Translation termination | translation in prokaryotes lecture 5

Summary

This video explains the termination of protein synthesis in prokaryotes, focusing on the role of release factors. The process begins when the ribosome encounters a stop codon, bringing in release factor 1 (RF1), which mimics a tRNA to release the polypeptide chain. RF2 further aids in the release of RF1, and the ribosomal subunits dissociate. Elongation factor G (EF-G) and ribosome release factor (RRF) facilitate this dissociation, while initiation factor 3 (IF3) prevents reattachment of the ribosomal subunits. The video highlights the importance of protein synthesis in cellular functions and its essential role in life processes.

Takeaways

• 😀 Protein synthesis in prokaryotes involves initiation, elongation, and termination stages.
• 😀 Termination of protein synthesis occurs when a stop codon is encountered by the ribosome.
• 😀 Instead of bringing in tRNA, a release factor (RF1) is brought to the stop codon during termination.
• 😀 Release factor 1 mimics tRNA in structure and helps cleave the peptide bond, releasing the synthesized protein.
• 😀 After release factor 1 cleaves the peptide chain, release factor 2 is brought in to help release RF1.
• 😀 Release factor 2 uses GTP to bind with the ribosomal subunit, and this energy helps release RF1 from the ribosome.
• 😀 Ribosome release factor (RRF) and elongation factor G (EF-G) also play key roles in the final steps of termination.
• 😀 GTP hydrolysis by EF-G drives the translocation of the ribosomal subunits, which causes the release of tRNA from the ribosome.
• 😀 The ribosome dissociates into its 30S and 50S subunits after the completion of translation, with the help of initiation factor 3 (IF3).
• 😀 IF3 prevents the 50S subunit from attaching prematurely, aiding in the dissociation of the ribosome after translation.
• 😀 Once all factors are released, including mRNA, the ribosome is completely dissociated, marking the end of protein synthesis.

Q & A

What triggers the termination of protein synthesis in prokaryotes?

Termination of protein synthesis occurs when the ribosome encounters a stop codon on the mRNA, signaling the end of translation.

How does the role of tRNA change during termination compared to elongation?

During elongation, tRNA brings amino acids based on the codon sequence. In termination, instead of a tRNA, a release factor (RF) mimics tRNA to bind to the stop codon and release the completed polypeptide.

What is the function of Release Factor 1 (RF1) in termination?

RF1 mimics tRNA and binds to the stop codon in the A site. It has two domains: one that pairs with the stop codon and another with exonuclease activity, which breaks the peptide bond to release the polypeptide chain.

What happens to the polypeptide after RF1 cleaves the peptide bond?

Once RF1 cleaves the peptide bond, the polypeptide is released from the ribosome and is free to fold into its functional form.

What is the role of Release Factor 2 (RF2) during termination?

RF2 comes in after RF1 is released. It binds to the ribosome with GTP and helps release RF1 by hydrolyzing GTP, leading to the dissociation of both release factors.

How does GTP play a role in the termination process?

GTP provides the energy necessary for several steps in termination, including the binding and release of release factors and the dissociation of ribosomal subunits.

What is the function of Ribosome Release Factor (RRF) in the termination process?

RRF helps in the final dissociation of the ribosomal subunits after the polypeptide chain is released. It works alongside IF3 to release mRNA and separate the 50S and 30S subunits.

Why does IF3 bind to the 30S ribosomal subunit during termination?

IF3 binds to the 30S subunit to prevent it from reattaching to the 50S subunit, aiding in the dissociation of the ribosome and the release of mRNA.

What happens after the hydrolysis of GTP by elongation factor G (EF-G)?

After GTP hydrolysis by EF-G, energy is released to drive the translocation of the ribosomal complex, helping to move the ribosome along the mRNA and complete the termination process.

What is the ultimate outcome of the termination process in protein synthesis?

The ultimate outcome is the dissociation of the ribosomal subunits (30S and 50S), the release of mRNA, and the separation of various factors, marking the end of protein synthesis.