ve highlighted what I see as the offenders standing out the most to me.

Abstract

It is assumed that RNA played a key role in the origin of life. The hypothesis of the RNA world is that the transition to more complex but more stable DNA for continuous information storage and replication requires the development of a ribonucleotide reductase to obtain the deoxyribonucleotides from ribonucleotides. This step, as well as an alternative path from abiotic molecules to DNA‐based life, is completely unknown. Here we show that deoxyribonucleosides are formed under relevant prebiotic conditions in water in high regio‐ and stereoselectivity from all canonical purine and pyrimidine bases by condensation with acetaldehyde and sugar‐forming precursors, e.g. formaldehyde, glycolaldehyde and glyceraldehyde. We can explain the origin and selection of deoxyribose versus other deoxysugars during nucleoside formation. Thus, we have found a continuous path to DNA nucleosides, starting from simple, prebiotically available molecules. Furthermore, we identified the deoxyapionucleosides (DApiNA) as a further potential DNA progenitor. Our results allow to conclude that the DNA world evolved much earlier than previously assumed.

I’d like to know how they know that the conditions they performed their experiments under are “relevant”? Or even what that means. Relevant to what? The results might be interesting, and they might be relevant to the process by which life originated. But we can’t know that from an experiment like this alone.

The last one is just absurd. No, performing an experiment, even supposing the conditions used were likely to obtain somewhere on the early Earth, where DNA nucleosides are produced allows no conclusion about when DNA actually evolved. Even if conditions like this experiment did obtain somewhere on Earth once upon a time, and even if DNA nucleosides were produced in similar yields back then under those conditions, it still says nothing about whether that is in fact how life originated or that this is how DNA evolved. These are still complete unknowns.

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By “relevant prebiotic relevant conditions” they just mean conditions that are plausible for the prebiotic world. I’m no chemist, but their experiments seem simple enough to qualify.
Summary:
Nucleobases + acetaldehyde = vinyl nucleobases
Vinyl nucleobases + formaldehyde or D-glyceraldehyde = deoxyribonucleosides

These reactions took place over several days in sealed vials of water at 50C.

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