The nucleic acid bases exhibit distinct differences in their chemical structures and pairing properties.

Nucleic acid bases serve as the fundamental components of DNA and RNA. In DNA, there are four primary types of bases: adenine ($A$), guanine ($G$), cytosine ($C$), and thymine ($T$). In contrast, RNA contains uracil ($U$) instead of thymine. The bases are categorized based on their structures, with adenine and guanine classified as purines, which possess a double-ring structure, while cytosine, thymine, and uracil are categorized as pyrimidines, characterized by a single-ring structure.

The bases also vary in their pairing properties. In DNA, adenine pairs with thymine ($A$-$T$), and in RNA, adenine pairs with uracil ($A$-$U$). Guanine pairs with cytosine ($G$-$C$) in both DNA and RNA. The pairing occurs through hydrogen bonding, where the $A$-$T$ base pair is held together by two hydrogen bonds, while the $G$-$C$ base pair is stabilized by three hydrogen bonds. This difference in the number of hydrogen bonds contributes significantly to the overall stability of the DNA double helix.

Moreover, the bases play varying roles in the storage and expression of genetic information. Alterations in the sequence of these bases can lead to changes in the amino acid sequences of proteins, ultimately affecting their functionality. Additionally, certain bases are more susceptible to mutations; for instance, cytosine ($C$) is more prone to spontaneous mutations compared to adenine ($A$), guanine ($G$), or thymine ($T$).

In summary, nucleic acid bases differ in their chemical structures, pairing properties, and roles in genetic information processing. Understanding these differences is crucial for comprehending the structure and function of DNA and RNA.