Final answer:
In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C), where purines pair with pyrimidines, and they are held together by hydrogen bonds.
Step-by-step explanation:
Base Pairing in DNA
The nucleotide bases in DNA form specific pairs, where a purine always pairs with a pyrimidine. The correct pairing of nucleotide bases in DNA is adenine (A) with thymine (T), and guanine (G) with cytosine (C). These base pairs are held together by hydrogen bonds, with A and T forming two hydrogen bonds, while C and G form three hydrogen bonds. This complementarity is consistent with Chargaff's rules, which indicate equal amounts of A to T and G to C in DNA, strengthening the structure of the DNA double helix.