The sides of the ladder are made of alternating sugar and phosphate molecules. The sugar is deoxyribose. The rungs of the ladder are pairs of 4 types of nitrogen bases. Two of the bases are purines- adenine and guanine.
The shape of DNA is a double helix, which is like a twisted ladder. The sides of the ladder are made of alternating sugar and phosphate molecules. Deoxyribose, which is a pentose, and a phosphate group are the two molecules that together form the two sides of the DNA. The rungs of the ladder are pairs of 4 types of nitrogen bases.
