Exploring Prokaryotic and Eukaryotic Cells

Understanding cells is an important part of any biology course as cells are the smallest unit of what biologists study. The first important concept to learn about cells is how to classify them into two main groups we see on our planet, which are prokaryotic and eukaryotic. We will discuss these differences throughout the video, but I first want to make one important point before we move on. When looking at pictures or drawings of cells, scale is extremely important. Refer to the 1.1 video for more information about scale bars, magnification. The unfortunate reality is that in many images and drawings of cells the scale bar is not shown. Take this picture here. It looks like something that you would see out of a biology textbook. To the untrained eye it is easy to assume that based on the picture the two cells shown, a general prokaryotic and general eukaryotic cell, are the same size. I mean they look like they are the same size in the picture, right? While the image makes them look similar in size the reality could not be further from the truth. Prokaryotic cells are extremely small compared to eukaryotic cells, so much so that they could easily fit inside of them as they are similar in size to some of the internal eukaryotic structures. More on that later, but for now let's always remember to consider the scale of all images we view, especially the ones without scale bars, so we can understand how all of these cells compare. Let's dive into more detail starting with prokaryotic cells. As mentioned on the last slide, prokaryotic cells are extremely small compared to eukaryotic cells and average a length of about 0.1 to 5.0 micrometers. Aside from being the smaller cells, it is also easy to remember that prokaryotic cells are, in general, more simple. They have less internal components, none of which are wrapped, enclosed, or separated in any meaningful way, and as a product of that have less complicated mechanisms used to control the overall workings of the cell. The DNA in a prokaryotic cell is a single, circular chromosome, and some cells can also have smaller pieces of DNA called plasmids that can hold a few genes and be transferred to other prokaryotic cells. More on that later. All prokaryotic cells have a protective cell wall and a plasma membrane, with some having an additional capsule layer on the outside. You will also find many of these cells with different projections, like a flagella or pili, that can be used for locomotion. Small, simple. Circular DNA with no compartments. Prokaryotic cells are single-celled organisms, meaning they do not come together to make any larger, complex structures bigger than their own individual cells. They do, however, reproduce to create their next generation, just as all living things do. Reproduction for these prokaryotes happens via a process that we call binary fission. This is an easy one to remember because the word binary is in reference to two things and fission means to split something into more than one part. Put those together and you have a great working definition for binary fission, when prokaryotic cells split themselves from one cell into two. To do this, the cell simply makes copies of its internal components, like its circular DNA chromosome, and then splits in half with enough machinery to keep both of the products working. In doing this it creates a clone, or identical copy of the original cell, assuming no mutations occurred in copying the DNA. This process is very fast and efficient, allowing prokaryotic cells like bacteria to grow at exponential rates. Okay, enough about prokaryotes for a minute. Let's move on to talking about eukaryotes. Eukaryotic cells have some stark differences when compared to prokaryotic cells. They are much larger in size, ranging from about 10 to 100 micrometers in length, They have many compartmentalized structures within their cell membrane that are separated by other cell membranes. These structures are called organelles. These organelles work similar to how the organs in your body all work together to achieve the common goal of keeping you alive, but are separated by membranes. These organelles have different functions which we will touch on during the next few slides, but one thing we can mention now is a very important piece for defining eukaryotic cells is that they have a nucleus. The nucleus is a membrane-enclosed structure that holds the DNA of a eukaryotic cell. The DNA does not leave the nucleus if it is present, and the DNA within the nucleus for eukaryotic cells is broken up into different numbers of linear chromosomes, which contrasts the circular structure we looked at for prokaryotic cells. All eukaryotic cells have a cell membrane, like the animal cells that make up you, me, and every other human or animal you know. And some cells, like plant cells, have an additional cell wall structure on top of the cell membrane. Large, complex, linear DNA with compartmentalized organelles. That is how we generally describe eukaryotic cells. On the last slide we discussed that eukaryotic cells contain within them structures called organelles. These organelles are separated from all other internal structures of the cell via their own separate membrane. Each organelle plays a different role in keeping the cell functioning properly. So let's go over a few of these important functions starting with this animal cell. First up we have the nucleus. As mentioned before, the nucleus consists of a double layer membrane called the nuclear envelope. This works to control what substances move in and out of the nucleus and has small pores scattered throughout the envelope to aid that process. Inside the nucleus we find DNA which can be condensed into chromosomes via a structure called chromatin. Additionally, there is a dark spot seen in the nucleus called the nucleolus. which is the location within the nucleus where ribosomes are made. Next up we have the mitochondria. And if you have ever taken a biology class before or have seen any cell biology memes you probably know that this is the powerhouse of the cell. Yes, this structure creates cellular energy called ATP for the cell to use. But there are a few other important points you need to know about the mitochondria. The mitochondria has two membranes surrounding its core structure and the inner layer is highly folded into structures called cristae. Inside the cristae you will find an aqueous solution called the matrix, which is made up of enzymes and other structures to help the mitochondria perform its function. You will learn a lot more about this specific organelle throughout this course. Next up we have the ribosome. Ribosomes are small structures that work to build protein molecules. These structures are made out of two subunits, one large and one small, and are not enclosed by a membrane. making them unique