The Mystery of Stop-Codons....

Hi, semilanceata. Welcome to EvC! I'm not a cellular biologist or geneticist, but it seems to me that the answer could very well be simple. tRNA has to encoded by DNA. Each different tRNA in an organism would have to be encoded by a different gene, each of which would either arise independently or as a variation of the first tRNA gene. Either way, they would have arisen one by one.Seeing how an "end" to a coding region is advantageous for condensing the genome into just a few chromosomes or plasmids, I see no reason why this condition would be selected against, thus it would be preserved and amplified in the succeeding generations. On the other hand, an organism that continues to produce new genes encoding tRNAs with "unused" anticodons, would reduce its ability to end a polypeptide and condense its genome, creating a greater inefficiency in transcription/translation.{AbE: I can't confirm to you that this is correct: maybe Wounded King or other geneticist/molecular biologist could shed some light on this?}Edited by Bluejay, : Addition

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I'm Thylacosmilus.Darwin loves you.

Thank you, molbiogirl. I'm glad you do translations, too: my molecular biologyese isn't very good (but it's a lot better than my Teslaese). And, it would appear to pose a serious challenge to my hypothesis. Unless...From your wiki quote:

quote:

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In certain proteins, non-standard amino acids are substituted for standard stop codons, depending upon associated signal sequences in the messenger RNA...

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The presence of an auxiliary signal here indicates to me that the initial function of the codon was "stopping," and that the non-standard aminoacylation is a derived function. So, perhaps my model is still intact.I read up a bit on Wikipedia, and I found that the signal is a SECIS element, which is just a short sequence of non-naturally-pairing nucleotides right after the UGA that's supposed to code for selenocysteine. Somehow, that assists the selenocysteine-carrying tRNA in binding to the stop codon. This also implies that the UGA codon itself was originally a stop codon.

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I'm Thylacosmilus.Darwin loves you.