The codons AAA, CCC, GGG, and UUU specify the amino acids lysine, proline, glycine, and phenylalanine, respectively. If the base sequence 5′-CCCAAATTTGGG-3′ is present in the coding strand of a stretch of DNA, what polypeptide sequence would be encoded by the corresponding template strand?

• A. lys-pro-gly-phe
• B. gly-phe-lys-pro
• C. phe-gly-pro-lys
• D. pro-lys-phe-gly

Answer: (D)

Verified step by step guidance

1. Understand the relationship between the coding strand and the template strand of DNA. The coding strand is the same as the mRNA sequence except that thymine (T) in DNA is replaced by uracil (U) in RNA.
2. Identify the sequence of the template strand. The template strand is complementary to the coding strand. For the coding strand 5′-CCCAAATTTGGG-3′, the template strand will be 3′-GGGTTTAAACCC-5′.
3. Transcribe the template strand into mRNA. The mRNA is complementary to the template strand and identical to the coding strand (except for U replacing T). The mRNA sequence will be 5′-CCCAAAGGGUUU-3′.
4. Divide the mRNA sequence into codons. Codons are groups of three nucleotides. The mRNA sequence 5′-CCCAAAGGGUUU-3′ can be divided into the codons: CCC, AAA, GGG, UUU.
5. Translate the mRNA codons into amino acids using the genetic code. The codons CCC, AAA, GGG, and UUU correspond to the amino acids proline, lysine, glycine, and phenylalanine, respectively. Therefore, the polypeptide sequence encoded is pro-lys-phe-gly.