Is DNA universal

[Bez]

I ask this more out of personal interest rather than it having any impact on game mechanics.

The question is whether the self-replicating macro-molecules that are universal in all life on Earth (DNA/RNA) are also present on other worlds?
Obviously, worlds which were seeded by The Ancients will have species that have DNA or RNA, but what about other worlds, with completely alien species present?

If DNA is universal, what differs on other worlds? Are there different base-pairs, or different proteins used, and how do they impact interactions with DNA-based life from Earth?
If DNA is limited to species which originated on Earth, then what does genetic material look like on other worlds, and does it cause problems for DNA-based life?

We take it for granted that if a world is breathable and has a comfortable gravity, then we can settle there and all is fine.
However, all it would take would be for someone to walk on such a planet to potentially contaminate the world irreparably.
There are also considerations around whether humans could grow things, eat local plants and animals or even exist without being lethally infected with an alien virus that has adapted itself to interact with DNA. Viruses adapt far quicker than humans, and can reproduce, mutate and adapt at an incredible rate.

 

[Reynard]

The Na'vi of Pandora don't use DNA according to the references.

MgT 2300AD - Tools for Frontier Living gives rules that determines biological compatibility on other worlds including cell biochemistry.

 

[Bez]

Cool - I will check out that resource.

Depending on the campaign tone, most referees would probably hand-wave such things rather than getting bogged down in the biochemistry of each and every world. It's far too mundane a topic and can't compete with starship battles or exploring alien ruins.

It would be interesting to hear from a referee who does insist on understanding biochemical interactions though, but I imagine they would be fairly rare.

 

[Jame Rowe]

My rule of thumb is if they ask, some do and some don't.

My other rule of thumb is that no species that evolved on different planets can interbreed - if we can't interbreed with cats that evolved on the same planet as us, we can't interbreed with aliens which evolved on different planets.

 

[Bez]

I getcha.

My question wasn't restricted to breeding however.

The genetic macro-molecules (whatever form they take) define how a species is made up, as well as being the material used for replication.
So a plant-analog which has a completely different set of genetic coding will most likely not have the same nutrients as the plant found on earth, and will in all probability be indigestible (at best) or highly toxic (at worst).

Also, having a breathable and non-toxic atmosphere is the least of our worries if there are alien microbial life forms in the air. If the genetic coding of the alien microbes is totally alien to ours, then we will probably never be valid hosts for them. All good.
If it is in any way similar, then it is just a matter of time before they evolve into a form that can exploit us and then we are screwed.

 

[ShawnDriscoll]

Anything is possible in Annihilation. And The Thing. And ALIEN. Blade Runner 2049. And I'm sure in others.

 

[RogerMc]

But according to Traveller 5 although we can't interbreed with cats a sufficiently advanced lab can splice human and feline genes together to create a human-cat chimera.

And T5 even suggests that Vargr are not just uplifted canines but have human DNA and so are really wolfmen (a question which you'd assume could actually be settled with 56th century genetic science hey but this is Traveller so it is A Mystery).

Canonical Traveller uplifted species like Ursae and Dolphins are geneered and thus really chimerae as well - since where else will you get genes for intelligence than from humans.

Cordwainer Smith's Instrumentality of Man books have a civilisation where an entire underclass of chimerae serve the pure human elite - which I am sure exists somewhere in Traveller.

And I happen to be reading Alistair Reynolds brilliant Revelation Space series which has an underclass of Pig People - who are really not happy with their lot - as well as decadent aristos who remodel themselves with a bit of Zebra or what have you just for cosmetic purposes.

Logically however surely it would be harder to genesplice the more divergent the species - the most successful (other than maybe the Vargr) Traveller chimerae are human-mammal and not human-reptile splices from Terran species for instance.

The Imperium also seems to have some sort of laws against geneering sophonts just for the hell of it or there'd be considerably more variant human species like the Nexxies than there seem to be knocking around.

