Have you ever wondered how a seed becomes a tree or how a fertilized egg becomes a human? Have you ever wondered how you inherited your traits? The answers involve the information found in DNA.

Nearly all cells have DNA, complex molecules that resemble long twisted ladders. In the human genome, or our complete set of DNA, the ladders have approximately three billion chemical “rungs.” Scientists call these rungs base pairs because each rung is made up of two chemical substances, of which there are four altogether. Using the first letter of each, these substances are abbreviated A, C, G, and T —a simple, four-letter alphabet, as it were. In 1957, Crick proposed that it is the linear sequence of the chemical rungs that forms coded instructions. In the 1960’s, that code began to be understood.

Information, whether in the form of pictures, sounds, or words, can be stored and processed in many ways. Computers, for example, do this all digitally. Living cells store and process information chemically, DNA being the key compound. DNA is passed on when cells divide and organisms reproduce —abilities that are considered defining characteristics of life.

How do cells use information? Think of DNA as a collection of recipes, each one involving step-by-step processes, with each step carefully scripted in precise terms. But instead of the end result being a cake or a cookie, it might be a cabbage or a cow. In living cells, of course, the processes are fully automated, adding yet another layer of complexity and sophistication.

The information in a bacterial cell would fill a 1,000-page book

Genetic information is stored until it is needed, perhaps to replace worn out or diseased cells with healthy new ones or to pass on traits to offspring. How much information does DNA hold? Consider one of the smallest organisms, bacteria. German scientist Bernd-Olaf Küppers stated: “Carried over to the realm of human language, the molecular text describing the construction of a bacterial cell would be about the size of a thousand-page book.” For good reason, chemistry professor David Deamer wrote: “One is struck by the complexity of even the simplest form of life.” How does the genome of a human compare? “[It] would fill a library of several thousand volumes,” says Küppers.