A protein is encoded by a piece of mRNA 660 nucleotides long. What is the maximum number of amino acids in the protein?

A protein is encoded by a piece of mRNA 660 nucleotides long. What is the maximum number of amino acids in the protein?

• A. 180
• B. 220
• C. 330
• D. 660

Answer: (B)

Genes are read in codons of three nucleotides, and each codon specifies one amino acid (with stop codons signaling termination). Therefore, the maximum number of amino acids that can be encoded by an mRNA segment is the total nucleotides divided by 3, rounding down if needed. For 660 nucleotides, that’s 660 ÷ 3 = 220 codons that could code amino acids. The protein could reach 220 amino acids in the maximum-case scenario where no stop codon occurs within the coding region. (If a stop codon were present, the count would drop by one, but the question asks for the maximum, so 220 is the best answer.)

Genes are read in codons of three nucleotides, and each codon specifies one amino acid (with stop codons signaling termination). Therefore, the maximum number of amino acids that can be encoded by an mRNA segment is the total nucleotides divided by 3, rounding down if needed. For 660 nucleotides, that’s 660 ÷ 3 = 220 codons that could code amino acids. The protein could reach 220 amino acids in the maximum-case scenario where no stop codon occurs within the coding region. (If a stop codon were present, the count would drop by one, but the question asks for the maximum, so 220 is the best answer.)