Here's why:
* Hydrogen bonds are weak electrostatic interactions between a hydrogen atom covalently linked to a highly electronegative atom (like oxygen or nitrogen) and an electron pair in a nearby atom.
* In DNA, the nitrogenous bases (adenine, guanine, cytosine, and thymine) form specific hydrogen bonds with each other. Adenine always pairs with thymine (A-T) through two hydrogen bonds, while guanine always pairs with cytosine (G-C) through three hydrogen bonds.
* These hydrogen bonds are crucial for holding the two strands of the DNA helix together, and for maintaining the double helix structure.
