What are the two types of nucleotide bases which make up DNA, and which bases bond with one another? What is the difference with these bases in RNA?

The two types of nucleic bases are purines and pyrimidines. The purines are adenine and guanine, and the pyrimidines are cytosine and thymine. Purines always bond with pyrimidines and in DNA, adenine and thymine always bond to form the backbone, and cytosine and guanine bond. In RNA, the pyrimidine thymine is replaced by the pyrimidine uracil.