Prokaryotic Flagellar Structure - Online Tutor, Practice Problems & Exam Prep

Prokaryotic flagella consist of three main components: the filament, hook, and basal body. The filament, made of flagellin, is the primary structure. The hook connects the filament to the basal body, which anchors the flagellum to the cell. In gram-positive bacteria, the basal body has two protein rings (MS and C rings), while gram-negative bacteria have four rings (adding L and P rings) due to an outer membrane. Understanding these structures is crucial for grasping bacterial motility and the differences between gram-positive and gram-negative bacteria.

Prokaryotic Flagellar Structure

In this video, we're going to begin our lesson on prokaryotic flagellar structure. A prokaryotic flagellum consists of 3 parts that we have numbered down below, 1, 2, and 3. These numbers in the text correspond with the numbers that we have in our image. It's important to keep this correspondence in mind as we go through the video.

The first structural component of a prokaryotic flagellum is the filament, which is the primary component of the flagellum. It is made of the globular protein called flagellin. If you take a look at the image below for number 1, you'll notice that the filament is represented by the blue structure. It is the main component of the flagella made of globular protein flagellin.

The second structural component is the hook, which is a flexible curved protein that connects the filament to the basal body, the third component. If we look at the image below, the hook is shown in green. It mainly serves to connect the filament to the basal body.

Moving to the third part, the basal body consists of a rod along with protein rings, as can be seen in the images. The basal body, embedded in the cell envelope's membranes by a series of protein rings, directly attaches to the hook. This setup includes both the rod and the protein rings as indicated by the brackets. This assembly is typical for the structure of a prokaryotic flagellum.

As we move forward, we will discuss the differences between gram-positive and gram-negative prokaryotic flagella. I'll see you all in our next video.

Which of the following is NOT a component of bacterial flagella?

• A. Flagellin
• B. Basal body
• C. Tubulin
• D. Filament
• E. Hook

Structure of Gram-Positive Basal Body

In this video, we're going to talk about the structure of the flagella and gram-positive cells. Specifically, the structure of the gram-positive basal body of flagella. And so, the basal bodies of the flagella in gram-positive cells actually consist of 2 complex protein rings, as we'll see down below in our image. And so, what you'll notice is that these two rings of the basal body are numbered down below right here. And the first ring of the basal body is the MS ring, whereas the second ring of the basal body is the C ring. And so the MS ring is this ring that you see right here, going around, from here to here. And the C ring is this other ring that's going around right here. And so, these two rings are the two rings that are found in the gram-positive basal body.

Now, in this image, just to orient you a little bit better, what you're looking at here is this is zoomed into the flagella. This is the flagella, the structure of the flagella, the flagella. And so, notice that up here what we have is the filament. Here what we have is the hook. And then, from here all the way down, what we have is the basal body. And notice that the basal body anchors the entire flagella to the actual bacterial cell. And so you can see the layers of the gram-positive cell here. The thick peptidoglycan layer is right here. Then you can see the periplasm, which is in between the peptidoglycan layer and the plasma membrane, and the plasma membrane is down below here. And so, the basal body extends all the way through those layers of the cell envelope. And these rings are important for helping to anchor the entire flagella to the cell. And once again, the two rings are the MS ring and the C ring. And we'll be able to compare these structures to the structures of the basal body in gram-negative cells in our future videos. But for now, this here concludes our lesson on the structure of the gram-positive basal body, and I'll see you all in our next video.

Structure of Gram-Negative Basal Body

In this video, we're going to talk about the structure of the flagella in gram-negative cells. Specifically, the structure of the gram-negative basal body. And so because gram-negative cells have an additional outer membrane that gram-positive cells do not have, the gram-negative cell basal bodies have to have additional protein rings to help anchor the flagella to the cell. And so instead of having just 2 protein rings in the basal body like what gram-positive cells have, gram-negative cells have 4 protein rings in the basal body. And so if we take a look at our image down below, notice on the far left over here, we're numbering all of the rings that are found in the basal body of gram-negative cells. Notice that the MS ring and the C ring are still present, and these are, pretty much the same as they were in the gram-positive cells. And really there's just 2 additional rings that are new here, that were not present in the gram-positive cell basal bodies. And so this is going to be the presence of the L ring and the presence of the P ring. And so the L ring, what you can see, is embedded right up here in the outer membrane itself. And again, this outer membrane is only found in gram-negative cells. Gram-positive cells do not have this outer membrane, and so they have no need for the L ring. Now the P ring, notice, is embedded here in the peptidoglycan layer, and partially in the periplasm as well. And recall that gram-negative cells have a very thin layer of peptidoglycan. And so the P ring is going to fit right into that layer. And so these are the 2 additional rings that are found in the gram-negative basal bodies that the gram-positive basal bodies do not have. And so this here, really concludes our lesson on the structure of the gram-negative basal body. And in our next lesson video, we'll be able to do a side-by-side comparison of the gram-negative and the gram-positive basal bodies. And so I'll see you all in our next video.