It seems legitimate for instance to geneer in supplementary gills for waterworlders or immunity to the atmospheric taints on so many planets but geneering a human variant that could only breathe water or methane or whatever may be a step too far?

 

[steve98052]

There are several major biological chemicals to consider:

- genetic molecules, which on Earth are right-helix DNA and RNA with four bases* encoding genetic information.
- proteins, which on Earth are built from about 20 L-chiral amino acids.
- sugars and polysaccharides, which on Earth are D-chiral carbohydrates.
- lipids, which are not usually chiral.
- miscellaneous molecules, such as polycyclics.

Each of the chiral molecules could have opposite chirality in a non-Earth biology. It is also possible that a non-Earth biology could use both chiralites in their proteins and sugars, though probably not in their genetic molecules. But L and D amino acids and sugars would not be interchangeable; a protein that was supposed to have L-lysine in a given spot wouldn't work the same way with a D-lysine there (and probably wouldn't work at all).

Although mixed-chirality molecules are possible, it seems much more likely that a biology would have just one for each type of molecule. Some research even suggests that the chiralities in Earth life are more likely, because of differences in the chirality mix in cometary molecules; if there's an explanation for that, I don't know about it.

Note that although a non-Earth biology might be strict about the chirality it uses in its life, it might be able to digest either chirality, if its environment offers both chiralities in food. But Earth life is mostly strict about chirality; L-glucose can be used as a no-calorie sweetener, because neither human biology nor human gut flora can digest it.

Next, can genetic molecules be something other than four-base DNA and RNA? Yes. Researchers modified a bacterial DNA polymerase to copy DNA with six bases instead of the natural four, and then added a gene to its genome that included the extra bases, and the bacteria faithfully copied the six-base gene (which didn't actually do anything except prove the concept) along with the normal basss.

Could they be something other than DNA and RNA? Probably. Earth biology is specific enough to ribose and deoxyribose that anything other than those sugars don't work (and closely similar sugars can be used as anti-viral and anti-retroviral medications), but if there's something special about those two sugars that make them the only ones that would work, I don't know what it would be.

However, it seems likely that the general structure of a phosphate alternating with a five-carbon sugar, each sugar bound to a base similar to the four in Earth life. It's also likelythat there would be two (or more) types of chain, a more stable one (like DNA) for genetic storage and a less stable one (like RNA) for things like messaging and protein transcription.

Proteins, sugars, and lipids all seem less likely to differ much. Sure, they can include different mixes of amino acids, different typical sugars and lipids, etc., but the general idea that chains of amino acids form enzymes, sugars store energy and are used in some structures (plant fibers in Earth life), and lipid bilayers form cell walls seems difficult for life to do another way.

* I wrote four bases for clarity, but in RNA one of the four is different from the one in DNA.

 

[Reynard]

Or we go the Niven Known Space route with a protein food goop spread across the galaxy billions of years ago by the intelligences of the time was the basis of all life to come and would have much biology in common.

 

[Condottiere]

I'm pretty sure that mushrooms are a pan dimensional lifeform.

 

[TrippyHippy]

Mushrooms are a fungi, and have a particular cellular design to categorise it as such. Viruses, also, generally have an RNA strip that integrates with a hosts DNA and other species don't have full blown DNA either.

It really isn't beyond the boundaries of science fiction that different planets have entirely different chemicals that make up their particular blueprints - and there are some quite extreme species on Earth that confound what we consider conditions of life. We base DNA and all the other developments merely on what we already know on Earth.

So no, DNA isn't necessarily universal at all.

 

[RogerMc]

Yes and this is canonical as well given that the Imperium is shortly to be destroyed by a bunch of rogue sentient sillicon chips from Cymbeline...

 

[steve98052]

Fair point about the silicon life form as canon. (But I'm a Lorenverse guy, so Signal GK is not canon for me, and the Rebellion was a ripple in Ilelish that collapsed when the news arrived there.) The silicon life form is well designed for rule of cool, but doesn't seem chemically plausible.

