While DNA (Deoxyribonucleic Acid) is the building block of very complex organisms, such as humans, its basic structure is fairly simple. DNA is made up of three different molecules: a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogen base. These three molecules together compose what is called a nucleotide. Four different nucleotides make up all DNA, which only differ by their nitrogen base group. Thus, the nucleotides are named for their nitrogen group. The four different nucleotides are adenine (A), guanine (G), cytosine (C), and thymine (T).

These nucleotides arrange themselves in an interesting shape called a double helix. This looks like a ladder, where the two sides are coiled around one another. The sides of the ladder are formed by the sugar and phosphate groups of the nucleotides, which bond together linearly. The nitrogen base group sticks out from this chain, and bonds together with a base of another string of nucleotides