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. Identify the mRNA sequence corresponding to the polypeptide sequence Phe-Pro-Lys. Using the genetic code, Phe (Phenylalanine) is coded by UUU or UUC, Pro (Proline) by CCU, CCC, CCA, or CCG, and Lys (Lysine) by AAA or AAG.
2. Since the mRNA sequence must match the codons for Phe-Pro-Lys, the mRNA sequence would be 5'-UUUCCCAAA-3'.
3. To find the DNA template strand, remember that mRNA is synthesized 5' to 3' and is complementary to the DNA template strand. Thus, the template strand must be the reverse complement of the mRNA sequence.
4. Convert the mRNA sequence 5'-UUUCCCAAA-3' to the DNA template strand by replacing U with A and finding the complementary bases: A pairs with T, C pairs with G. This gives us 5'-AAAGGGTTT-3'.
5. Reverse the sequence to match the 5' to 3' orientation of the template strand, resulting in 5'-TTTCCCAAA-3'. This matches option d.

Key Concepts

DNA and RNA Structure

DNA and RNA are nucleic acids composed of nucleotide sequences. DNA is double-stranded and contains the bases adenine (A), thymine (T), cytosine (C), and guanine (G), while RNA is single-stranded and contains uracil (U) instead of thymine. Understanding the structure of these molecules is essential for interpreting how genetic information is transcribed from DNA to mRNA.

Transcription Process

Transcription is the process by which the genetic information in DNA is copied into mRNA. During transcription, RNA polymerase synthesizes a complementary RNA strand from the DNA template strand, following base-pairing rules (A-U and C-G). This process is crucial for producing mRNA that encodes for specific polypeptides, such as the one mentioned in the question.

Codons and Amino Acids

Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids during protein synthesis. The polypeptide sequence Phe-Pro-Lys indicates the amino acids phenylalanine, proline, and lysine, which are encoded by specific codons. Understanding the relationship between codons and their corresponding amino acids is vital for determining the correct nucleotide sequence in the DNA template strand.