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Prokaryotes & Eukaryotes: Definition & Examples

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  • 0:00 Prokaryote or Eukaryote?
  • 0:25 Prokaryotes
  • 1:10 Examples of Prokaryotes
  • 3:45 Eukaryotes
  • 4:25 Examples of Eukaryotes
  • 5:35 Lesson Summary
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Lesson Transcript
Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

Every living organism can be categorized as either a prokaryote or a eukaryote. There are many different examples of both types of organisms. Learn about prokaryotes and eukaryotes, and test your knowledge by answering the quiz questions.

Prokaryote or Eukaryote?

Have you or anyone you know ever had strep throat before? If so, then you, a eukaryote, have become acquainted with a prokaryote. Now, you are probably asking several questions at this point. What in the world is a eukaryote? What is a prokaryote? How am I a eukaryote? Which prokaryote did I get to know? Well, let's get you the answers to your questions.

Prokaryotes

Prokaryotes are 1-celled organisms that do not have a nucleus or any other membrane-bound organelles inside them. The name prokaryote itself actually lets you know that there isn't a nucleus, since pro means before and karyo refers to nucleus.

Prokaryotes are filled with cytoplasm and contain very few and basic internal structures. The genetic information is carried on circular pieces of DNA. There may be only one piece of DNA or many pieces of DNA. The only organelles, or internal structures that exist in prokaryotes are ribosomes, which make proteins needed by the organism. Prokaryotes include Archaea, bacteria and cyanobacteria. That answers the question about what a prokaryote is.

Examples of Prokaryotes

So, now let's address the question about which prokaryote you became familiar with during that case of strep throat. Strep throat is caused by a Group A strep bacterium called streptococcus pyogenes. 'S. pyogenes are gram-positive and do not move on their own. This bacterium causes strep throat and can also cause impetigo, scarlet fever and cellulitis - and a few other diseases in our bodies.

While this may not have been such a happy meeting with this prokaryote, these bacteria are able to live in our bodies and not cause any disease at all. As a matter of fact, there are many bacteria that are helpful in our bodies. Let's discuss one now.

It would be very difficult to break down the foods we eat without the help of bacteria. One bacterium that helps to break down food is lactobacillus acidophilus. L. acidophilus reside naturally in our gastrointestinal tract. These bacteria like to grow in very acidic areas and convert the sugar lactose into lactic acid. This action is what allows us to enjoy dairy products, such as that melted cheese on a slice of pizza. Yum!

Let's also talk about the prokaryote cyanobacteria mentioned earlier.

Cyanobacteria

Cyanobacteria are unique in many ways. These are considered to be the oldest living organisms on the Earth and are the most abundant of the prokaryotes. They are able to make their own food through photosynthesis, and through that process, they have released a lot of the oxygen we breathe. Cyanobacteria live in water and are often found living together in clumps known as colonies. Cyanobacteria are often used in fertilizer to help with the growth of different crops. So, while there are some prokaryotes that can be harmful, there are many that are very useful and necessary for us to survive.

Finally, when talking about prokaryotes, we can't forget about the domain archaea. Although they were once classified as bacteria, these single-celled microorganisms make up their own domain. While many species of archaea are similar in size and shape to bacteria, they possess a different genetic structure and biochemistry. They were first thought of as extremophiles because they were found in harsh environments, such as volcanic vents and the Dead Sea. We know today, though, that archaea can inhabit a wide range of environments and are particularly abundant in the oceans.

Eukaryotes

Eukaryotes developed many years after prokaryotes and are substantially more complex. Their name also tells you about the nucleus, since eu- means 'true,' and we know already that karyo- means 'nucleus.'

These organisms are either single-celled or multicellular. They contain a membrane-bound nucleus as well as membrane-bound organelles such as mitochondria, endoplasmic reticulum and the Golgi complex. The nucleus contains DNA, which is organized into linear chromosomes. Eukaryotes depend on the different organelles in order to carry out the various functions of the cell in order to sustain life.

Example of Eukaryotes

We already established early on that you are a eukaryote. All humans, homo sapiens, are eukaryotes, and you likely know quite a bit about yourself and other people, so let's look at some other examples of eukaryotes. All plants, animals and fungi fall under the category of eukaryote. Any living organism that you can see with your naked eye is a eukaryote.

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