Question

4-3.  To demonstrate an understanding of translation elongation, we’ll start somewhere in the middle of translation of a polypeptide.  At this moment, the entire ribosome (the small and large subunits) is bound to the mRNA, and there is a tRNA bound at the P-site.  Attached to the 3’-end of this tRNA is the start of the polypeptide-

Amino-Met-Leu-Ser-Ala-Phe-tRNA

At this starting point, there is no other tRNA bound to the ribosome, and the next codon is 5’-UGG-3’

When the next tRNA binds to the ribosome, what amino acid will be attached to that tRNA?

And for that next tRNA, write the sequence of the anticodon that is part of that tRNA.

5’ - __ __ __ -3’

And for that tRNA, at which of the tRNA binding sites on the ribosome will it bind?

At the moment that the ribosome forms the next peptide bond, what will the sequence of the newly extended peptide be?  Use the same format that I used when I gave you the initial peptide sequence but include the new amino acid in the sequence.

And at that moment when the ribosome forms the next peptide bond (the one you just showed in the previous part of this question), at which site of the ribosome will the tRNA carrying that peptide be bound?

Eventually, translation will need to end, and the completed polypeptide must be released.  Briefly explain how this translation termination occurs.

Answer 1

When the next tRNA binds to the ribosome, the aminoacid attached to that tRNA will be Tryptophan(Trp).

The sequence of the anticodon that is part of that tRNA is 5' CCA 3'.

That tRNA will bind on the A site of ribosome .

The sequence of the newly extended peptide will be Amino-Met-Leu-Ser-Ala-Phe-Trp-tRNA

At the moment when the ribosome forms the next peptide bond, the tRNA carrying that peptide will be bound to the P site of the ribosome.

Translation termination occurs when the ribosome reaches a stop codon in the A site .Stop codons are UAG,UGA and UAA.Eukaryotic translation termination factor1 (eRF1) recognizes stop codon and Peptidyl-tRNA hydrolysis occurs.