If you have a purine on one side of the DNA strand, what will be present on the opposite side?

In DNA, the structure is characterized by the pairing of nucleobases that are classified into two categories: purines and pyrimidines. Purines, which include adenine (A) and guanine (G), are always paired with pyrimidines, which include cytosine (C) and thymine (T) in DNA. This specific pairing is due to the hydrogen bonding patterns that allow for stable base pairing, with purines forming two hydrogen bonds with pyrimidines (A with T) and three hydrogen bonds in the case of G with C.

This complementary base pairing is essential for the double-helix structure of DNA, maintaining uniform width and allowing for accurate replication and transcription processes. When a purine is present on one side of the DNA strand, the opposite side will necessarily have a pyrimidine to maintain this specific pairing.

Other given choices, such as protein, amino acid, or carbohydrate, are not relevant in this context as they do not participate directly in the base pairing of DNA. Hence, the presence of a purine on one side of the DNA strand guarantees the presence of a pyrimidine on the opposite side.