Which of the following is NOT a ring in the gram-negative cell basal body structure?

• A. MS-Ring
• B. C-Ring
• C. A-Ring
• D. P-Ring

Which of the following statements is TRUE?

• A. Gram-positive flagellar basal bodies have 4 protein rings.
• B. Gram-negative flagellar basal bodies have 2 protein rings.
• C. Gram-positive flagellar basal bodies have 2 protein rings.
• D. Gram-positive & gram-negative flagellar basal bodies have 4 protein rings.

Gram-Negative vs. Gram-Positive Basal Body Structure

In this video, we're going to do a side-by-side comparison of the basal body flagellar structure in gram-negative cells and in gram-positive cells. And so once again, due to the presence of an outer membrane in gram-negative cells, they actually require an additional 2 protein rings in the basal body that the gram-positive basal body does not have. And so if we take a look at our image down below, we'll be able to do a side-by-side comparison of the 2 basal bodies. And so, notice on the left-hand side over here, we're showing you the flagellar structure for gram-negative cells. And on the right-hand side over here, we're showing you the flagellar structure for gram-positive cells. And so, notice that because gram-negative cells have this additional outer membrane that the gram-positive cells do not have, the gram-negative cells require 2 additional protein rings in the basal body. And so taking a look at the basal body, which is extending right here in this region, notice that the gram-negative cells have to have the L ring, which is embedded in the outer membrane, and they have to have the P ring embedded in the peptidoglycan layer. And so those two rings are additional rings that are not found in gram-positive cells. And so, notice that the MS ring and the C ring are rings that are found in both the gram-negative and the gram-positive basal bodies. And so, really the difference between the two is focused around the addition of these two rings, the L ring and the P ring in the gram-negative cells. And so this here concludes our brief side-by-side comparison of gram-negative versus gram-positive basal body structure. And we'll be able to get some practice with these concepts as we move forward. So, I'll see you all in our next video.

Why do gram-negative flagellar basal bodies have an L-ring while gram-positive flagellar basal bodies do not?

• A. Gram-positive bacterial cells do not have an outer membrane where the L-ring is located.
• B. Gram-negative bacterial cells have larger flagella and require more basal body rings for support.
• C. Gram-negative bacterial cells have a thicker cell wall and require the L-ring for support.
• D. Gram-positive bacterial cells have a P-ring which performs the same functions as the L-ring in gram-negative cells.

Here’s what students ask on this topic:

What are the main components of a prokaryotic flagellum?

A prokaryotic flagellum consists of three main components: the filament, the hook, and the basal body. The filament is the primary structure made of the globular protein flagellin. The hook is a flexible, curved protein that connects the filament to the basal body. The basal body anchors the flagellum to the cell and consists of a rod and protein rings. In gram-positive bacteria, the basal body has two protein rings (MS and C rings), while in gram-negative bacteria, it has four rings (adding L and P rings) due to the presence of an outer membrane.

How does the basal body of a gram-positive flagellum differ from that of a gram-negative flagellum?

The basal body of a gram-positive flagellum consists of two protein rings: the MS ring and the C ring. In contrast, the basal body of a gram-negative flagellum has four protein rings: the MS ring, the C ring, the L ring, and the P ring. The additional L and P rings in gram-negative bacteria are necessary to anchor the flagellum through the outer membrane and the thin peptidoglycan layer, which are not present in gram-positive bacteria.

What is the function of the hook in a prokaryotic flagellum?

The hook in a prokaryotic flagellum serves as a flexible, curved protein that connects the filament to the basal body. Its primary function is to transmit the rotational force generated by the basal body to the filament, enabling the flagellum to rotate and propel the bacterial cell. The hook's flexibility allows it to act as a universal joint, ensuring smooth and efficient movement of the filament.

Why do gram-negative bacteria have additional protein rings in their basal body?

Gram-negative bacteria have additional protein rings in their basal body because they possess an outer membrane that gram-positive bacteria lack. The additional L and P rings in the basal body of gram-negative bacteria help anchor the flagellum through this outer membrane and the thin peptidoglycan layer. These extra rings provide the necessary structural support and stability for the flagellum to function effectively in the more complex cell envelope of gram-negative bacteria.

What is the role of the filament in a prokaryotic flagellum?

The filament is the primary component of a prokaryotic flagellum and is responsible for the actual movement of the bacterial cell. It is made of the globular protein flagellin and extends from the cell surface into the external environment. When the basal body rotates, it transmits this motion through the hook to the filament, causing the filament to rotate and propel the cell forward. The filament's structure and composition are crucial for efficient bacterial motility.