Here's why:

* DNA and RNA Bases: DNA and RNA are made up of nucleotide building blocks. Each nucleotide contains a sugar, a phosphate group, and a nitrogenous base.

* Nitrogenous Bases: There are five main nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). All of these bases contain nitrogen atoms within their molecular structure.

* Importance of Nitrogen: Nitrogen is a key element in forming the specific chemical bonds and interactions that allow the bases to pair up (A with T/U, and C with G) within DNA and RNA. These base pairings are fundamental to the structure and function of these genetic molecules.