Chain Elongation in Prokaryotic Protein Synthesis

Chain elongation is the central phase of protein synthesis in prokaryotes, occurring on the ribosome after translation initiation. During elongation, amino acids are added sequentially to the growing polypeptide chain according to the mRNA template. Key features and steps include:

• Ribosome Structure: The ribosome has three critical sites:
  
  • A site (Aminoacyl site): Entry point for incoming tRNAs carrying amino acids.
  • P site (Peptidyl site): Holds the tRNA attached to the growing polypeptide chain.
  • E site (Exit site): Where empty tRNAs leave the ribosome.
     
• tRNA Delivery: Aminoacyl-tRNA binds to the A site, guided by its anticodon matching the mRNA codon. Elongation Factor Tu (EF-Tu), powered by GTP, ensures accurate delivery.
   
• Peptide Bond Formation: The ribosome’s peptidyl transferase activity catalyzes the formation of a peptide bond between the amino acid in the A site and the polypeptide attached to the tRNA in the P site.
   
• Translocation: The ribosome moves one codon along the mRNA, shifting the tRNA from A → P and P → E. Elongation Factor G (EF-G), using GTP, facilitates this movement. The empty tRNA exits from the E site, making space for the next aminoacyl-tRNA.
   
• Cycle Continuation: This process repeats, elongating the polypeptide chain with high fidelity, codon by codon.
   
• Termination: Elongation continues until a stop codon enters the A site, signaling release factors to end translation and free the completed protein.
   

This orchestrated cycle ensures that proteins are synthesized accurately and efficiently, reflecting the remarkable precision of prokaryotic translation machinery.