Animation of Protein Synthesis (Translation) in Prokaryotes.

Summary

This script details the process of translation initiation, elongation, and termination in prokaryotes. It describes how the small ribosomal subunit, with the aid of initiation factors IF1, IF3, and IF2, aligns the mRNA's start codon with the ribosome. The initiator tRNA carrying N-formyl-methionine is positioned, and the large subunit assembles. Elongation involves tRNAs entering the A-site, peptide bond formation, and translocation. Termination occurs upon stop codon recognition by release factors, leading to polypeptide release and ribosome disassembly for another translation cycle.

Takeaways

• 🌟 The initiation of translation in prokaryotes involves the separation of the small and large ribosomal subunits with the help of IF1 and IF3 initiation factors.
• 🔍 The small ribosomal subunit binds to the mRNA at the Shine-Dalgarno sequence, which is crucial for proper alignment of the start codon within the ribosome.
• 🔗 The Shine-Dalgarno sequence pairs with a complementary sequence on the 16S rRNA, ensuring the correct positioning of the start codon.
• 🚀 IF2 brings the initiator tRNA with the amino acid N-formyl-methionine to the complex, initiating the translation process.
• 🧬 The large ribosomal subunit then joins the complex, and all initiation factors are released, setting the stage for the translation elongation.
• 🔄 The ribosome has three sites: A-site for new tRNA, P-site for peptidyl-tRNA carrying the growing polypeptide chain, and E-site for tRNA exit.
• 🔑 The initiator tRNA is positioned in the P-site, which is unconventional and sets the stage for the elongation phase.
• 🔄 During elongation, tRNAs carrying amino acids enter the A-site, where their anticodons are matched against the mRNA codon.
• 🛡️ Incorrect tRNAs are rejected through a proof-reading process, ensuring only correct tRNAs participate in peptide bond formation.
• 🔗 Peptide bonds are formed between adjacent amino acids, and the ribosome moves one codon forward on the mRNA, shifting tRNAs from A-site to P-site and then to E-site.
• 🏁 Translation termination occurs when a stop codon is positioned in the A-site, recognized by a release factor that cleaves the bond between the polypeptide and tRNA, releasing the completed polypeptide.
• 🔄 After termination, the ribosome disassociates into subunits, ready to initiate a new round of translation.

Q & A

What are the two initiation factors that help separate the small ribosomal subunit from the large subunit in prokaryotic translation initiation?

The two initiation factors are IF1 and IF3.

What is the purpose of the Shine-Dalgarno sequence in prokaryotic translation?

The Shine-Dalgarno sequence is a purine-rich region that the small ribosomal subunit binds to, ensuring the start codon is in the correct position within the ribosome.

How does the initiator tRNA with the amino acid N-formyl-methionine get involved in the translation process?

Initiation factor IF2 brings in the initiator tRNA charged with the initiator amino acid N-formyl-methionine.

What are the three sites of the ribosome, and what is the function of each site?

The three sites are the A-site (entry for new tRNA), the P-site (occupied by peptidyl-tRNA carrying the growing polypeptide chain), and the E-site (exit for tRNA after delivering the amino acid).

Where is the initiator tRNA positioned during the initiation of translation?

The initiator tRNA is positioned in the P-site.

What happens during the elongation phase of translation when the correct aminoacyl-tRNA enters the A-site?

A peptide bond is made between the two now-adjacent amino acids, and the tRNA in the P-site releases the amino acids onto the tRNA in the A-site, becoming empty.

How does the ribosome move forward on the mRNA during the elongation phase?

The ribosome moves one triplet forward on the mRNA after the peptide bond is formed and the tRNA in the P-site releases the amino acids.

What is the role of the release factor in the termination of translation?

The release factor recognizes the stop codons in the A-site and catalyzes the cleavage of the bond between the polypeptide and the tRNA, releasing the polypeptide from the ribosome.

What occurs after the termination of translation?

The ribosome disassociates into subunits and is ready for a new round of translation.

Why are tRNAs with incorrect anticodons rejected during the elongation phase?

Incorrect anticodons prevent proper codon-anticodon pairing, which is essential for accurate protein synthesis; thus, they are rejected to ensure fidelity in translation.

How does the ribosome ensure the correct aminoacyl-tRNA is matched with the mRNA codon during elongation?

The ribosome checks the incoming tRNA's anticodon against the mRNA codon in the A-site, rejecting those with incorrect anticodons and accepting the correct ones for peptide bond formation.