3 ms·
One of the suggested possibilities is that there was a pre-RNA molecule, such as PNA[1]. PNA is less efficient but it's much more durable, simpler to form, and
by hwillis 10y ago
One of the suggested possibilities is that there was a pre-RNA molecule, such as PNA[1]. PNA is less efficient but it's much more durable, simpler to form, and can self-polymerize above boiling. If you had enough PNA in one place and got it relatively hot, it would spontaneously form "genes" which would be stable for an extremely long time. They would just float around, and any time they came into contact with enough PNA they would be able to replicate. It would be a relatively slow process, but purely random and so would quickly gravitate towards optimization.
RNA can do the same thing. Transcriptase and polymerases are catalysts but they are not strictly necessary. Simple RNA can have a lifespan of hundreds of years and it just needs to replicate more than once to propagate. Over time a primitive polymerase would eventually be made by freak chance and mutation, and then everything would kick off.
Once you have polymerase natural selection would speed up massively and become resource-limited rather than reaction-limited. Thats when a metabolism would evolve, and enzymes that were successful at catalyzing the conversion of material into resources would stimulate local growth. You'd still only have a frothy mess of chemicals, but it would be a frothier mess than the surrounding mess. The first organism to make some kind of container wins- most likely they'd evolve mucus-y proteins that would help keep their resources concentrated. Over time that mucus would give way to a hollow bubble, which would then become a lipid layer, which would then become the first cell.
[1] https://en.wikipedia.org/wiki/Peptide_nucleic_acid https://en.wikipedia.org/wiki/Peptide_nucleic_acid
- mtdewcmu 10y agoI think the fundamental problem is that a strand of PNA floating in water is just a strand of PNA floating in water. It isn't an organism, because organisms do things, things that require inputs of energy. I don't see how this lonely strand of PNA ever figures out how to spontaneously give itself a metabolism. Without having a metabolism to begin with, that PNA strand will never do anything.
- hwillis 10y agoThe metabolism is to simply wait for resources to react naturally. PNA in sufficient concentrations and conditions will continue to polymerize and grow just by random chance. It's not any different from what happens inside a simple cell, really: ATP and other resources are for the most part just present inside the cell. It's just that for life to come about those conditions or something like them have to exist naturally. As the RNA/pre-RNA chain grows, there will be natural selection for any sequences that catalyze polymerization. This will eventually either lead to self-catalyzing replication or a mutual replication. AFAIK the second one is considered more likely because although RNA can self-catalyze it's not very good at it (of course, it doesn't really need to be). Mutual replication would require a primitive polymerase being spontaneously generated, which would allow an RNA-like molecule to -self-replicate. Eventually an chain would be created that could replicate via copies of itself, and that molecule would be able to spread beyond the original catalyzing molecule and outcompete anything else (since it would be able to replicate with any copies it made, it would grow exponentially rather than linearly).
- mtdewcmu 10y agoMy proposal is basically that the proto-organism has to learn to eat before it can do anything else. The processes that you have described could still have important roles to play.