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What are Purines? - Definition & Explanation

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  • 0:00 What Are Purines?
  • 0:35 Structure of Purines
  • 2:00 Purines in Nature and Medicine
  • 3:30 Purines in DNA and RNA
  • 5:10 Storage, Metabolism & Support
  • 6:15 Lesson Summary
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Lesson Transcript
Instructor: Stephen Christensen
In this lesson, you will learn what purines are, how to distinguish them from other molecules, and why purines are so important in biological systems. A quiz at the end of the lesson will test your knowledge.

What Are Purines?

Purines are one of two families of nitrogen-containing molecules called nitrogenous bases. Pyrimidines are the other family of nitrogenous bases. Nitrogenous bases are needed to construct the genetic material in every living organism. Common substances, like caffeine, are purines, and purines are even used to develop many important medications. They are also an essential part of DNA. This places purines, as well as pyrimidines, among the most important of all biological molecules.

Structure of Purines

All purines contain a double-ringed structure that consists of a six-membered ring fused to a five-membered ring; think of a honeycomb cell attached to a pentagon. The purine ring is considered a heterocyclic molecule, meaning it is a closed ring containing at least two different kinds of atoms.

Each of a purine's rings contains two nitrogen atoms, for a total of four within the double-ringed structure. These nitrogen atoms are located in the same positions in all purines. The remaining five positions within the rings are occupied by carbon atoms. The purine ring is encircled by hydrogen atoms, which can be replaced by other atoms or groups of atoms to form different purines.

A ball-and-stick diagram of the purine ring is depicted below. In this representation, carbon atoms are black, nitrogen atoms are blue, and hydrogen atoms are silver. Notice the arrangement of the carbon and nitrogen atoms, which is the same in all purines.

If you're already familiar with pyrimidines - the other family of nitrogenous bases - you may recognize the single, six-membered 'pyrimidine ring' on the left side of purine's double-ringed structure. Not surprisingly, due to their similar structures, these two families of nitrogenous bases share similar chemical properties. While ball-and-stick diagrams are helpful for understanding a molecule's structure, chemists typically use line notation to describe complex molecules.

Purines in Nature and Medicine

Purines are abundant in nature. Some scientists believe purines were among the molecules that existed on primitive Earth prior to the origin of life. The isolation of purines from meteorites that were formed when our solar system was born provides evidence that these molecules could be present in other solar systems, too.

Purines are found in all living organisms, from the simplest viruses to the most complex multi-cellular creatures. Without purines, your chromosomes - and the genetic material in viruses and bacteria - would not exist. Living cells could not produce energy or synthesize most of the molecules they need to function if it weren't for purines. Many important plant-based compounds, such as caffeine and theobromine, are purines, too. We enjoy the stimulant properties of these molecules, but they serve a more practical purpose in their parent plants, where they discourage foraging insects and animals.

Once scientists learned how important purines are to living organisms and how they fit into the scheme of things, it didn't take them long to develop medications based upon the purine ring. Anticancer agents, such as azathioprine and mercaptopurine; asthma medications, like aminophylline; and antiviral drugs, including Zovirax, ribavirin, and ganciclovir, are among the purine-based drugs on the market today.

Purines in DNA and RNA

One of the most important roles purines serve is in the construction of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Paired purines and pyrimidines serve as the building blocks for DNA. Purines are also needed to synthesize RNA, which is then used for producing all of the proteins in your cells; RNA, rather than DNA, is the storage depot for genetic information in many viruses.

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