key term - Shine-dalgarno sequence

Definition

The shine-dalgarno sequence is a ribosomal binding site in bacterial mRNA, crucial for the initiation of translation. It is typically located just upstream of the start codon and complements the 16S rRNA of the small ribosomal subunit, helping to ensure proper alignment of the mRNA with the ribosome. This sequence plays a key role in regulating gene expression at the translational level by influencing the efficiency of protein synthesis.

5 Must Know Facts For Your Next Test

1. The shine-dalgarno sequence usually consists of a consensus sequence that is rich in purines, allowing it to base pair effectively with the complementary sequence in the ribosomal RNA.
2. Its position relative to the start codon is critical; variations can affect how efficiently ribosomes can bind and initiate translation.
3. Different bacterial species can have variations in their shine-dalgarno sequences, impacting the regulation of gene expression in response to environmental changes.
4. The strength of the shine-dalgarno interaction influences how often a given mRNA is translated into protein, serving as a regulatory mechanism for gene expression.
5. Mutations in the shine-dalgarno sequence can lead to defects in protein synthesis, which can affect cellular function and organismal health.

Review Questions

• How does the shine-dalgarno sequence contribute to the efficiency of translation initiation in bacteria?
  • The shine-dalgarno sequence enhances translation initiation by providing a specific binding site for the ribosome. This sequence pairs with the 16S rRNA of the small ribosomal subunit, ensuring that the ribosome is properly positioned at the start codon. By facilitating this precise alignment, it increases the likelihood that translation will begin efficiently, directly impacting protein production levels.
• Discuss how variations in shine-dalgarno sequences among different bacterial species can affect gene expression.
  • Variations in shine-dalgarno sequences across bacterial species can lead to differences in translation efficiency. Each species may have adapted its sequences to optimize ribosomal binding under specific environmental conditions, thus influencing how often certain proteins are synthesized. These differences allow bacteria to regulate their gene expression dynamically based on their surroundings and metabolic needs.
• Evaluate the potential consequences of mutations in the shine-dalgarno sequence on bacterial protein synthesis and overall cell function.
  • Mutations in the shine-dalgarno sequence can disrupt its ability to interact with ribosomal RNA, leading to inefficient or failed translation initiation. This can result in reduced levels of essential proteins, affecting metabolic pathways and cellular processes. In some cases, such mutations might even lead to cell death or reduced viability due to insufficient production of critical proteins necessary for growth and survival.

Related terms

Ribosome: A molecular machine composed of RNA and proteins that synthesizes proteins by translating messenger RNA into polypeptide chains.

mRNA:

Messenger RNA, a type of RNA that carries genetic information from DNA to the ribosome for protein synthesis.

Translation initiation: The first phase of translation where the ribosome assembles around the start codon of the mRNA and begins synthesizing a protein.