This question is tied to the “Glass Trees” question I asked earlier which everyone seemed to like. Since y’all had such good opinions on that, I figured I’d bring this particular quandary to y’all in hopes that you could bring peace to my nearly month-long torment over what to do.
The setting: A planet 90% the mass of Earth, with an iron core to provide a magnetosphere. Planet has similar composition to Earth, though has a moon which causes tides roughly 2.5x greater. (Orbital mechanics aren’t important here, this is just to describe the setting.) Life forms are carbon-based, using sugar-phosphate based genetic biopolymers. Atmosphere is mostly comparable with that of early Earth, during the Ediacaran/Cambrian.
The Setup: So I wanted to have a genetic compound used for the biosphere that was different from Earth, but not so different that it would be incomprehensible. My main needs for this mirror to DNA were:
- It should be comprised of the same or similar core elements as DNA; no swapping Carbon with Silicon here, we stayin’ organic on this planet.
- It should be unable to interact with DNA or RNA. I want to try avoiding any possibility of “this alien virus could infect you and mutate you into a monster”, or any cross-species breeding going on. Terran life and these aliens should not be able to interact on a genetic level, ideally.
- It should function in roughly equivalent ways - self-replicating, coding for proteins, allows for Darwinian evolution, all that bacon.
The Problem: …I am not good with chemistry. I’m skilled with biology & geology, I’m a passionate amateur for astronomy, and I know enough physics (quantum & otherwise) to follow a conversation. But I have always struggled understanding chemistry in all its forms; without a smart person to balance me out, I’m stumbling in the dark. That being said, I did try to do some research, and even though I only understand 50%-70% of it, I at least have enough to make inferences.
My Research: My first candidate was HomoDNA, an alternative form of DNA that replaces Deoxyribose with Dideoxyallopyranosyl, which is a homolog hexose. I operated for a while under the assumption that this HomoDNA would work similarly enough to DNA & RNA to be comparable. However, thanks to a paper that a friend of mine sent me, I now know that HomoDNA doesn’t form stable Watson-Crick pairings like DNA & RNA does. Plus, it doesn’t seem to form stable helical frames either. So Homo-DNA is out.
D-pyranosylribose (p-RNA), the pentapyranosyl isomer of RNA (whatever that means), has shown to form pairing comparable & superior to DNA & RNA. It also does not bond with standard DNA & RNA, which makes it more viable for my "aliens cannot infect Earthlings" criteria. I don’t know much about it besides the small reference in that fore-mentioned paper.
Among synthetic or Xeno-nucleic acids (XNA's), Fluoro-arabinose (FANA) and Anhydrohexitol (HNA) are also favored alternatives to DNA. They form stable base pairing, can also pair with DNA, and also work with synthetic catalytic enzymes, which is prevalent to the idea of the chemical origins of life. However, I don’t know how difficult these synthetic strains would be to form under natural circumstances; I recall that something mentioned regarding Hajimoji-DNA is that it cannot exist outside of a lab environment, so they must introduce something that allows it to form and prosper that doesn’t exist in nature.
And for the record, I did look into Hajimoji-DNA. I am likewise intrigued, though I feel as if having a structure that codes for 8 different nucleotides would lead to a higher risk of mutation & cancers, as well as having more potential to code various proteins. It feels like an impractical thing for nature, in that regard.
My Question: (finally) My question that I present to you all is, which of these DNA alternatives seems to be the most likely one to arise naturally on an alien planet? Which of them would fit the criteria I listed above best? Is there another substitute that you feel fits better? Any advice and information you could provide would be helpful! (Just keep in mind, I’m no chemist, so y’all might need to dumb a few things down for me.) :P
ADDEN.: RESPONSE TO GNA SUGGESTION I did some research into Glyco-Nucleic Acids (GNA), as folks in the comments suggested; I did confirm, the structure is the same, just the paper calls it “glycerol” instead of “glycol”. This also seems promising, but there is some confusion over how stable it is. The research paper “De Novo Nucleic Acids” cites GNA as having a lower melting temp., thus forming a more flexible backbone structure and destabilizing Watson-Crick pairing. However, the Wikipedia article linked says the exact opposite: that GNA requires a higher melting temperature, and thus forms more stable Watson-Crick pairing. I’m unsure if this is an error on someone’s end (as in whoever’s writing the paper/articles), or perhaps Glyco-Nucleic Acids and Glycero-Nucleic Acids ARE different? Hope y’all can help.