Back To CourseAP Biology: Homework Help Resource
27 chapters | 338 lessons
As a member, you'll also get unlimited access to over 75,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.Try it risk-free
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.
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 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.
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.
Nature can be amazingly conservative. Only 3 pyrimidine bases (thymine, cytosine, and uracil) and 2 purine bases (adenine and guanine) are needed to produce the incredible diversity of species that inhabit the earth. When one purine base is paired with one pyrimidine base, a base pair is formed. When base pairs are joined together to form double-stranded, ladder-like chains of DNA, and when the DNA is coiled into chromosomes, the billions of base pairs that constitute the human genome can be stored within the nucleus of each of your cells. Remember, each base pair in DNA consists of one purine base and one pyrimidine base.
Purines and pyrimidines are used to manufacture RNA, too. Unlike DNA, though, RNA is single-stranded. When base pairs form between purines and pyrimidines in a strand of RNA, they cause the strand to fold upon itself and assume a characteristic shape. Depending on the shape of a given RNA strand, it could have the capacity to 'read' the genetic information stored in your chromosomes, it could carry that message out of the nucleus of the cell, or it could translate the genetic message into proteins.
Storing genetic information isn't the only role purines play in your cells. They also participate in energy transfer and a variety of other critical metabolic processes. Adenosine triphosphate, or ATP, is derived from adenine. The energy stored within the chemical bonds of ATP is used in nearly every metabolic process within your cells. Guanosine triphosphate, or GTP, is similar to ATP in its ability to store and transfer energy, but it is used in fewer metabolic processes than ATP.
Coenzyme A, or CoA, is another important derivative of adenine. Like ATP, coenzyme A is vital for cellular energy production. CoA is also instrumental in synthesizing a wide array of other molecules, such as fatty acids, cholesterol, hemoglobin (the oxygen-carrying pigment in your red blood cells), plant flavonoids and essential oils, and bacterial and fungal antibiotics. In fact, the genes for making CoA have been found in every organism whose genome has been mapped so far.
Let's review. Purines, and the chemically similar pyrimidines, are essential for building DNA and RNA, which makes them indispensable to every living organism. Purines are also necessary for producing, storing, and transferring energy within living cells, and they participate in the synthesis of other metabolically important compounds. Finally, the purine ring has been exploited in a number of pharmaceutical preparations.
Purines have been around for a long time. Some experts believe these molecules arrived on Earth from outer space before life originated here. Whether by fortune or design, the appearance of purines in our world's 'pre-biosphere' was a prerequisite for our very existence.
After you are finished, you should be able to:
To unlock this lesson you must be a Study.com Member.
Create your account
Already a member? Log InBack
Did you know… We have over 160 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.
To learn more, visit our Earning Credit Page
Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.
Back To CourseAP Biology: Homework Help Resource
27 chapters | 338 lessons
Next LessonHigh-Throughput Sequencing of DNA