Here's how it works:

* Sugar-phosphate backbone: This is the "side" of the DNA ladder, made up of alternating sugar (deoxyribose) and phosphate groups.

* Nucleotide rungs: Each rung is made of a pair of nitrogenous bases (adenine with thymine, or cytosine with guanine).

* Attachment: The nitrogenous bases within each nucleotide are attached to the sugar molecules in the backbone. The sugar molecules are connected to the phosphate groups, forming the continuous sugar-phosphate backbone.

So, the bases are effectively "hanging off" the sugar-phosphate backbone, forming the rungs of the DNA ladder.