Question

Assume that the given mRNA (start site is not depicted) is theoretically translated in two reading frames.
Translation starting from the first nucleotide (Reading frame 1)
Translation starting from the second nucleotide (Reading frame 2)

Frame 1: 5'--CUCGCUUUGCCGAUCAAGGGUUA--3'
Frame 2: 5'--GUGGCACUCAGUCCUUAAUGGCG--3'

Answer the following question: How many amino acids will be specified in case (a) and case (b) on translation? Justify your answer.

Hint:

Translation occurs in triplets (codons), and stops when a stop codon (e.g., UAA, UAG, UGA) is encountered.

Answer 1

Case (a) — Frame 1:
Sequence: CUC GCU UUG CCG AUC AAG GGU UA
Codons grouped from the first nucleotide: \[ \text{CUC} \to \text{Leu},\quad \text{GCU} \to \text{Ala},\quad \text{UUG} \to \text{Leu},\quad \text{CCG} \to \text{Pro},\quad \text{AUC} \to \text{Ile},\quad \text{AAG} \to \text{Lys},\quad \text{GGU} \to \text{Gly} \] The final fragment "UA" is incomplete and untranslated.
Total amino acids in case (a): 7 Case (b) — Frame 2: 
Sequence: GUG GCA CUC AGU CCU UAA UGG CG
Codons grouped from the second nucleotide: \[ \text{GUG} \to \text{Val},\quad \text{GCA} \to \text{Ala},\quad \text{CUC} \to \text{Leu},\quad \text{AGU} \to \text{Ser},\quad \text{CCU} \to \text{Pro},\quad \text{UAA} \to \text{Stop} \] Translation stops at UAA; subsequent codons are not translated. 
Total amino acids in case (b): 5