Most likely, when writing the problem statement, a mistake was made: instead of the word “contains”, one should write “encodes”, because mRNA does not contain, but encodes amino acids.
With this amendment, the solution: each amino acid is encoded by three nucleotides, which are called a triplet, or codon. Therefore, to obtain a chain of 14 amino acids, 14 triplets or 14 * 3 = 42 nucleotides are required.
Answer: the desired strand of messenger RNA must contain at least 42 nucleotides.
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