Final answer:
Purines and pyrimidines are nitrogenous bases found in DNA and RNA. Purines have a double-ring structure, while pyrimidines have a single-ring structure. The numbering convention for the atoms in these structures designates primed numbers for the atoms of the pentose ring and unprimed numbers for the atoms of the purine or pyrimidine ring.
Step-by-step explanation:
Purines and pyrimidines are nitrogenous bases found in DNA and RNA. Purines have a double-ring structure with a six-membered ring fused to a five-membered ring, while pyrimidines have a single six-membered ring structure. The numbering convention for the atoms in these structures designates primed numbers for the atoms of the pentose ring and unprimed numbers for the atoms of the purine or pyrimidine ring.