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Widdekind

Hadean Eon pre-Life was un-catalyzed 'slow life' ??

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Early earth life lacked bio-catalysts, which speed up the assembly, of protein poly-peptides:

 

tRNA molecules evolved before the present set of aminoacyl-tRNA synthetases (Wiki)

Now, chemical reactions can occur, without catalysts -- even as one can 'walk to work', without taking the turbo-charged car. And, pre-Life, upon this planet, was surely simple and 'stripped down', to the maximal minimum. Could early earth pre-Life, then, have been 'slow life', which 'walked unaided', ponderously pursuing bio-chemical reactions, which are rather rapid today, b/c of catalysis ??

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The supposition regarding tRNAs predating their synthetases is not that life was uncatalysed before that, but that there was a different set of catalysts before the current ones emerged. Specifically, the authors of that paper your quote is referring to suggest that a catalytic RNA may have been the catalyst before the later aminoacyl-tRNA synthetases.

 

For an example see this paper: Aminoacyl-RNA synthesis catalyzed by an RNA (Illangasekare et al. 1995)

 

And I believe the most commonly (but not universally) accepted idea is that mineral surfaces or clay matrices acted as catalysts for the initial synthesis of complex organic molecules. I'm no expert, but I think the reactions are not thermodynamically favourable enough to make products in any significant concentration, so that any form of catalyst is more likely than none.

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Thanks for that clarification. According to Wiki:

 

the molecular phylogenies of aaRSs are often not consistent with accepted organismal phylogenies, e.g. they violate the so-called canonical phylogenetic pattern shown by most other enzymes for the three domains of life - Archaea, Bacteria, & Eukarya. Furthermore, the phylogenies inferred for aaRSs of different amino acids often do not agree with one another. These are two clear indications that horizontal transfer has occurred several times during the evolutionary history of aaRSs

Does such suggest, that aaRS's had only recently evolved, and were in 'unfinalized form', c.4 Gya, during the days of 'proto-Life' (LUCA) ?

 

What about more advanced pre-Life (advanced RNA-world) ? Pure RNA does not self-assemble, into strands, longer than 50-100 base-pairs (bp) (Lane. Life Ascending, p.50~). However, the basal bacteria, on the earth phylogenetic tree, all have >1.5 Mbp. And, the simplest bacteria, Pelagiobacter ubique, has ~1.2 Mbp. Such suggests, that the Last Universal Common Ancestor (LUCA), of all earth microbes, had ~1 Mbp in its DNA ring. So, pre-Life, in the RNA-world, had ~100 bp ("log 2"); whereas, proto-Life, LUCA, had ~1 Mbp ("log 6"):

 

pre-Life
(RNA-world)
:
~100 bp
("log 2")

...

proto-Life
(LUCA)
:
~1 Mbp
("log 6")

Now, RNA can combine with Proteins, into RNP complexes. And, 'stabilizer Proteins' can strengthen those structures (Scientific American [April 2011], p.73). And more, RNA has been interacting with Proteins, from the first efforts, of earth life. So, such suggests, that, before DNA evolved, as a "durable deep storage" biochemical 'upgrade' of RNA, protein-stabilized RNPs could have accommodated increasingly complex genetic codes, for increasingly complex bio-chemical life, before the evolution of full-fledged cells, like LUCA, at ~1 Mbp.

 

So, interpolating, between pre-Life & proto-Life, perhaps 'advanced pre-Life' had genomes of ~10 kbp ("log 4"), stored in stabilized RNP complexes. And, genomes of such length, are reminiscent of archaic RNA retro-viruses. And more, a retro-virus 'virion' super-complex, as a (colossal) combination of RNA & Proteins, is, technically, an RNP. Perhaps, then, advanced pre-Life, was (retro-)viral, employing Protein 'plate armor' protected retro-virional-like RNP super-complexes, to stably store their genetic codes, which were then thousands & tens of thousands of bp long.

 

pre-Life
(RNA-world)
:
~100 bp
("log 2")

advanced pre-Life
(retro-virions)
:
~10 kbp
("log 4")

proto-Life
(LUCA)
:
~1 Mbp
("log 6")

The retro-virional RNP super-complexes would have functioned only as genetic code, and would have relied on a surrounding bio-chemical system of pathways, to access and translate said code. If the RNA-world was housed, in the pores of undersea hydrothermal vents, then that bio-chemical 'support system', would have been housed, in those undersea vents.

Edited by Widdekind

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