Deoxyribonucleic acid (DNA) is the genetic material for all cellular organisms, with the “nucleic” part coming from the location of DNA in the nuclei of eukaryotic cells. The discovery of DNA is considered the most important molecular discovery of the twentieth century. It is actually a polymer (long strand) of nucleotides. A nucleotide has three component parts: a phosphate group, a five-carbon sugar (deoxyribose), and a nitrogen base. If you visualize DNA as a ladder, the sides of the ladder are made of the phosphate and deoxyribose molecules, and the rungs are made of two different nitrogen bases. The nitrogen bases are the crucial part of the molecule with regard to genes. Specific sequences of nitrogen bases make up a gene.