Base pairing in DNA refers to the specific bonding between the nitrogenous bases in the DNA double helix. The four nitrogenous bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T). These bases form the rungs of the DNA ladder and are held together by hydrogen bonds.
A always pairs with T, and C always pairs with G. This specific base pairing is what allows for the accurate replication and transmission of genetic information from one generation to the next.
Because of base pairing, the percentage of adenine molecules in DNA is about equal to the percentage of guanine molecules. This is because A always pairs with T, and G always pairs with C, so the proportion of A and T must be equal, as must the proportion of G and C.
Similarly, the percentage of pyrimidines (C and T) in DNA is about equal to the percentage of purines (A and G) in DNA. This balance of purines and pyrimidines helps to maintain the stability of the DNA double helix.
Therefore, the correct answer is a: Adenine molecules in DNA are about equal to the percentage of guanine molecules.