Genetic code other than DNA (moved)

[KingGambit]

Summary: Curious to find out genetic code other than DNA
<mentor> Moved to Discussion, hypothetical discussion
Dear PF Forum,

It's been a long time since I log into PF. And I hope everybody is in a good health.
Recently I had a discussion debate with my friend about other life in this universe. I told him that I didn't know that there is other life in this (observable) universe. I told him that at least from the number of stars and planets and goldilock zone and abundant elements, carbon, nitrogen, oxygen, still I can't say that there is a certainty other life in this (observable) universe.
And he said, that, it shouldn't have been carbon. Perhaps iron or sulfur or helium. Then, I cut him sharply. Not helium!

But I am just thinking. Perhaps this very simple question first.
Could there be other genetic code besides DNA. I mean besides ATGC or uracil. Molecules that can replicate themselves?
It could be carbon or silicon or anything based, just molecules that can replicate.

Thank you very much.

 

[Vanadium 50]

Probably. But if you want us to give you a demonstrated working example (other than variations like RNA), of course we can't.

 

[pbuk]

https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry

 

[symbolipoint]

Maybe only wild guess, but maybe, organelles of the cell, other than the nuclei?

 

[Borek]

Broadly speaking carbon is the only element capable of producing chemistry diverse enough to support complexity required by biological systems.

There were definitely published suggestions that some other system could exist before the RNA world, although it is not clear to me if it will count as "other" genetic code in the context of your question. What is proposed is that there was some other framework than RNA for the structure, but it doesn't necessarily mean other nucleobases for coding.

 

[Vanadium 50]

carbon

I don't think you have to give up carbon (although maybe B-N chains could be made to work), just replace a hydrogen here and there by a methyl group or maybe a halogen if you want to get funky.

 

[Godot_]

Broadly speaking carbon is the only element capable of producing chemistry diverse enough to support complexity required by biological systems.
[...]

In brief:

If you look at other atmoshere types and temperature ranges, there might be a few different options.

Most probably not with our atmosphere's redox potential and temperature range.

Unless you'd count slightly different backbones (i.e. those with sugars other than (desoxy-)ribose), or a different set of nucleotide bases, which are theoretically possible.

The same holds true for enantiomeric biochemistries (i.e. D-amino acids instead of the universal L-AAs). This is supposedly a thing that was 50/50 in the earliest life, and the L-AA type just prevailed or the D-AA-based life just never happened. Those lifeforms probably/supposedly would have enantiomeric DNA/RNA.

Also, there actually are a few more nucleotides in addition to ACGT/U, but they're pretty rare. Unless you count the modified ones in ribosomal RNAs, which are ofc abundant. But those aren't coding NAs, they're more relevant to their ribozyme function, and IIRC created by a post-transcriptional modification anyway.

Further variants are created by methylation (5-methylcytosine) or other modifications - which is covered by the field of epigenetics. Those are have to be duplicated during replication, too - otherwise methylation patterns would get lost after a few cell cycles... ...but they initially are created by post-DNA-duplication modification.

 

[Borek]

If you look at other atmoshere types and temperature ranges, there might be a few different options.

Care to list them? All I ever saw were speculative suggestions not seriously based on what we know about chemistry of other elements (and it is not like we haven't tried quite exotic combinations in quite exotic conditions - there is just no thermodynamics nor kinetics that would support systems versatile enough).

My take is that if we spend hundreds of years looking for something, using best existing tools and throwing at the problem best minds, and we still didn't found it - it suggests assumption "it is there" was faulty from the very beginning.