I study quite a lot of chemistry, biology, and other branches of those fields, alongside some forms of astronomy. As part of a large-scale project I have been working on for a few years and continue to do so, aiming to be as scientifically accurate as I can get that involves extraterrestrial lifeforms.
I have questioned whether or not it is possible for DNA and RNA to have completely different substitutes. Both compose of a sugar and phosphate backbone with a base, but I wondered if completely different molecules could take their place, functioning with at least a similar role of storing genetic information among native organisms on the planet. I am aware of a group of synthetically-made nucleic acids known as XNA exists, most of which containing a differing sugar backbone, but still retaining many of the structural components of DNA. Although there is room for variation among these (such as different bases, and a different amount of bases) I want to consider the possibility of a completely different composition altogether.
I figure it may be possible in the first place considering the differing chemical compositions in other planets' biospheres that may affect what concentrations of certain molecules are available. Whatever biomolecule in their place has to be ubiquitous, stack to create polymers, bond in certain ways and be replicatable in general, which it may be tricky to find another one that isn't the ones found in nucleic acids as we know them.
Both alternatives of the structure still using macromolecules we know, such as lipids, proteins and the sort, and the possible more theoretical ones of not using these at all are both what I'm open to. Any sort of other-worldly method genetic information could be stored, in a possibly scientifically accurate way, is mostly the topic at hand that I wish to find any answers on.
Is it possible? What could they be, if so, if that could even be answered? How specific they could be on their functions and make-up does not matter; the concept, if it could theoretically work, is what matters.