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I've read that the first protein synthesis has likely included translation by readily formed tRNA-like adapters. The other alternative is that primordial 'mRNA's didn't need adapters and instead themselves crudely directed amino acid sequences.

However, to me, the former assumption seems problematic: if adapters did indeed exist, how could they bind to the mRNAs (or an equivalent molecule) without the intervention of its copy forming? Both the adapters and the copy most have been sequences of nucleic material, and so, logically, it would follow that bonds with the mRNA molecule would form under similar conditions. Evidently, though, they did not, or else the adapters and the copy would all get mixed up.

My question, then, is: how could it naturally be that two molecules made of the same material form bonds with the same substance under different conditions? Furthermore, these conditions must be very specific: the activation energy needed to trigger bond formation with adapters must be higher or lower than that required to break or form bonds with a copy, respectively. For this to be true just by pure chance requires a very lucky coincidence.

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  • $\begingroup$ What does "the intervention of its copy forming" mean? What does "it" refer to there? For proto-protein formation, there would not need to be formation of a copy of any RNA sequence. The proto-tRNA piece would, in addition to generally holding an amino acid would have a section that was complementary to a 2- or 3-base proto-codon. The sequence of proto-codons for the protein would not need to be copied into a separate mRNA molecule as happens now in the DNA-RNA world. $\endgroup$ – mgkrebbs Aug 22 '18 at 3:59
  • $\begingroup$ @mgkrebbs yeah, when I say day mRNA, I actually mean just the self-replicating molecule. "It" refers just to that molecule. Why a copy doesn't need to be formed, it necessarily will under the right conditions. And the conditions will be right, as we know tRNAs are able to bind to the self-replicating molecule. This results in a mix of some parts forming a copy of the self-replicating molecule and the other parts bound to tRNAs. This, evidentIy, isn't the case. What I want to know is why. $\endgroup$ – Max Aug 22 '18 at 7:55

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