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Could there be an unknown class X of biomolecules that was involved in the origin of life but was later outcompeted by the DNA + RNA + protein combo that domina
by divbzero 4y ago
Could there be an unknown class X of biomolecules that was involved in the origin of life but was later outcompeted by the DNA + RNA + protein combo that dominates today? This class X could have been less efficient at replication but kinetically easier to form from the primordial broth.
- stainablesteel 4y agoit would likely be something of a hybrid nature or an extremely similar precursor, nothing drastically different
- ncmncm 4y agoThe environment at the time life evolved was very, very different from today. In particular, free oxygen was practically non-existent. Metals, particularly iron, and metal complexes were dissolved in the water at high concentration. Processes that spawned the first life had to be compatible with all of that, and may well have depended on many details of it, most of which we can barely imagine. The ancestors of everything alive today survived the arrival of free oxygen a billion or two years later, with the loss of most dissolved metals, leaving no trace of the overwhelming majority that failed to adapt to that. Conditions today, even without competition from existing life, might be wholly unsuitable for biogenesis.
- exyi 4y agoFor sure it's possible, but evolution rarely gets completely rid of something (as far as we know). My favorite support for RNA-world (and similar) hypothesis is that RNA molecules are used as enzymes in some processes (ribosome - translation), even though RNA is a pretty bad catalyst. If the evolution could choose, it would most likely use a protein, but the cost of switching to "new tech" is too high.
- zmgsabst 4y agoThey’re mentioned elsewhere, but viroids[0] are another example of RNA acting as enzymes[1]. [0] https://en.wikipedia.org/wiki/Viroid https://en.wikipedia.org/wiki/Viroid [1] https://en.wikipedia.org/wiki/Ribozyme https://en.wikipedia.org/wiki/Ribozyme
- axytol 4y agoHow about prions[0] or something similar? They replicate, and are much simpler and smaller than RNA or DNA based replicators. [0] https://en.m.wikipedia.org/wiki/Prion https://en.m.wikipedia.org/wiki/Prion
- COGlory 4y agoThey don't replicate, they take other proteins and refold them. They need existing protein to do that.
- gus_massa 4y agoI agree, but I want to add two bad metaphors. (I'd like to have a good one, but I only have bad ones.) * Prions are like falling domino pieces. If you have a lot of standing domino pieces, and one of them falls, it may cause other domino pieces to fall. But they don't create more domino pieces, or standing pieces. They just pull down the pieces that are around. Also, they store no information, they just flip a bit from 0 to 1. * RNA is like a small pile of glued magnets glued on their side. If you put some glued magnets in a box full of magnets and shake them, they will pick other magnets and create a inverse copy. If the side of the magnets is (magically) sticky, the copy may get glued permanently. After some more shaking, you have two piles of glued magnets moving around and collecting more magnets and making copies. They store information, because the initial pile may be NNSNSNS and the new piles will have the same pattern until there is an error in the copy.
- COGlory 4y agoThose are interesting analogies, particularly for the RNA. Thanks for sharing them.
- gus_massa 4y agoThanks. I agree that they are interesting. (I wrote them :) .) But I can think a few reasons why they are wrong. Anyway, I think they are useful to understand the difference between prions and rna, and why prions are not a good proposal for the origin of life.
- dtgriscom 4y agoFrom [0]: > A shadow biosphere is a hypothetical microbial biosphere of Earth that would use radically different biochemical and molecular processes from that of currently known life. Although life on Earth is relatively well studied, if a shadow biosphere exists it may still remain unnoticed, because the exploration of the microbial world targets primarily the biochemistry of the macro-organisms. [0] https://en.wikipedia.org/wiki/Shadow_biosphere https://en.wikipedia.org/wiki/Shadow_biosphere
- edgyquant 4y agoThat isn’t what they’re asking at all. They’re asking about a pre-cellular life like virus that evolved into ours that was then outcompeted.
- gus_massa 4y agoNobody is sure. Look at https://en.wikipedia.org/wiki/RNA_world#Alternative_hypotheses https://en.wikipedia.org/wiki/RNA_world#Alternative_hypothes... It has three alternatives PNA, TNA and GNA that are somewhat variants of the RNA. (I'm not an expert, but my uninformed opinion is that GNA looks promising.) Also PHAs that is very different and the iron-sulfur idea that is even more difficult. (I'm not an expert, but my uninformed opinion both look too weird and the transition to DNA is less clear.)
- edgyquant 4y agoTNA is actually observed existing in stellar nurseries so it’s a likely pre-RNA candidate.
- gus_massa 4y agoI imagined a closed 4-crbon sugar, and I discarded the idea. Is theose open in the TNA? Is the 3D structure similar to the structure of a closed ribose? (My 3D imagination for sugars is very bad.)