Introduction to Prokaryotes - Online Tutor, Practice Problems & Exam Prep

Prokaryotic & Eukaryotic Cells

In this video, we're going to talk about prokaryotic and eukaryotic cells. And so prokaryotic and eukaryotic are actually the broadest and the most distinct groupings of all life. And the reason for this is because prokaryotic cells actually include 2 different domains of life. It includes both domain bacteria, and it also includes domain archaea as well. And so, both bacteria and archaea are considered prokaryotic.

Now prokaryotic cells specifically do not have an organelle called and so prokaryotic cells do not have a nucleus. Whereas, eukaryotic cells, on the other hand, these are cells that do have a nucleus along with other membrane-bound organelles as well. And so what you'll notice is in prokaryotic and eukaryotic, comparing the two words, they both have this karyo root, and the karyo root is actually referring to the kernel, and it's referring to the kernel of the cell, which is the nucleus. And so karyo is referring to the nucleus, and both, the karyo root is found in both of these words. So both of them are referring to the nucleus.

And really what's different are the roots here pro and eu as we, kind of highlighted up above. Pro and eu is what makes these two words different from each other. So we focus on these roots so we can better understand the meaning of prokaryotic and eukaryotic. And so pro is a root that means before. And so if, you put it together, you get pro or before the, kernel or the nucleus, so before the nucleus.

Before the nucleus is pretty much referring to not having the nucleus because it's before the nucleus. And the eu prefix actually means good. And so, putting this together with the karyote, you get good nucleus, and that means that it does have a good nucleus or just the nucleus. And so hopefully that can help you distinguish between prokaryotic and eukaryotic a little bit better. So down below, we're gonna, take a look at this table here of prokaryotic and eukaryotic cells.

So, notice that the table has these column headers that are the domains of life, the cell type, the nucleus, organelles, cell size, and cellularity. And so, of course, for the domains of life, we know that there are 3 domains of life. There are, domain Bacteria, domain Archaea, and domain Eukarya. Now both bacteria and archaea are, collectively, going to be the same cell type of prokaryotic. And this is because, in terms of the nucleus, both bacteria and archaea, they do not have a nucleus, which means that the nucleus is absent.

Now on the other hand, of course, eukarya are going to be eukaryotic cells, and eukaryotic cells specifically do have a nucleus. So here we can say that the nucleus is present. Now in terms of other membrane-bound organelles, prokaryotic cells, including bacteria and archaea, they do not have membrane-bound organelles, so they will be both, absent here. But, of course, in eukaryotic cells, organelles are going to be present. And moving forward in our course, we'll talk about a lot of these different types of organelles found in eukaryotic cells.

Now once again, in terms of cell size, it's really important to note that prokaryotic cells are significantly smaller than eukaryotic cells, which are significantly larger. And so you can see here that prokaryotic cells, they can range in size, of course, but they're going to be about 1 micrometer here in diameter, whereas eukaryotic cells, which can also range in their sizes, are going to be much larger on average. So here we have a 100 micrometers. So you can see, that eukaryotic cells can be up to 100 times larger than prokaryotic cells in some cases. Now in terms of cellularity, it's important to note that prokaryotic cells, including bacteria and archaea, are actually unicellular, meaning that they're only made up of 1 single cell since uni means 1 or singular.

Whereas, of course, eukaryotic cells, they can either be unicellular or single-celled or they can be multicellular. And so the multicellular organisms that you're aware of are all going to be eukaryotic, and this is, of course, where humans fall. Humans are multicellular. And so this here, concludes our introduction to prokaryotic and eukaryotic cells, and we'll be able to continue to talk more and more about the differences between the two as we move forward in our course. So I'll see you all in our next video.

Which domains of life are classified as prokaryotes?

• A. Bacteria & Eukarya.
• B. Archaea & Fungi.
• C. Bacteria & Archaea.
• D. Bacteria & Protista.

Features of Bacterial Cells

In this video, we're going to talk about some features of bacterial cells, which we know are prokaryotic cells that do not have a nucleus. Now, bacteria are actually the most abundant and the most diverse organisms on Earth, and that's because bacteria are the most ancient organisms on Earth. They're the ones that have been around the longest. Now, bacterial DNA is specifically circular in its shape, and again because bacteria are prokaryotic and they do not have a nucleus, the circular DNA is going to be found in a region that's called the nucleoid. And so the nucleoid is just the name of the specific region where the bacteria's circular DNA can be found.

