• It refers to polymerization of amino acids to form a polypeptide.
  • The number and sequence of amino acids are defined by the sequence of bases in the mRNA.
  • The amino acids are joined by peptide bond.
  • Amino acids are activated in the presence of ATP and linked to their specific tRNA is called charging of tRNA or aminoacylation of tRNA.
  • Ribosome is the cellular factory for protein synthesis.
  • Ribosome consists of structural rRNA and 80 different proteins.
  • In inactive state ribosome(70S) present in two subunits:-
    • A large sub unit 50S.
    • A small sub unit 30S.



  • The process of translation or protein synthesis begins with attachment of mRNA with small subunit of ribosome.
  • The ribosome binds to the mRNA at the start codon (AUG).
  • AUG is recognized by the initiator tRNA.


  • Larger subunit attached with the initiation complex.
  • Larger subunit has two site ‘A’ site and ‘P’ site.
  • Initiator tRNA accommodated in ‘P’ site of large subunit, the subsequent amino-acyl-tRNA enters into the ‘A’ site.
  • The sub subsequent tRNA selected according to the codon of the mRNA.
  • Codon of mRNA and anticodon of tRNA are complementary to each other.
  • Formation of peptide bond between two amino acids of ‘P’ and ‘A’ site, catalyzed by ribozyme, (23S rRNA in bacteria)
  • The moves from codon to codon along the mRNA called translocation.


  • Elongation continues until a stop codon arrives at ‘P’ site.
  • There is no tRNA for stop codon.
  • release factor binds to the stop codon.
  • Further shifting of ribosome leads to separation of polypeptide.
  • An mRNA also has some additional sequences that are not translated called untranslated regions (UTR).

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