The phosphate is negatively charged at anything near physiological pH. This increases water solubility, makes transport across membranes difficult, and imparts a high binding affinity for positively charged ions. B. Primary structure 1. The backbone of the polymer consists of alternating sugars and phosphates. The bases are appended to the sugars and stick out from the backbone. Sometimes the phosphates are indicated explicitly in diagrams, but often the entire backbone is implicit and just the order of bases is given.
Genetic information is encoded in the sequence of the bases along a DNA molecule.
Because of the asymmetry of the sugar, a polynucleotide chain has inherent polarity. We orient the strands using the deoxyribose to distinguish the parts of the chain attached to the 5' and 3' positions of the sugar. This means that the double helix maintains a regular, repeating structure in its backbone, regardless of the base sequence. The bases are aligned perpendicular to the helix axis. The two grooves in the double helix are unequal in size.