Question

How many amino aicds will be coded by the mRNA sequence?

$5^{\prime }CCCUCAUAGUCAUAC{3}^{\prime }$ if a adenosine residue is inserted after ${12}^{th}$ nucleotide?

• A. Five amino acids
• B. Six amino acids
• C. Two amino acids
• D. Three amino acids

Answer 1

Answer: (C)

Two amino acids

In the given mRNA strand, the 7${}^{th}$, 8${}^{th}$ and 9${}^{th}$ position is marked by UAG codon which is a stop codon that stops the amino acid polymerization to a polypeptide. Therefore, the addition of adenosine residue after the 12${}^{th}$ nucleotide will not make any reading shift before it. Hence, the given mRNA will be translated only till 9${}^{th}$ nucleotide and accordingly, only two amino acids will be coded.

Hence, the correct answer is 'Two amino acids'.