DNA is made up of six smaller molecules; a five carbon sugar called deoxyribose, a phosphate molecule, and four different nitrogenous bases (adenine, thymine, cytosine and guanine). The model is known as a double helix because two long strands twist around each other like a "twisted ladder." The rails of the ladder are made of alternating sugar and phosphate molecules. The steps of the ladder are made of two bases joined together.