The "rungs" of the DNA molecule are made up of pairs of nitrogenous bases. These bases pair specifically: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G) through hydrogen bonds. These base pairs form the steps or rungs of the DNA double helix ladder structure

. Each nucleotide in DNA consists of a nitrogenous base attached to a sugar (deoxyribose) and a phosphate group. The sugar-phosphate groups form the backbone (the sides of the ladder), while the nitrogenous bases extend inward and pair to form the rungs

. In summary:

• The rungs = paired nitrogenous bases (A-T and C-G)
• The bases are held together by hydrogen bonds
• The sides/backbone = alternating sugar (deoxyribose) and phosphate groups

This complementary base pairing is essential for the DNA's structure and function in storing genetic information