DNA consists of deoxyribose sugars connected by phosphodiester bonds. The bases that are covalently linked to each deoxyribose sugar are the key to the genetic code within the DNA molecule. The four nitrogenous bases are two purines and two pyrimidines. What are the correct classifications for the four bases (adenine, cytosine, guanine, thymine)? 1. Pyrimidines = adenine and guanine; purines = cytosine and thymine 2. Pyrimidines = cytosine and thymine; purines = adenine and guanine 3. Pyrimidines = cytosine and guanine; purines = adenine and thymine 4. Pyrimidines = cytosine and adenine ; purines = thymine and guanine