to all other organelles. Next we have the endoplasmic reticulum, which is also commonly referred to as the ER. This organelle is highly folded and adheres to the nucleus. The folds within the membrane are used to create structures called vesicles, which are tiny sacs that pinch off of the folded membrane and are used to transport structures around the cell. The ER has two distinct parts called the smooth and rough ER, also abbreviated SER and RER. The RER has ribosomes embedded into its membrane. As you can recall, ribosomes are used to create proteins, so having them attached to the ER is a great way to create and then also package and ship proteins around the cell. The smooth ER on the other hand does not contain ribosomes. Instead, this section of the ER can create and package other molecules like lipids and also be used to store molecules like calcium. Next up we have the Golgi apparatus. Similar to the ER, this organelle is highly folded. The Golgi receives vesicles from the ER which fuse and grow the membrane. At the ends of the long folds new vesicles are created which get pinched off and sent to different locations. This process of repackaging content allows the cell to sort and modify components before sending or secreting them outside of the cell. This is different from the ER which usually transports materials between organelles inside of the cell. Next up we have the lysosome which is a structure that is unique to the animal cell. These specialized structures carry digestive, or hydrolytic, enzymes that work to break down any food or matter that is taken up by the cell. Internal parts of the cell can also be purposefully destroyed by a lysosome if they are not functioning properly. We'll learn more about this later in the course. To finish up this slide, let's talk about the cell membrane. This structure defines the shape and three-dimensional space of the cell. Its main role is to control the movement of substances that move in and out of the cell. We'll learn more details about the cell membrane in sections 1.3 and 1.4. Let's continue our list of organelles by viewing another type of eukaryotic cell, called a plant cell. Right off the bat, we can see there are a few new structures within the plant cell that we do not find in an animal cell. But many of the structures are the same. Let's highlight a few other important organelles, starting with the chloroplast. The chloroplast is a structure that is unique to the plant cell. This structure has the ability to harness sunlight and create... through a long and complicated process, sugar molecules. This, in essence, is where the process of photosynthesis takes place, which we will discuss in greater detail in topic two. Two other structures that are unique to the eukaryotic plant cell are the central water vacuole and the cell wall. We discussed earlier that eukaryotic animal cells have a cell membrane, and as we can see here, plant cells have a membrane as well. But they also have the addition of this structure called the cell wall. This structure provides support and strength to the cell and is made out of a common plant component called cellulose. This should hopefully be easy to picture as many plants are constantly growing up towards the sun and fighting forces. gravity to do so. This extra strength along with the fact that plant cells do not need to be mobile provides the plant with the force it needs to stand upright. But the cell wall does not provide this force on its own. The other structure that is unique to the plant cell is a large centrally located water vacuole. This vacuole when it is filled provides a type of static pressure that pushes on the cell wall to help the plant tissue stand upright and fight the force of gravity. If plants do not receive enough water to fill this vacuole and provide this needed pressure, you will see the plants start to wilt or bend over to one side. A sign that you need to start watering those indoor plants. Our last two structures you can find in both plant and animal cells, which are centrioles and peroxisomes. Centrioles, which are not pictured here, are structures that help with cell division. They create structures called spindle fibers that can help the chromosomes of the cell divide onto opposite sides of the cell as it splits into two new cells. While both plant and animal cells have these spindle fibers, animal cells also have regions called centrosomes that are attachment sites for these centrioles and spindle fibers. More on that later in the course when we discuss cell division. And finally, we have the peroxisome. This organelle is very similar to the lysosome in the sense that it contains digestive enzymes to break things down. Only this structure can break down a few specific substances like hydrogen peroxide that the lysosome can't. The lysosome is more of a generalist in terms of what it can break down. Biologists have a great understanding of both prokaryotic and eukaryotic cells because of the tools available to study them. In the last video, we discussed microscopes and magnification. And it is this tool, along with many others, that give biologists the ability to perceive and collect data on structures that cannot be seen by the human eye. Microscopes are extremely powerful data collection tools, and there are different microscopes that provide different types of data and detail. The two types of microscopes you need to know are the light microscope and the electron microscope. The light microscope is one that uses a light source to shine through a specimen and is magnified by one or more lenses before it reaches your eye. This can lead to a magnification range in the thousands of times greater than what the normal human eye can perceive. These are common to find in a school classroom and show the natural or stained colors of the observed specimen. The other type of microscope is called an electron microscope, which can be broken down into two categories. Transmission electron microscope and scanning electron microscope. Both of these machines use electrons to generate an image of the specimen that can then be magnified. The difference is that the transmission electron microscope shoots electrons through the specimen to generate an image where the scanning electron microscope has electrons bounce off of the specimen to generate a three-dimensional structure instead of a two-dimensional one. Both of these methods produce a higher range of magnification compared to the light microscope in the range of hundreds of thousands of times greater than what the normal eye can see and produce a picture at a higher resolution meaning the image is more clear to view. The only downside to this method is that you lose any natural color or stain the specimen has. Many of the images you will see on the IB exam will be from an electron microscope, so get used to looking at them.

