An mRNA runs from a start codon to a stop codon and contains 450 nucleotides, including the stop codon. How many amino acids are in the polypeptide? (The stop codon does not code for an amino acid.)
Answer and explanation
Correct answer: B. 149
- Step 1: Each codon has 3 nucleotides: 450/3 = 150 codons.
- Step 2: The last is the stop codon, so there are 150-1=149 amino acids.
Answer
149.
Why not the others: 150: the stop codon was counted as an amino acid. 450: the number of nucleotides was used. 148: one codon too many was subtracted.
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