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Nitrogenous bases

A nitrogenous base is a molecule that contains nitrogen and that has the chemical properties of a base (rather than an acid). They are a component of nucleic acids such as DNA.

There are five different nitrogenous bases (abbreviated by their first letter) that occur in nucleic acids. They fall into two groups:

  • Pyrimidines: thymine (T), cytosine (C) and uracil (U) contain only a single hexagonal ring of carbon and nitrogen atoms.
  • Purines: adenine (A) and guanine (G) contain two rings of carbon and nitrogen atoms.

Thymine and uracil are similar in structure but thymine only bonds with deoxyribose and uracil only bonds with ribose. Uracil would make DNA less stable so thymine is used instead.

As a result, DNA contains thymine, adenine, guanine and cytosine. RNA contains uracil, adenine, guanine and cytosine.

Pyrimidines have one ring of carbon and nitrogen atoms while purines contain two.
Pyrimidines have one ring of carbon and nitrogen atoms while purines contain two.