TransferRNA

Transfer RNA (tRNA) are small RNA molecules that serve as adapters in protein synthesis, translating genetic information from mRNA into a sequence of amino acids. Each tRNA carries a specific amino acid and contains an anticodon, a three-nucleotide sequence that base pairs with the complementary codon on mRNA. tRNA molecules generally fold into a cloverleaf secondary structure with an acceptor stem, a D loop, an anticodon loop, and a TψC loop; at the 3' end is the CCA sequence, either encoded in the gene or added post-transcriptionally, which serves as the attachment site for the amino acid.

Biogenesis and processing: tRNA genes are transcribed by RNA polymerase III. Pre-tRNAs undergo processing to remove leader and trailer sequences, trim 5' and 3' ends, and, in many species, splice introns. After transcription, a variety of nucleotide modifications occur, improving structure and decoding capability. The CCA terminus may be encoded in the genome or added later by specialized enzymes.

Charging and decoding: aminoacyl-tRNA synthetases attach amino acids to their cognate tRNAs in an ATP-dependent reaction, forming aminoacyl-tRNA. Each synthetase recognizes specific identity elements in the tRNA to ensure correct pairing. The charged tRNA delivers the amino acid to the ribosome, where its anticodon pairs with the mRNA codon at the A site. Wobble base pairing allows some tRNAs to recognize multiple codons for a given amino acid, while proofreading by synthetases (and, in some cases, the ribosome) helps maintain translation fidelity.

Role and distribution: tRNAs are abundant in the cytoplasm and in organelles such as mitochondria; in plants, chloroplasts use their own tRNAs as well. tRNA genes can be organized in clusters, and cells employ multiple isoacceptors and related variants to support efficient and accurate translation.