DNA—Deoxyribose Nucleic Acid—is the most important hereditary molecule of every living thing. It often has been called the “code of life,” and Francis Collins, the director of the Human Genome Project for many years, even called it the “language of God.” This comparison to a “code” or “language” is based on the amazing structure of DNA: it is made up of a string or chain of smaller units – smaller molecules – that act like a precise sequence of letters spelling out a message. The exact order of those chemical units conveys true “information,” and this information is extremely vital for the health of that living organism. In this unit, we will focus on two aspects of DNA: first, we will see how DNA is stored within the cell. Then, we will take a closer look at the way it is arranged to form individual messages.