Prokaryotic Translation Process

Initiation

• Formation of Initiation Complex
  • Involves:
    • 30S ribosomal subunit
    • Formal methionineal tRNA
    • Messenger RNA (mRNA)
  • The 50S ribosomal subunit joins the complex after initiation by the 30S subunit.
  • Initiation factors are involved (though not shown in the lecture).

Ribosomal Structure

• 70S Ribosome Composition
  • Comprises the 30S and 50S subunits.
• Binding Sites
  • P Site (Peptidyl Site): Initiating tRNA carrying formal methionine binds here.
  • A Site (Acceptor Site): New tRNAs carrying amino acids enter here.
  • E Site (Exit Site): Site where tRNAs are released after their amino acids are used.

Elongation

• tRNA Binding and Protein Synthesis
  • tRNA carrying the next amino acid binds at the A site.
  • Peptide bond forms between the amino acids in the P and A sites.
• Ribosome Movement
  • Advances one codon along the mRNA.
  • tRNA in P site moves to E site and is released.
  • New tRNA with matching anticodon to the next mRNA codon enters the A site.
• Peptide Chain Growth
  • Transfer of growing polypeptide chain from P site tRNA to A site tRNA continues.

Termination

• Stop Codon Recognition
  • Entry of a stop codon into the A site halts elongation.
  • Stop codon does not have a corresponding tRNA.
• Dissociation
  • Ribosome splits into 30S and 50S subunits.
  • mRNA and newly synthesized protein are released.