Refer to the 1.1 video for more information about scale bars, magnification. The unfortunate reality is that in many images and drawings of cells the scale bar is not shown. Take this picture here.

It looks like something that you would see out of a biology textbook. To the untrained eye it is easy to assume that based on the picture the two cells shown, a general prokaryotic and general eukaryotic cell, are the same size. I mean they look like they are the same size in the picture, right?

While the image makes them look similar in size the reality could not be further from the truth. Prokaryotic cells are extremely small compared to eukaryotic cells, so much so that they could easily fit inside of them as they are similar in size to some of the internal eukaryotic structures. More on that later, but for now let's always remember to consider the scale of all images we view, especially the ones without scale bars, so we can understand how all of these cells compare.

Let's dive into more detail starting with prokaryotic cells. As mentioned on the last slide, prokaryotic cells are extremely small compared to eukaryotic cells and average a length of about 0.1 to 5.0 micrometers. Aside from being the smaller cells, it is also easy to remember that prokaryotic cells are, in general, more simple.

They have less internal components, none of which are wrapped, enclosed, or separated in any meaningful way, and as a product of that have less complicated mechanisms used to control the overall workings of the cell. The DNA in a prokaryotic cell is a single, circular chromosome, and some cells can also have smaller pieces of DNA called plasmids that can hold a few genes and be transferred to other prokaryotic cells. More on that later. All prokaryotic cells have a protective cell wall and a plasma membrane, with some having an additional capsule layer on the outside. You will also find many of these cells with different projections, like a flagella or pili, that can be used for locomotion.

Small, simple. Circular DNA with no compartments. Prokaryotic cells are single-celled organisms, meaning they do not come together to make any larger, complex structures bigger than their own individual cells. They do, however, reproduce to create their next generation, just as all living things do.

Reproduction for these prokaryotes happens via a process that we call binary fission. This is an easy one to remember because the word binary is in reference to two things and fission means to split something into more than one part. Put those together and you have a great working definition for binary fission, when prokaryotic cells split themselves from one cell into two.