I suppose it's plausible for other biological polymers to store genetic information. The phosphate groups in DNA and RNA may not be necessary; the backbone of the genetic polymer could be a polysaccharide with base groups but without the the phosphates, or a polypeptide with base groups, or even a protein as in prions, assuming the prion hypothesis is correct.

Getting to biochemistry questions that can affect gaming, there are just a few matters to consider:

Can we eat this? If it's a polysaccharide or protein of the wrong chirality, the answer is "not really". Yes, you can eat it, and it won't hurt you, but you can't digest it, so you might as well be eating cardboard. Even if it is the correct chirality, you may not be able to digest it; cellulose is a very common Earth polysaccharide, but we can't digest it. However, a high-technology society might be able to genetically engineer a fermentation bacterium that can digest an alien plant into something humans can eat. A low-technology society might discover a naturally occurring fermentation microbe that does the same. Maybe that's what the prehistoric Vilani cook caste were the keepers of such a family of microbes, possibly natural, possibly engineered by the Ancients so that the proto-Vilani could eat on Vland.

"Welcome to our planet. If you're staying long enough that you want to eat the local cuisine, you'll need to take gut flora capsules and eat enough local plantish to feed the flora, and enough import grub that you don't starve in the meantime. You'll know you're ready for a local diet when your poop is brown again, instead of that fluorescent cyan some of you may have observed."

Can it eat us? If it's big enough, it probably can. It might spit you out as indigestible, but that's not much consolation if it bit you in half before discovering that you don't taste like food.

Can we interbreed with it? No. But that might not prevent some few people from trying.

Can it make us sick? Probably not, but it's a good idea to read that Scout service biological safely guide.

 

[RogerMc]

Although there are still Cymbeline Chips in the Lorenverse and even potentially Virus - it is just that without the assassination, rebellion and civil war it is never going to be deployed.

Incidentally has anyone ever thought of running a mirror universe campaign where an imperial cruiser from the nice peaceful Lorenverse in1127 misjumps into the Rebellionverse and has to stop their own evil goateed mirror selves from nuking rebel planets in the name of Lucan?

 

[Nobby-W]

[ . . . ]
The question is whether the self-replicating macro-molecules that are universal in all life on Earth (DNA/RNA) are also present on other worlds?
Obviously, worlds which were seeded by The Ancients will have species that have DNA or RNA, but what about other worlds, with completely alien species present?
[ . . . ]

Some sort of programmable protein (or protein analogue) synthesis mechanism would be necessary for cellular life to reproduce. Its not necessarily a given that DNA/RNA is the only mechanism that could do this, but it's the only one that's been found to occur naturally (extremophiles still use it). I dare say that another mechanism could be found with a suitable research programme, although I'm not aware of this being done.

Given its success on Earth, it's a reasonable assumption that extraterrestrial life might also use it. DNA is likely to be the most efficient mechanism for earth-like conditions - if something else worked significantly better it's quite likely that life using that mechanism would have displaced DNA-based life. Given that DNA has been demonstrated to work in a variety of conditions (by extremophile life) it's also quite likely that it could work in biomes with significantly different conditions from earth.

This implies that a lot of alien life might use proteins similar to those found in terrestrial life and therefore might have similar biochemistry - although it might still have some toxic chemicals in it. If some alien life form used a different mechanism then it's quite likely that its equivalent to proteins could have quite different chemistry.

 

[Reynard]

"since where else will you get genes for intelligence than from humans"

It's assuming we have an in depth understanding what the biology and mechanics of what makes a creature 'intelligent'. The process isn't making another life form more human but giving their biology the necessary tweaks to run an equivalent to what we consider intelligence.

On a similar note, vargr don't have human hands per se. Their paw structure was elongated and restructured for grasping and manipulation. If you were to see a vargr hand, I'll bet you can see a lot of similarity to the original paw.