Examples of key pyrimidines are cytosine, orotic acid, thymine and uracil. Either RNA or DNA can contain cytosine and thymine is usually discovered in DNA. RNA usually has uracil. At times, tRNA has both uracil and thymine.
RNA, DNA and tRNA, which are nucleic acids, play key roles in passing genetic information. For driving most of the body's reactions and as a source of energy, pyrimidines are vital. They are nitrogen-containing bases. When a sugar such as ribose is added to a pyrimidine, a nucleoside is formed. The pyrimidine's name is changed to include an "-idine" suffix. For example, thymine becomes thymidine. Tissues such as the thymus and the spleen make pyrimidines in the human body.