To do this, the cell simply makes copies of its internal components, like its circular DNA chromosome, and then splits in half with enough machinery to keep both of the products working. In doing this it creates a clone, or identical copy of the original cell, assuming no mutations occurred in copying the DNA. This process is very fast and efficient, allowing prokaryotic cells like bacteria to grow at exponential rates.

Okay, enough about prokaryotes for a minute. Let's move on to talking about eukaryotes. Eukaryotic cells have some stark differences when compared to prokaryotic cells.

They are much larger in size, ranging from about 10 to 100 micrometers in length, They have many compartmentalized structures within their cell membrane that are separated by other cell membranes. These structures are called organelles. These organelles work similar to how the organs in your body all work together to achieve the common goal of keeping you alive, but are separated by membranes. These organelles have different functions which we will touch on during the next few slides, but one thing we can mention now is a very important piece for defining eukaryotic cells is that they have a nucleus.

The nucleus is a membrane-enclosed structure that holds the DNA of a eukaryotic cell. The DNA does not leave the nucleus if it is present, and the DNA within the nucleus for eukaryotic cells is broken up into different numbers of linear chromosomes, which contrasts the circular structure we looked at for prokaryotic cells. All eukaryotic cells have a cell membrane, like the animal cells that make up you, me, and every other human or animal you know.

And some cells, like plant cells, have an additional cell wall structure on top of the cell membrane. Large, complex, linear DNA with compartmentalized organelles. That is how we generally describe eukaryotic cells. On the last slide we discussed that eukaryotic cells contain within them structures called organelles.

These organelles are separated from all other internal structures of the cell via their own separate membrane. Each organelle plays a different role in keeping the cell functioning properly. So let's go over a few of these important functions starting with this animal cell. First up we have the nucleus.

As mentioned before, the nucleus consists of a double layer membrane called the nuclear envelope. This works to control what substances move in and out of the nucleus and has small pores scattered throughout the envelope to aid that process. Inside the nucleus we find DNA which can be condensed into chromosomes via a structure called chromatin. Additionally, there is a dark spot seen in the nucleus called the nucleolus. which is the location within the nucleus where ribosomes are made.

Next up we have the mitochondria. And if you have ever taken a biology class before or have seen any cell biology memes you probably know that this is the powerhouse of the cell. Yes, this structure creates cellular energy called ATP for the cell to use.

But there are a few other important points you need to know about the mitochondria. The mitochondria has two membranes surrounding its core structure and the inner layer is highly folded into structures called cristae. Inside the cristae you will find an aqueous solution called the matrix, which is made up of enzymes and other structures to help the mitochondria perform its function. You will learn a lot more about this specific organelle throughout this course.

Next up we have the ribosome. Ribosomes are small structures that work to build protein molecules. These structures are made out of two subunits, one large and one small, and are not enclosed by a membrane.

making them unique to all other organelles. Next we have the endoplasmic reticulum, which is also commonly referred to as the ER. This organelle is highly folded and adheres to the nucleus.

The folds within the membrane are used to create structures called vesicles, which are tiny sacs that pinch off of the folded membrane and are used to transport structures around the cell. The ER has two distinct parts called the smooth and rough ER, also abbreviated SER and RER. The RER has ribosomes embedded into its membrane.

As you can recall, ribosomes are used to create proteins, so having them attached to the ER is a great way to create and then also package and ship proteins around the cell. The smooth ER on the other hand does not contain ribosomes. Instead, this section of the ER can create and package other molecules like lipids and also be used to store molecules like calcium.

Next up we have the Golgi apparatus. Similar to the ER, this organelle is highly folded. The Golgi receives vesicles from the ER which fuse and grow the membrane. At the ends of the long folds new vesicles are created which get pinched off and sent to different locations.

This process of repackaging content allows the cell to sort and modify components before sending or secreting them outside of the cell. This is different from the ER which usually transports materials between organelles inside of the cell. Next up we have the lysosome which is a structure that is unique to the animal cell.

