Final answer:
Adenine and guanine are purines, while cytosine, thymine, and uracil are pyrimidines. Purines have a double ring structure, while pyrimidines have a single ring. Nucleosides are bases attached to sugar molecules, while nucleotides are composed of a nucleoside plus a phosphate group.
Step-by-step explanation:
The nitrogen-containing bases adenine and guanine are classified as purines, which are nitrogen-containing molecules with a double ring structure. The bases cytosine, thymine (found in DNA only), and uracil (found in RNA only) are classified as pyrimidines, which are nitrogen-containing bases with a single ring structure. Purines and pyrimidines differ in their ring structures, with purines having a double ring and pyrimidines having a single ring.
Adenine and guanine differ from each other in terms of their functional groups attached to their carbon-nitrogen rings. Similarly, the pyrimidines cytosine, thymine, and uracil have different functional groups attached to their carbon-nitrogen ring.
A nucleoside refers to a base (purine or pyrimidine) attached to a sugar molecule, while a nucleotide encompasses the base-sugar molecule combination as well as a phosphate group. So, a nucleotide is composed of a nucleoside plus a phosphate group.