Medicine & USMLE

Transfer RNA (tRNA)

  1. Messenger RNA (mRNA)
  2. Ribosomal RNA (rRNA)
  3. Transfer RNA (tRNA)
  4. Small Nuclear RNA (snRNA)
  5. MicroRNA (miRNA)
  6. Small Interfering RNA (siRNA)


Transfer RNA, or tRNA, is a class of non-coding RNA responsible for carrying and transferring specific amino acids to create proteins during translation. In order to function during translation, the tRNA must first be activated by loading with an amino acid, through the enzyme aminoacyl-tRNA synthetase. An activated tRNA can then match its anticodon with a complementary codon on mRNA, allowing the transfer of its amino acid to the growing polypeptide chain in the ribosome. tRNA is synthesized by RNA polymerase III  in the nucleus of eukaryotes, and by RNA polymerase in the cytoplasm of prokaryotes.

Key Points

  • Transfer RNA (tRNA)
    • Characteristics
      • Class of non-coding RNA
        • Does not code for proteins
        • Also known as functional RNA
      • Found in eukaryotes and prokaryotes
      • Carries an amino acid
        • 3’ end has a CCA nucleotide sequence where the amino acid binds
      • Contains a 3-nucleotide anticodon
        • Recognizes and pairs with a complementary condon on mRNA during translation in the ribosome
      • Different tRNAs have slightly different structures
        • Important for making sure each tRNA carries the right amino acid
    • Function
      • Transfers a specific amino acid to a growing polypeptide chain
        • The specific amino acid transferred is dictated by mRNA codons that match the tRNA anticodon
        • Occurs during translation in the ribosome
    • Synthesis
      • Eukaryotes
        • Transcribed mostly by RNA Polymerase III in the nucleus
      • Prokaryotes
        • Transcribed by RNA Polymerase in the cytoplasm
    • Activation
      • In order to function during translation, the tRNA must be “loaded” with an amino acid
        • Amino acids must be connected to a specific tRNA molecule to become part of a nascent polypeptide
        • Such tRNA molecules are said to be charged or activated with an amino acid
      • Activation occurs through the enzyme, aminoacyl-tRNA synthetase
        • Only recognizes one amino acid and its tRNAs
        • Once both the amino acid and its tRNA have attached to the synthetase, the enzyme links them together using energy from two adenosine triphosphate (ATP) molecules