What makes up the steps of the DNA spiral staircase

The DNA molecule consists of two strands that wind around one another to form a shape known as a double helix. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases--adenine (A), cytosine (C), guanine (G), and thymine (T). #DNAChemicalCompound #Genetics #RNA #Uracil #thymine #cytosine #Guanine