(10-27-2016, 04:51 PM)Avalancheon Wrote: Hi everyone, I'm new to the forum here. I just signed up today, even though I've been reading orions arm for several years. One topic that raised my interest was about the nature of alien biochemistry. Specifically, about organisms that rely on carbon for structure, and water as a solvent. (These are called type 1 life forms in the OA page) Is it inevitable that carbon based life would use DNA and/or RNA to encode genetic information? Are other arrangements possible, or even likely?
A related question: Are there any type 1 biospheres in the OA universe that use something other than DNA? Or that maybe use DNA with different nucleotides, something other than A-G-C-T? I'm trying to learn more about this and am grateful for any answers.
Hi, biochemist and carbon chauvinist here. It's certainly possible for DNA life to use other nitrogenous bases. In the field of synthetic biology, "hachimojo DNA" has been created, with four additional bases. In our DNA we have the A=T and C≡G pairs, but hachimojo DNA can also have P≡Z and B≡S pairs. Check its Wikipedia article for more sources and the structure of these molecules. In sum, the hachimojo system works for both DNA and RNA, which can be transcribed (but not translated, as the researches didn't create a suitable genetic code) and even showed ribozyme activity.
However, I'd bet that some nitrogenous bases are very common even in extraterrestrial life, due to the easiness of their synthesis. For example, take adenine. Its chemical formula is C₅H₅N₅, which is a pentamer of hydrogen cyanide (HCN). Syntheses mimicking primitive Earth-like conditions have been known since the 1960s.
I think that life isn't necessarily made of the best molecules possible, but the ones that were most available during the prebiotic Earth.
In the hachimojo example, consider how base Z has a nitro group, a functional group that is extremely rare in living organisms (in fact, I don't recall seeing it in any biological compound during my undergraduate years). Even if this base provided a superior form of biochemistry, it simply wouldn't have come around because its natural synthesis is very unlikely.
Anyhow, OA does have an example of an (arguably) naturally occurring expanded nucleic acid life, on Baryos:
Quote:Life on Baryos is not very exotic, being based on left-handed amino acids, a nucleic acid using six nucleotides, and with starches doing many functions performed by proteins in terrestrial life.
Take also a look to the abiogenesis article, to know more about the "lore" of abiogenesis in OA. It does mention explicitly which nucleic acids are known to have been found on primitive worlds:
Quote:Examples of this Nucleic Acid world stage are widespread, and molecules such as RNA, PNA, TNA and even DNA are found in simple cells known as protobionts, often associated with the previously mentioned PAH compounds.
Strangely though, I couldn't find any mentions of what OA's most popular xenosophonts (like to'ul'hs and muuh) use as their genetic material. The to'ul'h however could be DNA-based, as we already know of examples of hyperthermophile life on Earth.