Transfer RNA (tRNA) is a class of small, non‑coding RNA molecules that deliver specific amino acids to the ribosome during protein synthesis by matching their anticodon sequences to codons on messenger RNA.
Explanation
tRNAs are typically 70–95 nucleotides long and adopt a cloverleaf secondary structure with four main arms: the acceptor arm, the D arm, the anticodon arm and the TΨC arm. The 3′ end of every tRNA ends in a conserved CCA sequence to which the appropriate amino acid is attached by an aminoacyl‑tRNA synthetase. Each tRNA carries a specific anticodon, a triplet of bases that pairs with the complementary codon on the mRNA during translation. Because the genetic code is degenerate, many amino acids are encoded by multiple codons; cells therefore contain families of isoacceptor tRNAs that carry the same amino acid but recognise different codons. Some anticodons exhibit wobble base pairing, allowing a single tRNA to read more than one codon. tRNAs undergo extensive post‑transcriptional modifications, such as methylation or pseudouridylation, which are important for stability and accurate decoding. In bacteria, tRNA genes are often clustered and transcribed together, whereas eukaryotic genomes contain dispersed nuclear and mitochondrial tRNA genes. Proper charging of tRNAs by their cognate synthetases is essential; misacylation can result in incorporation of incorrect amino acids and has been linked to disease.
Examples and roles
Initiator tRNAMet recognises the start codon AUG and delivers methionine or formyl‑methionine to begin polypeptide synthesis. Elongator tRNAMet decodes internal AUG codons. In mitochondria, a reduced set of tRNAs with relaxed wobble rules decodes the organelle’s streamlined genetic code. Some viruses hijack host tRNAs to prime reverse transcription. In genetic experiments, suppressor tRNAs with altered anticodons have been used to bypass nonsense mutations. Under cellular stress, specific tRNA halves and fragments are produced and participate in signalling pathways. Mutations in human tRNA genes or tRNA‑processing enzymes can lead to disorders such as mitochondrial encephalomyopathy. These examples underscore the central role of tRNAs as adaptors between nucleotide sequences and amino acids.
tRNAs are indispensable components of the translation machinery, ensuring that the genetic information encoded in mRNA is accurately converted into the sequence of amino acids in proteins.
Related Terms: Translation, Aminoacyl-tRNA synthetase, Ribosome, Anticodon, Genetic code.