Transfer RNA (tRNA)
Transfer RNA (tRNA) is a small non-coding RNA molecule, typically 73–95 nucleotides long, that acts as a physical adaptor during translation by carrying a specific amino acid to the ribosome and recognising the corresponding mRNA codon via its anticodon loop. Each tRNA has a characteristic cloverleaf secondary structure that folds into an L-shaped three-dimensional conformation; the 3' CCA end accepts the amino acid (charged by aminoacyl-tRNA synthetase), while the anticodon loop base-pairs with the mRNA codon in the ribosomal A site. There are at least 61 functional tRNA species in cells (matching all sense codons), and their accurate aminoacylation is essential for translational fidelity.
Structural Regions of a tRNA Molecule and Their Functions
| Region | Structure | Function | Key Feature |
|---|---|---|---|
| Acceptor stem | 7 bp double-stranded | Amino acid attachment at 3' CCA | CCA-3' overhang |
| D loop | Short hairpin with dihydrouridine | tRNA folding and stability | Contains modified bases |
| Anticodon loop | 7-nt loop with anticodon triplet | mRNA codon recognition | Wobble position at 5' of anticodon |
| Variable loop | Variable length | tRNA classification (class I / II) | Size varies 4–21 nt |
| TΨC loop | Short hairpin | Ribosome binding (50S subunit) | Contains pseudouridine |
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Related Terms
Anticodon
An anticodon is a three-nucleotide sequence located in the anticodon loop of a transfer RNA (tRNA) molecule that is complementary and antiparallel to a specific mRNA codon during translation. Base pairing between the codon and anticodon — following Watson-Crick rules (A-U and G-C) and sometimes wobble base pairing at the third position — ensures that the correct amino acid is added to the growing polypeptide chain. Each tRNA carries a specific amino acid at its 3' CCA end that corresponds to its anticodon, making tRNA the physical link between the nucleotide and amino acid languages of the cell.
Translation (biology)
Translation is the process by which a ribosome decodes the nucleotide sequence of a messenger RNA (mRNA) and synthesizes the corresponding sequence of amino acids to produce a polypeptide chain. It occurs in three phases — initiation, elongation, and termination — and takes place at ribosomes in the cytoplasm of both prokaryotes and eukaryotes. The genetic code, read in triplets called codons, determines which amino acid is incorporated at each step, with transfer RNA (tRNA) molecules acting as adaptors between the mRNA codons and the amino acids.
Ribosomal RNA (rRNA)
Ribosomal RNA (rRNA) is the most abundant class of RNA in the cell, constituting approximately 80% of total cellular RNA, and forms the structural and catalytic core of the ribosome by associating with ribosomal proteins. In prokaryotes, the ribosome (70S) contains three rRNA species: 16S rRNA (small 30S subunit), 23S rRNA, and 5S rRNA (large 50S subunit); eukaryotic ribosomes (80S) contain 18S (small 40S subunit), 28S, 5.8S, and 5S rRNAs (large 60S subunit). The 23S/28S rRNA harbours the peptidyl transferase centre — the ribosome's catalytic site for peptide bond formation — making rRNA a ribozyme.
Transfer RNA was named in 1958 by Mahlon Hoagland and Paul Zamecnik following their discovery that small RNA molecules "transfer" amino acids to the growing protein chain. The abbreviation tRNA was established almost immediately and is now universal.