Which options apply to Purines and Pyrimidines? Purines: 1) contain one heterocyclic ring 2) contain two heterocylic rings 3) contain only two ring nitrogens 4) contain only three ring nitrogens 5) contain four ring nitrogens Pyrimidines: 1) contain one heterocyclic ring 2) contain two heterocylic rings 3) contain only two ring nitrogens 4) contain only three ring nitrogens 5) contain four ring nitrogens Purine vs Pyrimidine 1) guanine 2) cytosine 3) thymine