The DNA has a double helical structure, which is made up of the molecules known as the nucleotides. Each of these nucleotide molecule is composed of the deoyribose sugar, phosphate group, and a nitrogenous base. The nitrogenous bases are of two types, namely the purines, and pyrimidines. The deoxyribose sugar and the nitrogenous base bonded covalently would be known as nucleoside-nitrogenous base + sugar.