If a purine is on one side of a DNA molecule, what should be on the other side?

In a DNA molecule, the structure consists of complementary base pairing between nucleotides, which includes two types of nitrogenous bases: purines and pyrimidines. Purines, which are larger and have a double-ring structure, include adenine (A) and guanine (G). Pyrimidines, which are smaller and have a single-ring structure, include cytosine (C) and thymine (T).

When a purine is present on one side of the DNA double helix, it pairs with a pyrimidine on the opposite side. This pairing is essential for the stability of the DNA structure and is governed by the specific complementarity rule: adenine pairs with thymine, and guanine pairs with cytosine. This ensures that the width of the DNA helix remains consistent, vital for its structural integrity.

The other options do not accurately reflect the nature of DNA base pairing. While nucleotide is a broader term that refers to the building blocks of DNA, it can include both purines and pyrimidines and does not specify which type must pair with a purine. RNA is a different nucleic acid altogether, not part of the DNA structure. Thus, the correct pairing for a purine on one side of