Using Figure 17.6, identify a 5′→3′ sequence of nucleotides in the DNA template strand for an mRNA coding for the polypeptide sequence Phe-Pro-Lys.





a. 5′-UUUCCCAAA-3′
b. 5′-GAACCCCTT-3′
c. 5′-CTTCGGGAA-3′
d. 5′-AAACCCUUU-3′

Verified step by step guidance

1. Understand that the problem requires identifying the DNA template strand sequence that would result in an mRNA coding for the polypeptide sequence Phe-Pro-Lys.
2. Recall that the mRNA sequence is complementary to the DNA template strand and is synthesized in the 5′ to 3′ direction. The DNA template strand is read in the 3′ to 5′ direction.
3. Identify the mRNA codons for the amino acids: Phe (Phenylalanine) is coded by UUU or UUC, Pro (Proline) is coded by CCU, CCC, CCA, or CCG, and Lys (Lysine) is coded by AAA or AAG.
4. Construct the mRNA sequence from the given polypeptide sequence: Phe-Pro-Lys could be coded by the mRNA sequence 5′-UUUCCCAAA-3′.
5. Determine the complementary DNA template strand sequence by replacing each mRNA nucleotide with its complementary DNA base: A (adenine) with T (thymine), U (uracil) with A, C (cytosine) with G (guanine), and G with C. The complementary DNA sequence for the mRNA 5′-UUUCCCAAA-3′ is 3′-AAAGGGTTT-5′, which corresponds to the 5′-TTTGGGAAA-3′ when written in the 5′ to 3′ direction.

Key Concepts

DNA Template Strand

The DNA template strand is the sequence of DNA that is used as a template for RNA synthesis during transcription. It is complementary to the mRNA strand, meaning that the mRNA is synthesized in the 5′ to 3′ direction using the template strand's 3′ to 5′ sequence. Understanding this concept is crucial for determining the correct nucleotide sequence that codes for a specific polypeptide.

Codon and Anticodon

A codon is a sequence of three nucleotides on mRNA that corresponds to a specific amino acid or stop signal during protein synthesis. The anticodon is the complementary sequence on tRNA that pairs with the mRNA codon during translation. Recognizing codon sequences for amino acids like Phe, Pro, and Lys is essential for identifying the correct DNA template sequence.

Transcription and Translation

Transcription is the process of synthesizing mRNA from a DNA template, while translation is the process of decoding mRNA to build a polypeptide chain. These processes involve converting nucleotide sequences into amino acid sequences, which is fundamental for understanding how a DNA sequence can code for a specific polypeptide sequence like Phe-Pro-Lys.