Translation In translation, a cell reads an mRNA message and assembles a polypeptide accordingly. Here is how translation occurs. As an mRNA strand slides through a ribosome, triplets of RNA bases spell out the amino acid sequence of a polypeptide. It is the job of transfer RNA molecules to match RNA bases with the correct amino acids. Let's go through the functions of each component. Messenger RNA (or mRNA) Messenger RNA (mRNA) carries the genetic message from the nucleus to the cytoplasm. Codons (triplets of RNA bases) spell out the amino acid sequence of a polypeptide, from a start codon near the 5 prime end of the mRNA to a stop codon near the 3 prime end. The portion of the mRNA that actually codes for a polypeptide is called the coding segment. Amino Acids There are twenty kinds of amino acids. They are strung together in a certain sequence, as specified in the mRNA message, to make each kind of polypeptide. The polypeptide folds in a certain way, and it may be modified or linked to other polypeptides to make a functional protein.