Final answer:
Adenine and guanine are classified as purines, which have a double ring structure. They are represented by the symbols A and G and are found in DNA and RNA.
Step-by-step explanation:
Adenine and guanine are both classified as purines. Purines are nitrogen-containing molecules with a double ring structure that accommodates several nitrogen atoms.
On the other hand, pyrimidines are nitrogen-containing bases with a single ring structure. Cytosine, thymine, and uracil are examples of pyrimidines. In molecular biology shorthand, these bases are represented by the symbols A, G, C, T, and U for DNA and RNA.