DNA molecule, ball and stick model. Deoxyribonucleic acid (DNA) consists of two long polymers made up from repeating molecules called nucleotides. A DNA nucleotide is made from one sugar (deoxyribose), a phosphate group and one of four bases: adenine, cytosine, guanine and thymine. The two polymer chains twist around each other to form a double helix: the sugars and phosphate groups form the outer backbone (red, lilac, black and white) while the bases pair together in the middle to form the inner 'rungs' of the helix (blue, black and white). The order in which one type of base follows another in the DNA molecule determines an organism's genetic makeup by forming genes, which are the coding sections of DNA.