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I was thinking prions might be a good candidate for OOL. Early Earth apparently was rich in amino acids and so chains of them may have formed natural proteins.

I was thinking prions might be a good candidate for OOL. Early Earth apparently was rich in amino acids and so chains of them may have formed natural proteins. So a prion - a functional protein that can change other proteins into its shape - would be able to set off an evolutionary fitness search for the protein which could best "convert others" while resisting being changed by others. The other reason is I'm skeptical of starting with a polymer type information encoding molecule. It seems too unlikely that any minimally viable genetic molecule could assemble by pure chance and there is not a good way for information to flow from the environment/cell -> genetic polymer.

dexwiz 10y ago
That is an interesting idea, that proteins (or proto-proteins) predate genetics. Now I am trying to think about how proto-proteins would have first evolved towards creating genetic polymers that replicate themselves. Or maybe the genetic polymer was the best self replicating pattern, and life evolved as a side product?
lawpoop 10y ago
I personally am a fan of the RNA world hypothesis: https://en.wikipedia.org/wiki/RNA_world https://en.wikipedia.org/wiki/RNA_world RNA can act as both a store of information, and as an enzyme catalyzing reactions. In this theory, certain sequences of RNA would be the original self-replicating molecules. Over time, variations in their replication would give rise to other enzymes for specialized reactions, and DNA as a pure-data store. Jack Szostak has done an excellent series of short videos on the theory, and he and his students have done a surprising amount of experiments to support the theory. https://www.youtube.com/watch?v=PqPGOhXoprU https://www.youtube.com/watch?v=PqPGOhXoprU
ars 10y ago
A prion can change the shape of other proteins, but can't make proteins.
- gus_massa 10y ago
  I agree that prions are bad candidates. They can only change the shape of one specific protein (perhaps a small family of proteins). To get something that is barely alive it must be more general.
entee 10y ago
Why does the genetic nature of the polymer as a record of its function need to be the primary purpose for the original ancient life-like polymer? You identify the prion as a good candidate, but it's just a polymer that can do some sort of reaction (change the shape of another protein). By that score RNA is pretty great. We know it can do chemistry, and that might have been its primary purpose at first. It's possible that only later did the fact that it could store genetic information in the way we understand it today become useful. We have at least some evidence to believe that RNA was the first "living" molecule in that arguably the most primitive enzymes we have (ribosomes) are an RNA-protein hybrid, with some evidence to suggest the RNA was there first and protein bits were added/swapped out to make it better. It's also possible that a slightly simpler version of RNA was first and that the more complex bases came later. But all of these polymer monomers existed in the primordial soup, I don't understand why a protein polymer would be more likely to arise than an phospho-sugar one. Indeed the basic unit of energy inside pretty much all cells is ATP (one of the monomers in RNA), another sign that early life was very closely tied to phospho-sugar monomers.
the8472 10y ago
> It seems too unlikely that any minimally viable genetic molecule could assemble by pure chance We don't need to jump from abiotic to minimal self-sustaining life as we define it today. We can have intermediate steps of funky proto-life chemistry that only work under very specific, local conditions, feeding of abundant molecules and being aided by some other abiotically created catalysts. Molecules might not even start with self-replicating directly, some might just indirectly catalyze their own precursor molecules and then self-assemble to 99% junk, 1% similar to itself. You also consider that it did not have other organisms to compete with. Even very low success rates at synthesizing precursor molecules or self-replication would still outcompete any process that has zero or negative feedback. https://en.wikipedia.org/wiki/Ribozyme https://en.wikipedia.org/wiki/Ribozyme https://en.wikipedia.org/wiki/Abiogenesis#Autocatalysis https://en.wikipedia.org/wiki/Abiogenesis#Autocatalysis

dexwiz 10y ago

That is an interesting idea, that proteins (or proto-proteins) predate genetics. Now I am trying to think about how proto-proteins would have first evolved towards creating genetic polymers that replicate themselves. Or maybe the genetic polymer was the best self replicating pattern, and life evolved as a side product?

lawpoop 10y ago

I personally am a fan of the RNA world hypothesis: https://en.wikipedia.org/wiki/RNA_world https://en.wikipedia.org/wiki/RNA_world RNA can act as both a store of information, and as an enzyme catalyzing reactions. In this theory, certain sequences of RNA would be the original self-replicating molecules. Over time, variations in their replication would give rise to other enzymes for specialized reactions, and DNA as a pure-data store. Jack Szostak has done an excellent series of short videos on the theory, and he and his students have done a surprising amount of experiments to support the theory. https://www.youtube.com/watch?v=PqPGOhXoprU https://www.youtube.com/watch?v=PqPGOhXoprU

ars 10y ago

A prion can change the shape of other proteins, but can't make proteins.

gus_massa 10y ago
I agree that prions are bad candidates. They can only change the shape of one specific protein (perhaps a small family of proteins). To get something that is barely alive it must be more general.

entee 10y ago

Why does the genetic nature of the polymer as a record of its function need to be the primary purpose for the original ancient life-like polymer? You identify the prion as a good candidate, but it's just a polymer that can do some sort of reaction (change the shape of another protein). By that score RNA is pretty great. We know it can do chemistry, and that might have been its primary purpose at first. It's possible that only later did the fact that it could store genetic information in the way we understand it today become useful. We have at least some evidence to believe that RNA was the first "living" molecule in that arguably the most primitive enzymes we have (ribosomes) are an RNA-protein hybrid, with some evidence to suggest the RNA was there first and protein bits were added/swapped out to make it better. It's also possible that a slightly simpler version of RNA was first and that the more complex bases came later. But all of these polymer monomers existed in the primordial soup, I don't understand why a protein polymer would be more likely to arise than an phospho-sugar one. Indeed the basic unit of energy inside pretty much all cells is ATP (one of the monomers in RNA), another sign that early life was very closely tied to phospho-sugar monomers.

the8472 10y ago

> It seems too unlikely that any minimally viable genetic molecule could assemble by pure chance We don't need to jump from abiotic to minimal self-sustaining life as we define it today. We can have intermediate steps of funky proto-life chemistry that only work under very specific, local conditions, feeding of abundant molecules and being aided by some other abiotically created catalysts. Molecules might not even start with self-replicating directly, some might just indirectly catalyze their own precursor molecules and then self-assemble to 99% junk, 1% similar to itself. You also consider that it did not have other organisms to compete with. Even very low success rates at synthesizing precursor molecules or self-replication would still outcompete any process that has zero or negative feedback. https://en.wikipedia.org/wiki/Ribozyme https://en.wikipedia.org/wiki/Ribozyme https://en.wikipedia.org/wiki/Abiogenesis#Autocatalysis https://en.wikipedia.org/wiki/Abiogenesis#Autocatalysis