key term - Shine-Dalgarno sequence

Definition

The Shine-Dalgarno sequence is a ribosomal binding site located in bacterial mRNA that is essential for the initiation of translation. This short, conserved nucleotide sequence is recognized by the ribosomal RNA of the 30S ribosomal subunit, ensuring that the ribosome properly aligns with the start codon of the mRNA. Its proper functioning is crucial for the accurate synthesis of proteins in prokaryotic organisms.

5 Must Know Facts For Your Next Test

1. The Shine-Dalgarno sequence typically consists of a consensus sequence of about six nucleotides, rich in purines, which pairs with a complementary sequence on the 16S rRNA of the ribosome.
2. This sequence plays a vital role in determining the efficiency and accuracy of translation initiation in bacteria, affecting protein expression levels.
3. The distance between the Shine-Dalgarno sequence and the start codon can influence how well the ribosome binds to mRNA, impacting overall protein synthesis.
4. Variations in the Shine-Dalgarno sequence among different bacterial species can lead to differences in translation initiation mechanisms.
5. In eukaryotes, a similar function is carried out by the 5' cap and poly-A tail of mRNA, highlighting key differences in translation initiation between prokaryotes and eukaryotes.

Review Questions

• How does the Shine-Dalgarno sequence contribute to the process of translation initiation in bacteria?
  • The Shine-Dalgarno sequence is critical for translation initiation in bacteria as it serves as a ribosomal binding site. It pairs with the complementary region on the 16S rRNA within the small subunit of the ribosome, positioning the ribosome correctly at the start codon. This ensures that protein synthesis begins accurately and efficiently, highlighting its importance in prokaryotic gene expression.
• Compare and contrast the roles of the Shine-Dalgarno sequence in prokaryotes and eukaryotic mRNA structures.
  • In prokaryotes, the Shine-Dalgarno sequence facilitates ribosome binding directly to mRNA through complementary pairing with ribosomal RNA. In contrast, eukaryotic mRNA relies on a 5' cap and a poly-A tail for ribosome recruitment. While both mechanisms ensure proper translation initiation, they reflect fundamental differences in how prokaryotic and eukaryotic cells manage gene expression and protein synthesis.
• Evaluate how variations in the Shine-Dalgarno sequence among different bacterial species might affect protein synthesis and cellular function.
  • Variations in the Shine-Dalgarno sequence among bacterial species can lead to differing efficiencies of translation initiation. Such differences may result in varied levels of protein expression, which could impact cellular functions and adaptability to environmental changes. For instance, a strong Shine-Dalgarno sequence may lead to high levels of a critical enzyme under specific conditions, while weaker sequences might result in lower expression levels, affecting how well a bacterium can respond to its surroundings or compete with other microorganisms.

Related terms

Ribosome: A complex molecular machine found within all living cells that serves as the site of protein synthesis by translating messenger RNA into polypeptide chains.

mRNA:

Messenger RNA is a type of RNA that carries genetic information from DNA to the ribosome, where it serves as a template for protein synthesis.

Start codon: A specific sequence of nucleotides in mRNA, typically AUG, that signals the beginning of protein synthesis and is recognized by the ribosome.