Sequence of amino acids, in a polypeptide chain of protein molecule, corresponds to the sequence of nucleotides on mRNA for that protein. If the reading frame of mRNA for a human protein is 993 nucleotides, including a stop codon at the end, how many amino acids would be incorporated in the polypeptide chain?
Correct answer: B. 330
- A. 93
- B. 330
- C. 331
- D. 993
Explanation
Codon consists of three nucleotides, and each codon corresponds to a single amino acid. A stop codon, however, does NOT code for an amino acid; they signal the end or termination of the polypeptide chain. Hence, out of the 993 nucleotides, the last three correspond to a stop codon and hence 990 nucleotides are to be considered. 990 nucleotides correspond to 330 codons (990 divided by 3), and since each codon codes for a single amino acid, 330 codons will code for 330 amino acids, hence, the answer is B.
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