Pyrimidines: Definition & Examples Video

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  • 0:01 What Are Pyrimidines?
  • 0:33 Structure
  • 1:21 Examples
  • 2:07 Function
  • 4:06 History
  • 4:39 Lesson Summary
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Lesson Transcript
Instructor: Stephen Christensen
In this lesson, you'll learn about the important functions of pyrimidines and discover why these compounds are essential to life. You'll also learn how to identify molecules containing pyrimidines.

What Are Pyrimidines?

Pyrimidines are one of two biologically important families of nitrogen-containing molecules called nitrogenous bases. Purines are the other family of nitrogenous bases. Pyrimidines can be identified by their structure: six atoms in the shape of a ring. This ring is known as a pyrimidine ring. The pyrimidine ring is a heterocyclic compound, which means it contains atoms from at least two different elements. A homocyclic compound, on the other hand, contains atoms from only one element.


As shown in the ball-and-stick diagram, the pyrimidine ring consists of two nitrogen atoms and four carbon atoms. The nitrogen and carbon atoms in a pyrimidine ring are always arranged in the same way, with the two nitrogen atoms separated by a single carbon atom and the other three available positions occupied by carbon atoms. Four hydrogen atoms are attached to the outside of the pyrimidine ring to stabilize it electrically. In this diagram, carbon atoms are gray, nitrogen atoms are blue, and hydrogen atoms are white. Different pyrimidines are formed by placing different atoms at various positions around the pyrimidine ring.

Pyrimidine Ring

Although ball-and-stick diagrams are easier to understand, chemists typically use line notation to depict complex molecules like pyrimidines. Line notation for the pyrimidine ring would look like this:

Pyrimidine Ring Line Notation


The pyrimidine ring provides the backbone for a number of natural and synthetic molecules. For example, thiamine, or vitamin B1, is based on a pyrimidine ring. Many naturally occurring antibiotics and an assortment of alkaloids from plants and marine organisms are also derived from pyrimidines. Pyrimidine-based alkaloids fulfill a variety of functions in living organisms, including protection from predators, parasites and infections.

Can you identify the pyrimidine ring in this line notation diagram of thiamine? (It is the six-sided ring on the left side of the diagram.)
Thiamine Line Notation

Taking their cue from nature, scientists have developed a wide array of pharmacologic agents that are based on the pyrimidine ring. Fluorouracil, an anti-cancer drug; zidovudine, an anti-HIV medication; Pentothal, an anesthetic, and trimethoprim, an antibiotic, are a few examples.


Arguably the most important function of pyrimidines is in the construction of deoxyribonucleic acid, or DNA and ribonucleic acid, RNA. This genetic material, which guides your cells' day-to-day functions and assures the reproduction of every living thing on earth, would not exist without pyrimidines. When paired with purines, pyrimidines serve as the building blocks for DNA, which is the basis for your genes and chromosomes. When incorporated into RNA, pyrimidines participate in the mechanism that produces all of the proteins in your cells.

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