Best Answer: Nitrogenous bases: A=Adenine T=Thymine G=Guanine C=Cytosine Each base attached to a pentose/five carbon sugar (deoxyribose), and a phosphate group. The phosphate and sugar molecules bind to each other with covalent bond, while the complementary bases bind with hydrogen bond.hey are attached to a five carbon sugar through covalent bonds, and they also form the rungs of the ladder in the double helix through hydrogen bonds. These hydrogen bonds are between two nitrogenous bases.