1. Sugar-phosphate backbone: This is the structural framework of the DNA molecule. It is formed by alternating sugar (deoxyribose) and phosphate groups.

2. Nitrogenous bases: These are attached to the sugar molecules and form the "rungs" of the DNA ladder. There are four different nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

The sugar-phosphate backbone provides the structural support for the DNA molecule, while the nitrogenous bases hold the genetic information.