Question

The pioneer round of translation of an mrna is very important to identify potentially dangerous mrnas if per chance they possess aberrant in frame translational stop codons. their detection leads to rapid degradation through the nmd pathway. what indications would the cell use to signal that an mrna possesses an in frame stop following the pioneering read?

a. the mrna has a shorter poly a tail since it is not being efficiently translated if the cap binding protein is no longer associated with the cap it signals to the cell that the mrna is no longer translatable.
b. a stalled ribosomal complex on the mrna is clearly detectable and since the translational machinery cannot initiate protein synthesis it is recognized as toxic and is degraded by the 26s proteasome.
c. if the mrna contains intron sequences then it is quickly recognized by the ribosomes as being abnornal and is degraded rapidly by the 26s proteasome.
d. mrna species that are still bound by key factors that were not removed in the pioneering round of translation are evidence that the translation machinery dissociated prematurely before reaching the true stop at the end of the transcript

Answer 1

The correct indication for a cell to signal the presence of an in-frame stop codon in mRNA is the persistent binding of key factors indicating premature dissociation of the translation machinery.

Step-by-step explanation:

The cell uses specific indications to signal that an mRNA possesses an in frame stop codon following the pioneering round of translation. The correct indication is 'd': mRNA species that are still bound by key factors, which were not removed in the pioneering round of translation, provide evidence that the translation machinery dissociated prematurely before reaching the true stop codon at the end of the transcript. This can occur if the mRNA has a premature termination codon that triggers the cell's nonsense-mediated decay (NMD) pathway, providing a crucial checkpoint to prevent the synthesis of abnormal proteins that could be harmful. It is not due to a stalled ribosomal complex that would invoke degradation by the 26S proteasome, nor due to the presence of introns, as these are typically removed before the mRNA is translated.