At the ribosome, the appropriately charged tRNA is paired with a triplet codon on the messenger. The amino acid is polymerized with the growing chain, and the ribosome moves down the messenger by three bases to repeat the process with the next codon. When one of the three "stop" codons is read, the completed polypeptide chain falls away from the ribosome and completes its folding into a functioning protein molecule.

This in broad outline is the machinery by which linear information in a polynucleic acid is translated into three-dimensional information in an enzyme molecule. More details would take us into molecular biology rather than chemistry, and soon would take us to the limits of our present-day knowledge. The information in DNA is sometimes compared with music on a magnetic tape. In principle the music is all there on the isolated tape, but it is inaccessible without a player. The mRNA, tRNA, ribosomes, and various charging and polymerizing enzymes are like the stereo playback set, without which the information is only useless fluctuations along a chain.

Right: Three-dimensional model of DNA. Because of the base-pair connections to the backbone are not exactly 180º apart, the two grooves up the outside of the helix are of unequal width.