Evolutionary history of ATP

I’ve recently been trying to learn some of the fundamentals of biochemistry (especially of phosphate bond energy) and I’ve run across something in my studies. Adenosine Triphosphate, the primary energy currency of life, seems ideal for its role (it has medium energy as far as organophosphorus bonds are concerned, triphosphate bond increases Gibbs energy, among others). Here’s my questions: What was the first use of ATP in life? Was it in metabolism or as a nucleic acid construction molecule?I ask this question primarily due to my unfamiliarity with biochemistry literature, in the hopes that someone who has studied biochemistry extensively will say, Oh that’s easy. We were told in class So far in my research this does not seem to be the case (and my online googling brings up a bunch of creationist nonsense- like Trueorigin).From my investigation so far, and using a bit of logic, I think that ATP was first used as a nucleic acid construction molecule. Why? A few reasons:1) It’s complex. It has a sugar (fairly oxidized organic compound) bound to an adenine (reduced H-C-N molecule) with a triphosphate attached to the sugar. These three separate molecules likely form in different environments. If ATP had an ancient, metabolism first origin, it would be very hard to prebiotically synthesize. However, if it was used as a nucleic acid building block first, then this problem would be part of the whole how did the RNA world first develop which more researchers are working on.2) It has properties specifically selected for as a nucleic acid building block. First and foremost, the stereochemistry of ribose is specified for the formation of long nucleic acid chains. The stereochemistry of ribose is not utilized to this extent in metabolism. Also, ATP is used to build nucleic acid via the reaction:
ATP + NA --> A-NA + PPi
where PPi is pyrophosphate, P2O74-.
Release of pyrophosphate is an energetically favorable reaction as pyrophosphate is a rare component of cellular systems. Typically ATP in metabolism releases energy via loss of a phosphate bond:
ATP --> ADP + Pi
where Pi is orthophosphate. This reaction is much more dependent on product concentrations than the prior reaction, as orthophosphate is much more abundant than pyrophosphate.So in my opinion, ATP was first used as a building block for RNA, but due to its energetic versatility, it was coopted into metabolism. This does establish some history for life’s early evolution:RNA-dominated replication
Followed by
ATP as energy currency
Followed by
DNA-dominated replicationThoughts? Comments?

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