The mRNA codon for the amino acid tyrosine is UAU. What is the corresponding DNA triplet for tyrosine?

The mRNA codon for the amino acid tyrosine is UAU. What is the corresponding DNA triplet for tyrosine?

• A. TAT
• B. ATA
• C. ATT
• D. UAU

Answer: (B)

The main idea is that mRNA codons pair with a DNA template strand during transcription, so the DNA sequence that serves as the template is complementary to the mRNA codon. For the mRNA codon UAU, pair each base with its DNA template complement: U pairs with A, A pairs with T, and U again pairs with A. Reading that in the sequence of the template strand gives ATA. So the DNA triplet that would be used as the template to produce this mRNA codon is ATA. (If you were asked for the DNA coding strand, you would replace U with T to get TAT, but the template answer is ATA.) Tyrosine can also be coded by UAC in mRNA, which would correspond to a different template triplet, illustrating the same complementary principle.

The main idea is that mRNA codons pair with a DNA template strand during transcription, so the DNA sequence that serves as the template is complementary to the mRNA codon.

For the mRNA codon UAU, pair each base with its DNA template complement: U pairs with A, A pairs with T, and U again pairs with A. Reading that in the sequence of the template strand gives ATA. So the DNA triplet that would be used as the template to produce this mRNA codon is ATA. (If you were asked for the DNA coding strand, you would replace U with T to get TAT, but the template answer is ATA.) Tyrosine can also be coded by UAC in mRNA, which would correspond to a different template triplet, illustrating the same complementary principle.