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

Prokaryotic motility, specifically swimming motility or flagellar motility, involves cell movement powered by the rotation of flagella. Cells exhibit a pattern of runs and tumbles; a run is smooth movement in one direction, while a tumble is an abrupt change in direction. This movement requires energy from a proton motive force (PMF). Understanding these mechanisms is crucial for grasping how bacteria navigate their environments and respond to stimuli, highlighting the importance of motility in microbial behavior and ecology.

Prokaryotic Flagellar Movement

In this video, we're going to begin our lesson on prokaryotic flagellar movement. Recall from our previous lesson videos that the term "motility" refers to the ability of an organism to move on its own. The term motility is directly related to movement. In this video, we will introduce a specific type of motility called swimming motility, which is also sometimes referred to as flagellar motility. Swimming motility and flagellar motility refer to the same thing. This is referring to the process of cell movement that's powered by the rotation of the flagella. In our previous lesson videos, we talked about movement that was powered by pili, but here we are talking about movement powered by flagella. When the flagella rotate in a specific direction, it will propel the cell through its environment and allow the cell to move through its environment. However, once the flagella start to rotate in the opposite direction, then the cell will stop moving and stop swimming as it once was.

Let's take a look at our image down below to get a better understanding of this. Here we're showing you how the rotational direction of the flagellum controls the swimming motility of a monotrichous cell, or a cell that has only one flagellum coming out of one pole of the cell. Notice below we're showing you a bacterial cell that has one flagellum and notice that it's rotating in a specific direction. Here, for example, we're saying that it's rotating in a counterclockwise direction just for the sake of this example. When the flagella rotate in one direction, it allows for cell movement, which is part of the swimming motility. You can see we have a little swimmer here to remind you that flagellar movement is referred to as swimming motility. The cell is going to continue to move until the flagella start to rotate in the opposite direction. Notice here we're saying a clockwise rotation is going to cause the cell to stop moving as it once was.

This here is really just the basics of prokaryotic flagellar movement, and we'll continue to learn more and more about it as we move forward in our course. So I'll see you all in our next video.

Runs and Tumbles

In this video, we're going to talk about how prokaryotic flagellar movement occurs in a series of runs and tumbles. A swimming cell that is moving using swimming motility or flagellar motility typically moves in a pattern of stop and go repeats that scientists call runs and tumbles. A run refers to a smooth swimming movement of the cell as the flagella rotate in a specific direction. A tumble refers to a random, abrupt change in direction as the flagella rotate in the opposite direction. If we take a look at the image below, we can get a better understanding of these runs and tumbles. Notice we show you the run and tumble method of a swimming motility by a peritrichous bacterial cell. You can see that it has flagella extending on regions that are all around the cell surface. When all of the flagella are coordinated and rotating in a counterclockwise direction (CCW), this allows for a run. The run is a smooth swimming movement of the bacterial cell in a specific direction. As soon as the flagella start to rotate in the opposite direction, in a clockwise direction (CW), a tumble occurs. The tumble is not associated with any net movement in a specific direction. Instead, the tumble just causes the cell to rotate and change directions. We emphasize that the tumble results in a change of direction. After the tumble, once the flagella coordinate and rotate back in a counterclockwise direction, another run occurs. This sequence is how prokaryotic flagellar movement works, alternating in a series of runs followed by tumbles, and then more runs and tumbles in a repetitive fashion. Like all other motors that power movement, the rotation of the flagella requires energy. The energy that powers prokaryotic flagellar movement comes in the form of what's known as a proton motive force (PMF). We will talk more about this proton motive force and how prokaryotic flagellar movement is powered as we move forward in our course. But for now, this concludes our brief lesson on runs and tumbles, and I'll see you all in our next video.

Movement in bacteria

• A. Is directly to or away from a stimulus.
• B. Relies on the beating of cilia.
• C. Is often referred to as run and tumble.
• D. May involve pili.
• E. Includes many types of movement that utilize pili and flagella.

"Tumbles"and straight-line "runs"are associated with:

• A. The action of fimbriae.
• B. How a pilus transfers DNA.
• C. Flagellar motility.
• D. Twitching motility.
• E. None of the above.

A bacteria can rotate its flagellum clockwise or counterclockwise. If the bacterial cell wants to stop swimming, which direction will it rotate its flagellum?

• A. Clockwise.
• B. Counterclockwise.
• C. To stop moving the bacterium will not rotate its flagellum at all.

Here’s what students ask on this topic:

What is prokaryotic flagellar movement?

Prokaryotic flagellar movement refers to the process by which prokaryotic cells, such as bacteria, move using their flagella. Flagella are long, whip-like appendages that rotate to propel the cell through its environment. This movement is powered by the rotation of the flagella, which can rotate in different directions to either move the cell forward (run) or change its direction (tumble). The energy required for this movement comes from a proton motive force (PMF), which is generated by the flow of protons across the cell membrane.

How does the direction of flagellar rotation affect bacterial movement?

The direction of flagellar rotation plays a crucial role in bacterial movement. When the flagella rotate counterclockwise (CCW), they bundle together and propel the cell forward in a smooth, linear motion called a 'run.' Conversely, when the flagella rotate clockwise (CW), they splay apart, causing the cell to undergo a 'tumble,' which is an abrupt, random change in direction. This alternating pattern of runs and tumbles allows bacteria to navigate their environment effectively.

What is the role of proton motive force (PMF) in flagellar movement?

The proton motive force (PMF) is essential for powering flagellar movement in prokaryotes. PMF is generated by the flow of protons (H⁺) across the cell membrane, creating an electrochemical gradient. This gradient provides the energy needed for the rotation of the flagella. As protons flow back into the cell through the flagellar motor complex, they drive the rotation of the flagella, enabling the cell to move. Without PMF, the flagella would not have the energy required to rotate and propel the cell.

What are runs and tumbles in bacterial movement?

Runs and tumbles are the two main components of bacterial movement. A 'run' is a smooth, linear movement in a specific direction, driven by the counterclockwise rotation of the flagella. During a run, the flagella bundle together, propelling the cell forward. A 'tumble' is an abrupt, random change in direction, caused by the clockwise rotation of the flagella. During a tumble, the flagella splay apart, causing the cell to reorient itself. This alternating pattern of runs and tumbles allows bacteria to explore their environment and respond to stimuli.

How do bacteria use flagella to navigate their environment?

Bacteria use their flagella to navigate their environment through a series of runs and tumbles. During a run, the flagella rotate counterclockwise, propelling the cell forward in a smooth, linear motion. When the cell needs to change direction, the flagella rotate clockwise, causing a tumble. This abrupt change in direction allows the cell to reorient itself. By alternating between runs and tumbles, bacteria can move toward favorable conditions (e.g., nutrients) or away from harmful stimuli (e.g., toxins), effectively navigating their environment.