A DNA sequence encoding a five-amino acid polypeptide is given below.
...ACGGCAAGATCCCACCCTAATCAGACCGTACCATTCACCTCCT...
...TGCCGTTCTAGGGTGGGATTAGTCTGGCATGGTAAGTGGAGGA...
Assuming the sequence above is a bacterial gene, identify the region encoding the Shine–Dalgarno sequence.

Verified step by step guidance

1. Identify the Shine–Dalgarno sequence, which is a ribosome-binding site in bacterial mRNA. It is typically located upstream of the start codon (AUG) and is rich in purines (adenine and guanine).
2. Examine the given DNA sequence for regions that could correspond to the Shine–Dalgarno sequence. Remember that the Shine–Dalgarno sequence is complementary to a region of the 16S rRNA and often contains the consensus sequence 5'-AGGAGG-3'.
3. Determine the mRNA sequence by transcribing the given DNA sequence. Use the coding strand (5' to 3') to generate the mRNA sequence, replacing thymine (T) with uracil (U).
4. Search the mRNA sequence for a region upstream of the start codon (AUG) that matches or closely resembles the Shine–Dalgarno consensus sequence.
5. Once the Shine–Dalgarno sequence is identified, note its position relative to the start codon and confirm that it is located within the typical range (approximately 3-10 nucleotides upstream of the AUG codon).

Key Concepts

Shine-Dalgarno Sequence

The Shine-Dalgarno sequence is a ribosomal binding site in bacterial mRNA, crucial for initiating translation. It is typically located upstream of the start codon and is complementary to a sequence in the 16S rRNA of the ribosome, facilitating the assembly of the ribosome on the mRNA. This sequence ensures that the ribosome correctly identifies the start site for protein synthesis.

Translation Initiation

Translation initiation is the first step in protein synthesis, where the ribosome assembles around the mRNA. In bacteria, this process begins when the ribosome binds to the Shine-Dalgarno sequence, positioning the start codon in the ribosomal P site. This step is essential for the accurate translation of the genetic code into a polypeptide chain.

Bacterial Gene Structure

Bacterial genes are typically organized in operons, which are clusters of genes transcribed as a single mRNA molecule. The structure includes regulatory sequences, such as promoters and the Shine-Dalgarno sequence, that control gene expression. Understanding this organization is vital for identifying functional elements within a given DNA sequence.