In the genetic code, how many mRNA codons specify a single amino acid during translation?

• A. Two codons (a doublet of nucleotides) specify one amino acid.
• B. One codon specifies three amino acids because codons are read in overlapping frames.
• C. Three codons specify one amino acid because each nucleotide corresponds to one amino acid.
• D. One codon (a triplet of nucleotides) specifies one amino acid.

Answer: (D)

Verified step by step guidance

1. Understand that the genetic code is read in units called codons during translation, where each codon corresponds to a specific amino acid.
2. Recall that a codon consists of three nucleotides (a triplet), not one or two, which together specify a single amino acid.
3. Recognize that codons are read in a non-overlapping, sequential manner along the mRNA strand, meaning each set of three nucleotides is distinct and does not overlap with adjacent codons.
4. Note that the idea of overlapping frames or doublets is incorrect because it would cause ambiguity in the genetic code and disrupt proper protein synthesis.
5. Conclude that each codon, composed of three nucleotides, uniquely specifies one amino acid during translation.