These specialized structures carry digestive, or hydrolytic, enzymes that work to break down any food or matter that is taken up by the cell. Internal parts of the cell can also be purposefully destroyed by a lysosome if they are not functioning properly. We'll learn more about this later in the course.

To finish up this slide, let's talk about the cell membrane. This structure defines the shape and three-dimensional space of the cell. Its main role is to control the movement of substances that move in and out of the cell.

We'll learn more details about the cell membrane in sections 1.3 and 1.4. Let's continue our list of organelles by viewing another type of eukaryotic cell, called a plant cell. Right off the bat, we can see there are a few new structures within the plant cell that we do not find in an animal cell.

But many of the structures are the same. Let's highlight a few other important organelles, starting with the chloroplast. The chloroplast is a structure that is unique to the plant cell.

This structure has the ability to harness sunlight and create... through a long and complicated process, sugar molecules. This, in essence, is where the process of photosynthesis takes place, which we will discuss in greater detail in topic two. Two other structures that are unique to the eukaryotic plant cell are the central water vacuole and the cell wall. We discussed earlier that eukaryotic animal cells have a cell membrane, and as we can see here, plant cells have a membrane as well.

But they also have the addition of this structure called the cell wall. This structure provides support and strength to the cell and is made out of a common plant component called cellulose. This should hopefully be easy to picture as many plants are constantly growing up towards the sun and fighting forces. gravity to do so.

This extra strength along with the fact that plant cells do not need to be mobile provides the plant with the force it needs to stand upright. But the cell wall does not provide this force on its own. The other structure that is unique to the plant cell is a large centrally located water vacuole.

This vacuole when it is filled provides a type of static pressure that pushes on the cell wall to help the plant tissue stand upright and fight the force of gravity. If plants do not receive enough water to fill this vacuole and provide this needed pressure, you will see the plants start to wilt or bend over to one side. A sign that you need to start watering those indoor plants.

Our last two structures you can find in both plant and animal cells, which are centrioles and peroxisomes. Centrioles, which are not pictured here, are structures that help with cell division. They create structures called spindle fibers that can help the chromosomes of the cell divide onto opposite sides of the cell as it splits into two new cells.

While both plant and animal cells have these spindle fibers, animal cells also have regions called centrosomes that are attachment sites for these centrioles and spindle fibers. More on that later in the course when we discuss cell division. And finally, we have the peroxisome. This organelle is very similar to the lysosome in the sense that it contains digestive enzymes to break things down.

Only this structure can break down a few specific substances like hydrogen peroxide that the lysosome can't. The lysosome is more of a generalist in terms of what it can break down. Biologists have a great understanding of both prokaryotic and eukaryotic cells because of the tools available to study them. In the last video, we discussed microscopes and magnification.

And it is this tool, along with many others, that give biologists the ability to perceive and collect data on structures that cannot be seen by the human eye. Microscopes are extremely powerful data collection tools, and there are different microscopes that provide different types of data and detail. The two types of microscopes you need to know are the light microscope and the electron microscope.

The light microscope is one that uses a light source to shine through a specimen and is magnified by one or more lenses before it reaches your eye. This can lead to a magnification range in the thousands of times greater than what the normal human eye can perceive. These are common to find in a school classroom and show the natural or stained colors of the observed specimen.

The other type of microscope is called an electron microscope, which can be broken down into two categories. Transmission electron microscope and scanning electron microscope. Both of these machines use electrons to generate an image of the specimen that can then be magnified. The difference is that the transmission electron microscope shoots electrons through the specimen to generate an image where the scanning electron microscope has electrons bounce off of the specimen to generate a three-dimensional structure instead of a two-dimensional one.

Both of these methods produce a higher range of magnification compared to the light microscope in the range of hundreds of thousands of times greater than what the normal eye can see and produce a picture at a higher resolution meaning the image is more clear to view. The only downside to this method is that you lose any natural color or stain the specimen has. Many of the images you will see on the IB exam will be from an electron microscope, so get used to looking at them.

Transcript for:Exploring Prokaryotic and Eukaryotic Cells

Transcript for:
Exploring Prokaryotic and Eukaryotic Cells