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Introduction: What Is DNA?

A schematic shows three double-stranded DNA molecules against a white background. The sugar-phosphate backbone of the molecule in the middle of the frame is represented as a segmented grey cylinder coiled into a double helical shape. Base pairs are represented as twisted rectangular prisms connecting the two strands and resemble rungs on a ladder, each half of the rungs being a different color, either blue-orange or green-red. The different colors represent the different nucleotide bases that make up each pair. DNA molecules on the lower left and upper right resemble the molecule shown in the center, but are shown only in grey scale.
Deoxyribonucleic acid, more commonly known as DNA, is a complex molecule that contains all of the information necessary to build and maintain an organism. All living things have DNA within their cells. In fact, nearly every cell in a multicellular organism possesses the full set of DNA required for that organism.

However, DNA does more than specify the structure and function of living things — it also serves as the primary unit of heredity in organisms of all types. In other words, whenever organisms reproduce, a portion of their DNA is passed along to their offspring. This transmission of all or part of an organism's DNA helps ensure a certain level of continuity from one generation to the next, while still allowing for slight changes that contribute to the diversity of life.

But what, exactly, is DNA? What smaller elements make up this complex molecule, how are these elements arranged, and how is information extracted from them? This unit answers each of these questions, and it also provides a basic overview of the process of DNA discovery.

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