Final answer:
Hydrogen bonds join adenine to thymine and guanine to cytosine in the structure of DNA, maintaining its uniform double helix shape.
Step-by-step explanation:
Specifically, adenine (A) pairs with thymine (T) with two hydrogen bonds, and guanine (G) pairs with cytosine (C) with three hydrogen bonds. This complementary base pairing is what maintains the uniform shape of the DNA double helix, where the distance between the two strands is kept constant thanks to the binding of a one-ring molecule (thymine or cytosine) with a two-ring molecule (adenine or guanine), forming the steps of the spiral staircase.