The most common nitrogenous bases are adenine, cytosine, guanine, thymine, and uracil. DNA contains four different nitrogenous bases&colon; adenine, guanine, cytosine and thymine. The nucleobases are divided into purines (guanine and adenine) and pyrimidines (cytosine, thymine and uracil). Pyrimidines include thymine, cytosine, and uracil. In RNA, uracil base-pairs with adenine and replaces thymine during DNA transcription. Py denotes pyrimidine which can be either cytosine or thymine. It consists of 4 nucleotides guanine, thymine, cytosine, and adenine. Pyrimidine is a component of the nucleobases cytosine, uracil, and thymine. The shape of adenine is complementary to either thymine in DNA or uracil in RNA. Uracil is a demethylated form of thymine. The three others are guanine, cytosine and thymine. These are examples of modified cytosine, thymine or uridine. RNA also contains the base uracil in place of thymine. In DNA, these bases form hydrogen bonds with their complementary pyrimidines, thymine and cytosine, respectively. Inosine occurs in tRNAs, and will pair with adenine, cytosine, or thymine.