The base pairing is regular and precise. The combination of a deoxyribose and a base constitutes a deoxynucleoside . The combination of a phosphate, a deoxyribose and a base constitutes a deoxynucleotide. DNA is a double helix. It is confirmed by diffraction data.
Models using beads are useful to handle the concept.
E. coli has a single circular DNA molecule of 4,600,000 base pairs. The total length is 1.4 mm. In man, the DNA molecule in a diploid cell, if fully extended, would have a total length of 1.7 metres. Compare a deoxyribose with a ribose . The third one gives the phosphoribo-backbone an acidic property.