All living organisms are made of deoxyribonucleic acid, (DNA.) It is shaped like a ladder that is twirling around and around, a douple helix. On each rung of the "ladder" there is a combination of two chemicals. In total there are four chemicals: adenine (A), thymine (T), cytosine (C), and guanine (G). Even though there ared only four chemicals, there can be many different combinations because more each chemical can be used more than once. Adenine can only fit on a rung with thymine, and cytosine can only fit on a rung with guanine. This means that if there is adenine on one side there has to be thymine on the other. The backbones of the ladder ared made of sugar and phosphate. The molecule of DNA is very small but is 1 000 000 000 (one billion) times longer than it is wide.
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