If not DNA, then what?

[gestaltist]

I remember Zompist mention that life on Almea is not DNA-based. What is the internal organization of life then? Has this been explained somewhere?

[Aldwinkle]

Magic?

[Neon Fox]

"Some heritable physical thing that is not deoxyribonucleic acid." "They don't have DNA" is not at all the same thing as "They're based on magic"; DNA is a very specific molecule. Saying they don't have DNA just means that the thing they use to pass traits to their offspring is, well, not DNA. And since they didn't develop on Earth, that's not even remotely surprising. What is surprising is that Terrans could digest Almean food!

[Aldwinkle]

"They don't have DNA" is not at all the same thing as "They're based on magic"; DNA is a very specific molecule.

Outside of RNA (kinda - RNA is not very stable), there are no known methods for such things. Hence whatever choice is made for this will be pulled from a buttocks, which is basically magic???

Unless he goes with whatever previous theory they used, such as Schrödinger's aperiodic crystal ?

[Neon Fox]

Dude, these are people from another planet. They have some huge, complex organic molecule that does the job, and it's not DNA. That's not "pulling out of one's ass", it's a simple statement that fails to needlessly multiply entities. We know quite a bit about how Almean magic works, and none of it is particularly suitable for being Almean genes; organic chemistry is a much better place to look.

[zompist]

Neon Fox has it.

Alternatives to DNA/RNA have been created in the lab.

Prions are non-DNA, can reproduce themselves, and can evolve, though I don't know how you'd build a biology on top of them. They can be used to modify genes though.

(Not the same thing, but interesting: there are also alternatives to the common genetic code. Some of them choose amino acids that are normally unavailable, and thus create novel proteins.)

[GreenBowTie]

the Novel Proteins would be a great band name

[gestaltist]

Neon Fox has it.

Alternatives to DNA/RNA have been created in the lab.

Prions are non-DNA, can reproduce themselves, and can evolve, though I don't know how you'd build a biology on top of them. They can be used to modify genes though.

(Not the same thing, but interesting: there are also alternatives to the common genetic code. Some of them choose amino acids that are normally unavailable, and thus create novel proteins.)

Thanks for confirming, Zomp.

What does it mean for the Ellenikoi, by the way. They shouldn't be able to cross-breed with Almean humans, and would have trouble digesting Almean food.

[zompist]

What does it mean for the Ellenikoi, by the way. They shouldn't be able to cross-breed with Almean humans, and would have trouble digesting Almean food.

Indeed, they couldn't crossbreed with Almeans. Their line continued only by adoption. (There was one earth-human born on Almea but he had no one to reproduce with.)

As for food, possibly enough proteins are shared that they could get by.

[gestaltist]

Cool, thanks for clarifying. It is interesting how engrossing Almeopedia can be. Or maybe I’m just a weirdo who enjoys reading encyclopedia entries.

[Mornche Geddick]

Any genetic material must fulfil several conditions:

1) The molecule must be stable. That is the problem with RNA and why it tends to be used as temporary transport copies and catalytic molecules (like ribosomes) rather than the permanent genetic material of most organisms.

2) It must be copyable.That is the problem with proteins, and why they are at the end of the information flow, not the beginning. DNA has a regular shape (the B-form double helix) which is recognised by the synthesis enzymes, or polymerases. It also contains two pairs of bases which fit together: adenine-thymine and cytosine-guanine. A DNA molecule is synthesised nucleotide by nucleotide. Working from an intact single DNA strand, the nucleotide with the correct base is fitted into place by the polymerases. They can tell which is the right base because a) it has the right number of hydrogen bonds and b) the wrong nucleotide would make the double stranded helix irregular. (Cells contain a plethora of DNA repair enzymes which run over the DNA molecule looking for bulges and lumps, and when they find one, they cut out the offending nuclelotide and replace it.)

Amino acids don't form pairs which recognise each other, and what's more, the protein chain is often folded in a complex topology, which is energetically unfavourable for hypothetical protein polymerases to unwind. That leads to my last point.

3) The energetics must be favourable. The energy required for enzymes to run along the DNA chain, to pull the strands apart, to cut the backbone and religate it, must all be exactly right - not so large that the processes are too slow or impossible, and not so little that the DNA is in danger of disintegrating by itself. I don't know what the possible energetics of XNA and TNA are, but I suspect that this is the reason why different nucleic acids have been synthesised in the laboratory, but only two are used by life on Earth.

