Question

What would happen if in a gene encoding a polypeptide to 5050 amino acid, 25th (UAC) is mutated to UAA?

• A. A polypeptide of $49$ amino acids will be formed
• B. A polypeptide of $25$ amino acids will be formed
• C. A polypeptide of $24$ amino acids will be formed
• D. Two polypeptides of $24$ and $25$ amino acids will be formed

Answer 1

The correct option is C A polypeptide of $24$ amino acids will be formed

Polypeptide chain termination is signalled by three termination codons- UAA (ochre), UAG (amber) and UGA (opal). They do not specify any amino acids, hence called as nonsense codons or stop codon. UAA is a stop codon. So, if in a gene encoding a polypeptide to 50 amino acid, 25th (UAC) is mutated to UAA, then the process will terminate here and a polypeptide of 24 amino acids will be formed.