tRNA

Overview

•  Structure
  • cloverleaf structure
  • 3′ aminoacyl end = CCA   
    • bound covalently to amino acid (AA)
• Charging 
  • purpose 
    • adds correct AA to correct tRNA
      • each AA has a specific tRNA
      • correct AA is only checked when attachment occurs by aminoacyl-tRNA synthetase to the tRNA
      • thus, if a AA is mischarged, it has no other correction mechanism and will insert for the AA specified by the tRNA anticodon
    • charged tRNA contains the needed energy for the formation of the peptide bond
  • process
    • tRNA + ATP + aa → aa-tRNA + AMP + PP_i
    • catalyzed by aminoacyl-tRNA synthetase
  • inhibited by tetracyclines
• Wobble 
  • first 2 nucleotide positions provide specificity for an individual amino acid
    • e.g., mRNA triplets CUU, CUC, CUA, CUG all code for Leu
  • genetic code is degenerate
    • all amino acids except for one have more than one codon
  • explains silent mutations
• mutation from CUU to CUC would not alter the protein