DNA (deoxyribonucleic acid) is the genetic material found in the nucleus of a cell. It carries the instructions a cell uses to make proteins. DNA is a polymer, which means it is a very long molecule built from many small repeating units joined together in a chain.
The repeating units in DNA are called nucleotides. Each nucleotide contains three parts: a sugar, a phosphate group and one base. There are four different bases, called adenine (A), thymine (T), cytosine (C) and guanine (G). The order of the bases along the polymer is the genetic code.
Because DNA is a polymer of nucleotides, its size is easy to count. A strand of 20 nucleotides has 20 sugars, 20 phosphate groups and 20 bases. DNA is not made of protein or sugar alone. You can show its structure by building a 3D model from coloured beads or card shapes, using one colour for each part.