The most primitive adapter molecule on Earth
Origin of Life
To evolve life requires an adapter molecule.
An adapter molecule links an amino acid to an RNA.
tRNA is the adapter molecule in living systems on Earth.
ACCA-Gly was the primitive adapter on planet Earth.
Multiple ACCA-Gly can interact with a GCGGCGGCGGCG repeat. With wet-dry cycles, one could make polyglycine in a laboratory using ACCA-Gly as the primitive adapter.
ACCA-Gly was attached to many RNAs, including tRNAs, to support tRNA evolution.
In tRNA, tRNA-73 becomes the discriminator base. Aminoacyl-tRNA synthetases (the enzymes that attach an amino acid, i.e., glycine, to a cognate tRNA) use the discriminator base as one indicator of what cognate amino acid to attach to which cognate tRNA decreasing protein synthesis errors.
The 74-CC-75 sequence interacts with a GG sequence in the peptidyl site within the peptidyl-transferase center of the ribosome.
In tRNAHis, tRNA-73C is present. This could be a problem for orientation of tRNAHis-peptide in the peptidyl site of the peptidyl-transferase center of the ribosome leading to protein synthesis errors.
So, a system evolved to modify the 73-CCCA sequence in tRNAHis by pairing a tRNA(-1)-GTP opposite tRNA-73C. This enzyme is as ancient as the genetic code and was necessary to evolve the code.
So, in tRNAHis-peptide, ribosome peptidyl site GG recognizes accurately tRNAHis-74-CC-75 and the peptide chain is properly oriented.
Without a genetic code, there is no life.
Chemical Evolution of Life on Earth
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