However, Zompist doesn't need exotic nucleic acids to make sure the Almeans and us are incompatible. One possibility is to keep the same set of four nucleotides and twenty amino acids but alter the genetic code. Each amino acid is derived from one or more nucleotide triplets out of a set of 64 (4^3). Reassign the triplets, and bingo - new genetic code.

(It would mean that we were immune to Almean viruses (and vice versa), because viruses depend on the host's polymerases to synthesise their proteins, and a host with a different genetic code would produce nonsense polypeptides from virus genes.)

Furthermore, even closely related species on Earth are genetically incompatible. There have been attempts to cross-fertilise human sperm and chimpanzee eggs (and vice versa) but there are no recorded successes.

[Mornche Geddick]

On the other hand, to digest Almean food, we would only need them to have the same biochemical building blocks - the twenty L-amino acids, the D-sugars and the triglycerides, and enzymes capable of breaking the (limited number of) bonds between them.

[hwhatting]

There have been attempts to cross-fertilise human sperm and chimpanzee eggs (and vice versa) but there are no recorded successes.

They tried that? Every time I read how much of our Genome we share with chimps, I thought that this would be one thing scientists would probably never try, for ethics reasons. I should have known better than that....

[Mornche Geddick]

Ilya Ivanovich Ivanov tried it in the 1920s.Ethics were less rigorous then.

[hwhatting]

Ilya Ivanovich Ivanov tried it in the 1920s.Ethics were less rigorous then.

Interesting, and it fits the times. After all, that was the period when Bulgakov wrote Собачье сердце ("Heart of a Dog"), about a dog who is transformed into a human by an operation.
From the article, it seems that Ivanov's attempts were rather inept, and then he was unlucky with his apes dying on him, to boot.

[Torco]

What is surprising is that Terrans could digest Almean food!

Why? I mean, food is for the most part sugar, fat and protein, right ? and sugar is a trivial molecule which every plant on earth does, it's not terribly surprising that almean plants might use sugar and its various composites <fructose, starch, whatever> just like earth plants. Same with fat, fats are not an implausibly thing for aliens to produce as part of their metabolic processes... probably some of the almean food would be indigestible for terrans, but it surely can be the case that they can get most of their nutritional needs. Vitamins are generally not inpossible things to find, unlike DNA which is highly specific and it would be less likely for aliens to produce it just like we do.

On the other hand, aminoacids are complicated: people can survive eating whatever proteins, as long as they manage to get their hands on eight aminos, called essentials, which our bodies cannot produce: but then again, it's just eight aminos, out of the twenty-somethin that there are: it's not impossible that they could find those substances in a varied diet.

[Neon Fox]

What is surprising is that Terrans could digest Almean food!

Why? I mean, food is for the most part sugar, fat and protein, right ? and sugar is a trivial molecule which every plant on earth does, it's not terribly surprising that almean plants might use sugar and its various composites <fructose, starch, whatever> just like earth plants. Same with fat, fats are not an implausibly thing for aliens to produce as part of their metabolic processes... probably some of the almean food would be indigestible for terrans, but it surely can be the case that they can get most of their nutritional needs. Vitamins are generally not inpossible things to find, unlike DNA which is highly specific and it would be less likely for aliens to produce it just like we do.

On the other hand, amino acids are complicated: people can survive eating whatever proteins, as long as they manage to get their hands on eight aminos, called essentials, which our bodies cannot produce: but then again, it's just eight aminos, out of the twenty-somethin that there are: it's not impossible that they could find those substances in a varied diet.

You've got it right there: amino acids. Apparently, Almea uses at least most of the same ones we do, at least all the ones humans can't synthesize on their own (though I wouldn't be surprised if the Elenicoi had a lot of Fun With Intestinal Upheaval, and had to eat more than an Almean would to maintain their weights). And it's a good thing that Almean sugars and amino acids have the same chirality as their Earth equivalents, or the Elenicoi would have quickly starved to death...

[Neek]

Perhaps it didn't take long for their gut fauna to adapt to a new source of energy? After all, necessity is the mother of invention, evolution included. On the other hand, I would argue that whichever divine entity that brought them over would at least look into that as a potential problem. You don't transport people across the universe to send a message about the Lord and Savior and forget to pack them a lunch. It might be a cop-out of an explanation for their ability to digest Almean food, but hey, it could at least explain why they didn't die of anaphylactic shock from alien allergens in their food, in the air, wherever.