Diagram depicting the central dogma of biology. Stretches of DNA (commonly called genes) are read by the cellular machinery to produce a matching molecule called RNA. DNA is composed of 4 bases (designated by A, T, C, or G). RNA is also composed of 4 bases but the T is replaced with a U. Every 3 bases in the RNA (called a codon) codes for 1 of 20 different amino acids. Proteins are made by stitching together the correct order of amino acids specified by the RNA. This elegant system is virtually the same for all living things. Click on 'Codon Table' to see the actual code of life. It's amazing!