The shape of a DNA molecule is called a double helix, which looks like a twisting ladder. The "rungs" are made from four nitrogenous bases: adenine, thymine, guanine and cytosine. Sugars and phosphate groups are also part of the structure.
DNA molecules contain all the genetic information that is passed down from parents to their offspring. The four bases are arranged in certain ways, and these determine what information is inherited. Adenine is always paired with thymine, while guanine and cytosine always match up to one another. The specific order of these bases along the ladder makes each organism an individual. Most of an organism's DNA is located in the nucleus of its cells.