What Is an Alkaloid? - Definition & Examples

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  • 0:00 What Are Alkaloids?
  • 1:17 Examples in Medicine
  • 3:39 Examples of Psychotropic Drugs
  • 4:50 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll go over what alkaloids are and where they are found in nature. Then we'll give some important examples in medicine and psychotropic drugs.

What Are Alkaloids?

When you think of nitrogen, you might be picturing a race car expelling blue flames from a nitrous oxide tank. Or you might be thinking of nitrogen in fertilizers, leisurely applied to farms with a tractor.

Although these are great uses for nitrogen, important molecules in our body also use nitrogen. Nitrogen is actually just an atom, and atoms bound together make up molecules. Naturally occurring molecules that are composed of nitrogen and carbon are called alkaloids. Alkaloids usually have a ring structure, which includes at least one nitrogen atom.

Alkaloids are basic, meaning they can absorb acid, or hydrogen ions. Some bases you might be familiar with include milk, calcium carbonate in antacids, or ammonia in cleaning products. Alkaloids are single molecules, so they are small, and they can absorb hydrogen ions, making them a base.

Alkaloids are made by all living things, but many alkaloids are isolated from plants. Most plants only produce a few types of alkaloids and the function of them in plants is not clear. Some scientists think they may be involved in seed production. Regardless of their role in plants, many alkaloids have uses in medicine for humans.

Examples in Medicine

Alkaloids derived from plants have a long-standing place in medicine. Pain killers derived from the poppy plant, like morphine, have been around since 1805. The antimalarial drug quinine has been used by tribes in the Amazon for over 400 years. Let's look more in detail about some of these important alkaloids.

Morphine is a powerful painkiller, usually used when someone needs surgery or has a severe injury. Morphine attaches to sites on our nerve cells and prevents them from receiving messages about pain from the body. The result is a euphoric state with no pain. Although perfect for surgery, this alkaloid is extremely addicting and can become a drug of abuse.

Derivatives of morphine include oxycodone, which is used as a pain medication but is also extremely addictive and heroin. Heroin was designed as a drug to replace morphine in hospitals, but now has no medical use. It is only used illegally for its euphoric effects and users can quickly become dependent on this alkaloid.

You've probably heard of malaria, a parasite transmitted by mosquitos. Malaria infects blood cells, releasing toxins into the blood that can cause flu-like symptoms, which can turn fatal in some patients. When a person has malaria, doctors use an alkaloid called quinine to treat them. Most patients take quinine for three to seven days and will feel better within a day or two after the treatment has started. Although essential to curing patients of malaria, this alkaloid has some side effects, like low blood sugar, nausea, and some psychological effects, such as nervousness or confusion.

Atropine is an alkaloid isolated from Atropa belladonna, or deadly nightshade. The purple flowers and berries of the belladona are quite beautiful but are lethal if consumed by humans. However, alkaloids carefully derived from this plant can be used in medicine. Atropine is one example which prevents messages from being sent from the brain to muscle. The brain communicates with the muscle using a chemical called acetylcholine, so atropine is called an anticholinergic medication.

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