The structure in DNA and RNA that is similar is the backbone. The backbone of both DNA and RNA is made up of a series of alternating sugar and phosphate molecules. In DNA, the sugar is deoxyribose, while in RNA, the sugar is ribose. The phosphate molecules are the same in both DNA and RNA. The backbone of DNA and RNA forms a double helix, which is a twisted ladder-like structure. The sugar and phosphate molecules form the sides of the ladder, while the nitrogenous bases form the rungs.