Translation (biology)

Translation is the stage of gene expression in which the genetic message carried by messenger RNA (mRNA) is decoded to build a protein. It follows transcription — the copying of DNA into mRNA — and completes the flow of the central dogma: DNA to RNA to protein. The name is apt: the cell translates from the language of nucleotides into the language of amino acids.

The work happens at the ribosome, which reads the mRNA three nucleotides at a time. Each triplet, or codon, specifies one amino acid according to the genetic code. Transfer RNA (tRNA) molecules serve as adapters: each carries a specific amino acid and bears an anticodon that base-pairs with the matching codon. As the ribosome moves along the mRNA, tRNAs deliver amino acids in order, and the growing chain is linked together by peptide bonds.

Translation proceeds in three phases. In initiation, the ribosome assembles on the mRNA at the start codon (AUG, encoding methionine). In elongation, tRNAs cycle through the ribosome's A, P, and E sites as the polypeptide grows. In termination, a stop codon (UAA, UAG, or UGA) is reached, release factors free the finished protein, and the ribosome disassembles. In eukaryotes, translation occurs in the cytoplasm on free ribosomes or the rough endoplasmic reticulum; in bacteria it can begin while the mRNA is still being transcribed, and differences between bacterial and human ribosomes make translation a major antibiotic target.

Translation is fundamental exam material: the USMLE Step 1 tests its machinery, phases, and the antibiotics that inhibit it, while the MCAT tests translation within the transmission of genetic information from gene to protein.