The two strands of DNA molecules, also known as the double helix, are held together by hydrogen bonds. These hydrogen bonds form between the nitrogenous bases on the opposite strands. Specifically, the nitrogenous bases adenine (A) pairs with thymine (T), while guanine (G) pairs with cytosine (C). This pattern is often referred to as the "base pairing rule" or "complementary base pairing."

1. Adenine (A) with Thymine (T): Adenine forms two hydrogen bonds with thymine, contributing to the stability of the DNA structure.

2. Guanine (G) with Cytosine (C): Guanine forms three hydrogen bonds with cytosine, establishing a stronger bond compared to the A-T pair.

The hydrogen bonds between the base pairs hold the DNA strands together, creating a specific structure that is crucial for accurate DNA replication, gene expression, and the overall integrity of genetic information.