Now bacteria, like all cells, have structures that are called ribosomes. And ribosomes, we'll get to talk more about these later in our course, but really what you need to know is that ribosomes are found in every single cell and ribosomes are specifically used for building proteins. Now once again, all cells have ribosomes including bacteria, but bacteria, specifically have really, really small ribosomes that we call 70S ribosomes. And the S here is something that we're not going to worry about in our course. It's just a unit, that's referring to the size here of the ribosome, and the 70 here is just the number that goes along with the unit.

Now, bacteria, they have really small ribosomes, and when bacteria divide or multiply into more cells, they divide by a process that's known as binary fission. And so binary fission is a simple process in, with respect to how eukaryotic cells divide, which is a much more complex process. So let's take a look at our image down below so that we can clear some of these things up. So notice that we're showing you the bacterial cell here, and notice that the DNA that we see, right here, this blue circle, represents the circular DNA that nucleoid. And so once again, the nucleoid is just the region where the circular DNA can be found within bacteria.

Now also notice that throughout the cell we have all of these orange dots, and these orange dots represent ribosomes. So notice that we're zooming in here to one of these orange dots, and ribosomes, again, we'll talk more about them later in our course, but basically they are specific for building proteins, and so all cells have ribosomes. But once again, bacteria, they have really really small ribosomes that we call 70S ribosomes. And so this here is representing a 70S ribosome, a small ribosome that bacteria cells have. And so this concludes our introduction to the features of bacterial cells, and we'll be able to compare this to features of eukaryotic cells as we move forward in our course.

So I'll see you all in our next video.

In bacteria, DNA will be found in _______________.

• A. A membrane-enclosed nucleus.
• B. Mitochondria.
• C. The nucleoid.
• D. Ribosomes.

Recap: Prokaryotic vs. Eukaryotic Cells

In this video, we're going to do a recap of prokaryotic versus eukaryotic cells. And so notice down below we have this chart, and the chart is broken up into 3 different sections. We've got the left section over here, which is all about prokaryotic cells, then we have the right section over here in green, which is all about eukaryotic cells, and then in the middle here, we have features of both prokaryotic and eukaryotic cells. And so what you'll notice through the numbering over here and over there is that prokaryotic and eukaryotic cells really have 8 key differences. And so we're going to go through the differences first and then we'll wrap up talking about the similarities.

So the first and major key difference between prokaryotic and eukaryotic cells is that prokaryotic cells, once again, have no nucleus, whereas eukaryotic cells do have a nucleus. Now, also their size is really different; so prokaryotic cells tend to be much smaller, only somewhere between 1 10− micrometers, whereas eukaryotic cells, on the other hand, are much, much larger, and they can be between 10 to 100 micrometers on average, and so that's significantly larger. This means that prokaryotic cells, because they're smaller, are going to be less complex, whereas eukaryotic cells, which are larger, are going to be more complex. Prokaryotic cells are only going to be unicellular, made up of only one single cell. Whereas, eukaryotic cells on the other hand, can either be unicellular or they can be multicellular as well.

All multicellular organisms are going to be eukaryotic. Now, in terms of the DNA, prokaryotic cells have circular DNA in shape, whereas eukaryotic cells, on the other hand, have DNA that is linear in its shape. Prokaryotic cells have absolutely no membrane-bound organelles, whereas eukaryotic cells do have membrane-bound organelles. Now, in terms of the type of cell division, prokaryotic cells divide by a process called binary fission, which is much simpler than the process that eukaryotic cells divide by, and that is going to be mitosis and cytokinesis. And so, we'll talk more about mitosis and cytokinesis later in our course in a different video.

And then last but not least, prokaryotic cells have very small ribosomes that we call 70 S ribosomes, where the 70 here is going to imply the size, indicating that they're smaller. Whereas eukaryotic cells have larger 80 S ribosomes. So, the 80 here is larger than 70, and that's why eukaryotic cells have larger ribosomes. Now those are the 8 key differences between prokaryotic and eukaryotic cells, but once again they do have some similarities that we have here in the middle. And so, both prokaryotic and eukaryotic cells are going to have a cell membrane.

All cells have a cell membrane, and we'll get to talk more about the cell membrane in a different part of our course. Now, also, both prokaryotic and eukaryotic cells contain the major biomolecules that we talked about in some of our previous lesson videos, including carbohydrates, proteins, nucleic acids, and lipids. So both prokaryotic and eukaryotic cells take advantage of these major biomolecules here. And so this here really concludes our recap of prokaryotic and eukaryotic cells, and we'll be able to apply the concepts that we've learned here as we move forward through our course. So I'll see you all in our next video.

