A mRNA has 69 nucleotides which includes the stop codon. Calculate the number of amino acids present in the polypeptide chain.

3 nucleotides form 1 codon. 1 codon codes for 1 amino acid. The stop codon do not code for any amino acid. Therefore no. of codons in a 69-nucleotide mRNA is 69/3= 23. But it contains 1 stop codon. Therefore, no. of amino acids present in polypeptide chain is 23-1=22 amino acids