When two languages are different (e.g., English and German) and you want to know what a word in one language means in the other, you may need to consult a foreign-language dictionary or an online translator. Likewise, a “translator” is required to convert the information in mRNA (a language composed of a sequence of nucleotides) into the language of protein (consisting of a sequence of amino acids). In biology, that translator is a special kind of RNA molecule called transfer RNA (tRNA). To ensure accurate translation—that is, to ensure that the protein made is the one specified by the mRNA—the tRNAs must (1) read each codon correctly, and (2) fetch the amino acids corresponding to each codon and deliver them to the ribosome.

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Once the tRNAs “decode” the mRNA and deliver the appropriate amino acids, components of the ribosome catalyze the formation of peptide bonds between amino acids. Let’s now look at how the tRNAs read codons and get the appropriate amino acids into the ribosome.