Which of the following sequences of nucleotides are possible in the template strand of DNA that would code for the polypeptide sequence Phe–Leu–Ile–Val?

• A. 5′–TTG–CTA–CAG–TAG–3′.
• B. 5′–AUG–CTG–CAG–TAT–3′.
• C. 3′–AAA–AAT–ATA–ACA–5′.
• D. 3′–AAA–GAA–TAA–CAA–5′.

Answer: (D)

Verified step by step guidance

1. Understand that the template strand of DNA is complementary to the mRNA strand, which is used to determine the amino acid sequence of a polypeptide.
2. Identify the mRNA codons that code for the amino acids Phe, Leu, Ile, and Val using the codon chart. Phe is coded by UUU or UUC, Leu by UUA, UUG, CUU, CUC, CUA, or CUG, Ile by AUU, AUC, or AUA, and Val by GUU, GUC, GUA, or GUG.
3. Determine the mRNA sequence that would code for the polypeptide sequence Phe–Leu–Ile–Val. For example, one possible mRNA sequence is UUU–UUA–AUU–GUU.
4. Convert the mRNA sequence to the template DNA strand. Remember that the template strand is complementary to the mRNA strand, with A pairing with T, U pairing with A, C pairing with G, and G pairing with C.
5. Using the example mRNA sequence UUU–UUA–AUU–GUU, the complementary template DNA strand would be AAA–AAT–TAA–CAA.