Outline the events that occur during initiation of translation in E. coli.

Verified step by step guidance

1. Identify the Shine-Dalgarno sequence on the mRNA, which is a purine-rich region located upstream of the start codon (AUG). This sequence helps the ribosome recognize and bind to the mRNA.
2. The small ribosomal subunit (30S) binds to the mRNA at the Shine-Dalgarno sequence with the help of initiation factors (IFs), such as IF-1, IF-2, and IF-3.
3. The initiator tRNA, charged with N-formylmethionine (fMet-tRNA^fMet), pairs with the start codon (AUG) on the mRNA in the P site of the ribosome. This step is facilitated by IF-2, which is bound to GTP.
4. The large ribosomal subunit (50S) associates with the small subunit to form the complete 70S initiation complex. This step is accompanied by the hydrolysis of GTP to GDP, which is catalyzed by IF-2.
5. The initiation factors (IF-1, IF-2, and IF-3) are released, leaving the ribosome ready to proceed with the elongation phase of translation.

Key Concepts

Translation Initiation

Translation initiation is the first step in protein synthesis where the ribosome assembles around the mRNA. In E. coli, this process begins when the small ribosomal subunit binds to the mRNA at the start codon, typically AUG, which codes for methionine. This step is crucial as it sets the reading frame for the ribosome to translate the mRNA into a polypeptide chain.

Shine-Dalgarno Sequence

The Shine-Dalgarno sequence is a ribosomal binding site in bacterial mRNA that is essential for the initiation of translation. It is located upstream of the start codon and helps align the ribosome with the mRNA by base-pairing with a complementary sequence on the 16S rRNA of the small ribosomal subunit. This interaction ensures that translation begins at the correct site.

Initiation Factors

Initiation factors are proteins that facilitate the assembly of the ribosome and the initiation of translation. In E. coli, key initiation factors such as IF1, IF2, and IF3 play roles in stabilizing the binding of the ribosomal subunits to the mRNA and the initiator tRNA. These factors are essential for ensuring the accuracy and efficiency of the translation initiation process.