Like everyone else, I'm not quite sure what you're asking, but I'll post a couple of paragraphs from Life Ascending which might address your question. RNA WORLD: RNA --> DNA
And so Martin and Koonin envisaged populations of cooperative RNAs emerging in mineral cells, each RNA encoding a handful of related genes. The drawback to this arrangement, of course, is that the RNA populations would be vulnerable to remixing into different, possibly ill-suited, combinations. A cell that managed to hold its 'genome' together, by converting a group of cooperative RNAs into a single DNA molecule, would retain all its advantages. Its replication would then be similar to a retrovirus, its DNA transcribed into a swarm of RNAs that infect adjacent cells, bestowing on them the same ability to deposit information back into a DNA bank. Each new flurry of RNAs would be freshly minted from the bank, and so less likely to be riddled with errors.
How hard would it have been for mineral cells to 'invent' DNA in these circumstances? Not so hard, probably; much easier, in fact, than inventing a whole system for replicating DNA (rather than RNA). There are just two tiny chemical differences between RNA and DNA, but together they make an immense structural difference: the difference between coiled catalytic molecules of RNA, and the iconic double helix of DNA... Both of these tiny changes would be hard to stop taking place virtually spontaneously in vents. The first is the removal of a single oxygen atom from RNA (ribonucleic acid) to give deoxy-ribonucleic acid, or DNA. The mechanism today still involves involves the kind of reactive (technically free-radical) intermediates found in vents. The second difference is the addition of a 'methyl' group on to the letter uracil, to give thymine. Again, methyl groups are reactive free-radical splinters of methane gas, plentiful in alkaline vents.
So making DNA could have been relatively easy: it would have formed as 'spontaneously' in the vents as RNA (I mean its formation from simple precursors would have been catalysed by minerals, nucleotides, amino acids, and so on). A slightly more difficult trick would have been to retain the coded message, which is to say, to make an exact copy of the sequence of letters in RNA in the form of DNA. Yet here too the void is not insuperable. To convert RNA to DNA requires just one enzyme: a reverse transcriptase, held in trust by retroviruses like HIV today...