The rungs of the DNA “ladder” are made of the nitrogenous bases of the nucleotides, paired together across the two strands.

Quick Scoop

  • Each DNA nucleotide has three parts: a phosphate group, a sugar (deoxyribose), and a nitrogenous base. The base is the information-carrying part.
  • The “sides” or backbone of the ladder are sugar–phosphate chains; these do not make the rungs.
  • The “rungs” are formed where bases on opposite strands hydrogen-bond:
    • Adenine (A) pairs with thymine (T)
    • Cytosine (C) pairs with guanine (G)

So, in short: the rungs of the DNA ladder are the paired nitrogenous bases (A–T and C–G) from each nucleotide, not the sugar or phosphate parts.

Information gathered from public forums or data available on the internet and portrayed here.