Which of the following is/are a primary difference(s) between all prokaryotes and eukaryotic cells?

• A. Prokaryotes have DNA that floats freely in the cytoplasm.
• B. Prokaryotes are significantly smaller than eukaryotic cells.
• C. Prokaryotes do not have ribosomes like eukaryotic cells.
• D. a and b.
• E. a, b, and c

Which of the following is not a common feature shared by all types of cells?

• A. Contains DNA as the genetic material.
• B. Contains a protective cell wall or cell membrane.
• C. Contains a fluid-like portion called the cytoplasm.
• D. Contains a nucleus that stores the genetic material.

You isolate a cell with the following characteristics:(1) no nucleus, (2) a cell wall, and the cell is (3) 2 μm in size. This cell could be a/an:

• A. Bacterium.
• B. Plant cell.
• C. Animal cell.
• D. Bacterial cell or a plant cell.
• E. Plant cell or an animal cell.

Introduction to Archaea

In this video, we're going to begin our introduction to archaea. And so the term archaea is actually a plural term, and the singular form is actually archaeon. And so these are referring to organisms in one of the three domains of life. And again, recall from our previous lesson videos that the three domains of life are bacteria, archaea, and eukarya. And so archaea is one of the major domains of life.

And so like bacteria, archaea also have a prokaryotic cell structure, which makes archaea prokaryotes along with bacteria. And for that reason, many students mistakenly believe that bacteria and archaea are identical because they're both prokaryotes, but that is not the case at all. It turns out that bacteria and archaea are as different from each other as they are from eukaryotes. And so there are still many differences between bacteria and archaea, although they are both categorized as prokaryotes. For example, archaea have unique ribosomal RNA or rRNA sequences that significantly differ from the ribosomal RNA sequences of bacteria and eukarya.

Also, archaea have cell walls that lack the molecule peptidoglycan, whereas recall from our previous lesson videos that bacteria have cell walls made of peptidoglycan. And peptidoglycan is really a molecule that is unique to bacteria, and archaea lack peptidoglycan. And so those are just some of the major differences between bacteria and archaea, but there are also other differences as well. Now archaea are well known for growing in extreme environments, and those that do are known as extremophiles because they can survive in extremely salty environments or extremely hot environments or environments that have extremely high pressures and things of that nature. However, although many archaea do grow in extreme environments and are extremophiles, there are some archaea that can grow in moderate environments as well.

And so they can be found in soils, and they can even be part of the human microbiota as well. And so if we take a look at our image down below, notice again on the left hand side, we're showing you a little snippet of our map of the lesson of the microbial world. And again, we're focusing in on the prokaryotes. We already talked about bacteria, and in this video, we're focusing on the archaea. And so you can once again see that both bacteria and archaea are classified as prokaryotes.

And again, although they're both classified as prokaryotes, meaning that they're going to be unicellular and that they're not going to have a nucleus, they have some similarities but they still have many differences. Bacteria and archaea are not identical. And so over here on the right hand side, we're showing you some examples of archaea. Some are going to be extremophiles in a way where they can grow in extremely salty environments, such as Haloquadratum walsbyi, and this is known as the salt square. And so you can see that it has this square-like arrangement, that it takes up.

And again, it is able to grow in extremely salty environments. Down below, we have some archaea that are capable of growing in extremely hot environments such as Pyrolobus fumarii, which is known as the fire lobe of the chimney. We also have Pyrococcus furiosus, which is known as the furious fireball, and then we have Thermococcus gammatolerans, which is known as the ball of fire. And so these are examples of archaea that can grow in extremely hot environments. And so, again, this here is just our brief introduction to archaea, and we'll be able to talk more about archaea as we move forward in our course.

But for now, this here concludes our introduction and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Many species of Archaea are known to thrive in environments in which most living things would not survive. We call these Archaea… 

• A. Extremophiles.
• B. Thermophiles.
• C. Halophiles.
• D. Acidophiles.
• E. Alkaliphiles.

If you wanted to increase your chances of obtaining a member of Archaea (rather than a member of another domain), which would be the best site to obtain a sample?

• A. Inside a human intestine.
• B. On the surface of human skin.
• C. A 95°C (203°F) hot spring in Yellowstone.
• D. A 22°C (72°F) freshwater spring in Hawaii.
• E. On the surface of a raw hamburger patty.