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#UGA codon

3 public questions tagged with this topic.

Eukaryotes gene regulation

UGA codon normally codes for

Standard genetic code assigns three codons to termination: UAA ochre, UAG amber, UGA opal, recognized by release factor RF2 in bacteria and eRF1 in eukaryotes triggering peptidyl-tRNA hydrolysis and ribosome dissociation. Sixty-one codons encode amino acids, three terminate. In most transcripts UGA functions as stop, least frequent in highly expressed bacterial genes. Its dual use for selenocysteine illustrates conditional reassignment where mRNA context redefines meaning, yet default decoding terminates protein synthesis. This plasticity demonstrates evolutionary flexibility where infrequent stop codon allows occasional recoding without globally disrupting proteome termination fidelity essential for accurate translation.

Ref: NCBI Bookshelf, Molecular Biology: Genetic Code – Stop Codons and UGA Function

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Eukaryotes gene regulation

Selenocysteine is incorporated during

Unlike typical post-translational modifications such as phosphorylation or acetylation, selenocysteine incorporation occurs concurrently with polypeptide elongation at ribosome exit tunnel. UGA normally terminates translation via release factors, yet selenoprotein mRNAs carry downstream SECIS element recruiting SBP2 and EFSec. Sec-tRNASec delivered to ribosomal A-site pairs with UGA retained within coding frame, peptide bond formation directly inserts selenocysteine into nascent chain before chain release. This cotranslational recoding requires specialized tRNA, elongation factor, and SECIS-binding proteins, blurring distinction between regulatory signal and coding sequence. Thus selenocysteine becomes primary sequence component, not added after folding.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 5: Translation Exception – Co-translational Sec Insertion

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Amino Acids Structure

Which amino acid is encoded by the UGA stop codon but incorporated in certain proteins?

Selenocysteine is the scientifically accurate answer to this question. Within the study of Amino_Acids_Structure, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Selenocysteine directly address what is being asked. Among the other options, Pyrrolysine, Ornithine, and Citrulline do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Campbell Biology, Urry et al., 12th Ed.

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