First of all a nucelotide is the monomer that makes up DNA. Millions of monomers are joined together to form the double helix of a DNA molecule. A nucleotide is made of a pentose sugar (in the case of DNA this pentose sugar is called deoxyribose), a organic base (DNA contains four organic bases; adsenosine, thymine, cytosine and guanine) and an inoganic phosphate.