Microbiology, part 14: Eukaryotes - Plasma Membrane, Cell Wall, ECM, Flagella, & Cilia

Hi. I'm Cathy with Level Up RN. In this video, I'm going to continue my coverage of eukaryotic cells. In my last video, we talked about structures found inside the plasma membrane. In this video, we're going to talk about the plasma membrane as well as structures found outside the plasma membrane, including a cell wall, an extracellular matrix, flagella, and cilia. At the end of the video, I'm going to give you guys a quiz to test your understanding of some of the key points I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcards so you can follow along with me.

First, let's talk about the plasma membrane, which is a phospholipid bilayer that surrounds the cell's cytoplasm. It exhibits selective permeability, which means it only allows certain materials to enter and exit the cell. Small nonpolar molecules, such as oxygen and carbon dioxide, can diffuse freely across the membrane. However, the membrane is impermeable to larger polar molecules. The plasma membrane has the consistency of oil, so it is not a solid structure. It is often described in terms of the fluid mosaic model, which means that components of the membrane are able to move freely within the membrane.

Proteins are embedded in the plasma membrane and serve a number of functions. Transmembrane proteins span the entire plasma membrane. An example of a transmembrane protein is a protein channel, which allows the transport of specific molecules across the membrane. Peripheral proteins are proteins that do not span the entire plasma membrane, and they serve a number of functions. They provide structure for the cell, and some act as enzymes or receptors. You will also find glycoproteins and glycolipids extending out from the plasma membrane into the extracellular environment, so outside the cell. Glycoproteins are proteins attached to carbohydrates, and glycolipids are lipids attached to carbohydrates. The key function of these structures is cell-to-cell communication.

One important difference between eukaryotic cells and prokaryotic cells is that the plasma membrane in eukaryotic cells contain sterols such as cholesterol. Cholesterol affects the fluidity, rigidity, and permeability of the membrane. So at low temperatures, cholesterol will prevent the membrane from being too rigid and freezing. And at high temperatures, cholesterol helps the membrane from becoming too fluid and too permeable.

Working our way outside the plasma membrane now. Some eukaryotic cells will have a cell wall, which protects the cell and provides structural support. Animal and protozoan cells do not have a cell wall. However, fungi, algae, and plants do have a cell wall. This cell wall may be composed of a variety of materials. In plants, it is made up of cellulose. In fungi, it is made up of chitin. And in some algae, it may be made up of silica. Cells that don't have a cell wall, such as animal cells, produce an extracellular matrix. This is a network of proteins and carbohydrates that helps to protect the cell. The extracellular matrix also allows the cell to attach to other cells, and it transmits signals from outside the cell to the inside.

Next, let's talk about flagella, which are structures that help the cell to move. Eukaryotic flagella are composed of a complex of microtubules. These microtubules are long hollow tubes made up of the protein tubulin arranged in a nine plus two array, which means we have nine pairs of microtubules surrounding a central pair of microtubules. Unlike prokaryotic flagella that move in a propeller-like fashion, eukaryotic flagella move in a whip-like fashion. Another key difference between flagella in eukaryotic cells and prokaryotic cells is that eukaryotic flagella are surrounded by the plasma membrane, whereas prokaryotic flagella are not.

Lastly, let's talk about cilia, which are structures unique to eukaryotic cells. Cilia are structurally similar to flagella, but they are shorter, and they cover the whole surface of the cell. Cilia can be used for locomotion or to move particles past or into cells. For example, ciliated cells in the respiratory tract move debris towards the pharynx where it can be coughed or sneezed out or swallowed.

All right. It's quiz time, and I have five questions for you. Question number one, eukaryotic cell walls contain cholesterol. True or false? The answer is, true. Question number two, which of the following cells have a cell wall: animal cells, algae cells, and/or plant cells? The answer is, algae and plant cells. Animal cells do not have a cell wall. Number three, eukaryotic flagella move in a propeller-like fashion. True or false? The answer is, false. They move in a whip-like fashion, whereas prokaryotic flagella do move in a propeller-like fashion. Number four, what structures found on the surface of eukaryotic cells are short, cover the entire cell, and help move particles past or into cells? The answer is, cilia. Number five, what do you call the network of proteins and carbohydrates that surround eukaryotic cells that do not have a cell wall? The answer is, the extracellular matrix.

All right. That's it for this video. I hope it was helpful. Take care, and good luck with studying.

[BLOOPERS]

In fungi, it's made of chitin, and in some algae, it may-- oh, boy. Which carry out various functions.