nitrogen base

A nitrogenous base is an organic compound that owes its property as a base to the lone pair of electrons of a nitrogen atom. Notable nitrogenous bases include purine bases. Pyrimidine and purine bases include the nucleobases (building blocks of DNA and RNA): adenine, guanine, thymine, cytosine, and uracil. Adenine and thymine/guanine and cytosine are complementary to each other. Adenine pairs only with thymine, and cytosine pairs only with guanine. However, in RNA, adenine pairs with uracil, replacing thymine in the RNA strand. Adenine and guanine are purines, and cytosine and thymine are pyrimidines. They form the rungs of the "twisted ladder" or double helix of DNA.

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