The next great discovery in genetics, after the structure of the DNA molecule, was the way in which the sequence of DNA bases on the chain carry the information on how to make proteins. The cell first makes a copy of the DNA instructions. The DNA instructions contain a region which controls how often a copy is made. The copy is made of a different type of nucleic acid called RNA.
The RNA copy is moved to the protein making machinery in the cell which is called the "ribosome". Every set of three RNA bases in a row control which amino acid is to be added to a growing protein molecule. A special three base code (usually ATG) tells the ribosome where the instructions on how to make the protein begin in the sequence. The copy of the DNA chain passes through this protein making machinery like a tape through a tape player. The ribosome, however, produces protein instead of sound!