Question

what is difference between purines and pyrimidines?

Answer 1

Purines consist of two fused rings, whereas a pyrimidine has only one. The pyrimidine ring is a hexagon with six atoms, two of which are nitrogens; the nitrogens are situated at positions 1 and 3 (counting counterclockwise from the atom at the bottom of the ring). A purine has a pyrimidine ring that is fused with an imidazole ring, a smaller, pentagon-shaped ring that has only five atoms with a nitrogen at positions 1 and 3.