DNA is made from small units called nucleotides. Each nucleotide has three parts: one sugar, one phosphate group and one base. The base is attached to the sugar.
The sugar and the phosphate group are the same in every nucleotide. What changes is the base. There are four different bases, adenine (A), thymine (T), guanine (G) and cytosine (C), so there are four different nucleotides.
The nucleotides join in a chain, so a strand of 10 nucleotides has 10 sugars, 10 phosphate groups and 10 bases. The order of the bases along a strand is the code that carries the genetic information.
