Prokaryotic Motility: Videos & Practice Problems

Chemotaxis is the movement of motile cells towards a chemoattractant and away from chemorepellants, with positive chemotaxis indicating movement towards a favorable chemical and negative chemotaxis indicating movement away from an unfavorable one. Phototaxis, a specific type of chemotaxis, involves movement towards or away from light. Cells navigate through a series of runs and tumbles, resulting in non-linear paths. Understanding these mechanisms is crucial for grasping how cells interact with their environment and respond to stimuli.

Chemotaxis

Chemotaxis is a fundamental biological process defined as the movement of a cell toward a chemoattractant and away from a chemorepellant. A chemoattractant is a chemical substance that attracts motile cells, leading to what is known as positive chemotaxis. Conversely, a chemorepellant is a chemical that repels motile cells, resulting in negative chemotaxis as cells move away from it.

In addition to chemotaxis, there is a specific type called phototaxis, which refers to the movement of cells toward or away from light. When cells move toward light, it is termed positive phototaxis, while movement away from light is referred to as negative phototaxis.

Cells utilize their flagella to navigate these chemical gradients, powered by energy derived from the proton motive force (PMF). The movement of cells in response to these stimuli is not linear; instead, cells exhibit a pattern of movement characterized by runs and tumbles. This means that while cells may generally move toward favorable conditions, their path is not a straight line but rather a series of directional changes.

Understanding chemotaxis is crucial for comprehending how cells interact with their environment, allowing them to seek out nutrients or evade harmful substances. This process plays a vital role in various biological functions, including immune responses and microbial behavior.

Structures external to the bacterial cell wall that is used for motility (movement) by chemotaxis:

• A. Endospores
• B. Capsules
• C. Flagella
• D. Pili
• E. Ribosomes

Answer: (C)

A bacterial cell moving away from the light would be an example of _______.

• A. Positive phototaxis
• B. Negative phototaxis
• C. Positive chemotaxis
• D. Negative chemotaxis

Answer: (B)

Introduction to Prokaryotic Flagella

Prokaryotic flagella, which differ from eukaryotic flagella, play a crucial role in the motility of bacterial cells. The term "flagella" is the plural form, while "flagellum" refers to a single structure. These flagella are long, filamentous surface proteins that enable cells to propel themselves through their environment, facilitating movement.

A group of flagella on a bacterial cell is known as a "tuft." This arrangement allows for coordinated movement, acting like a propeller to drive the cell in a specific direction. The distribution of flagella can vary significantly across different bacterial species, influencing their motility patterns.

Understanding the structure and function of prokaryotic flagella is essential for comprehending how bacteria navigate their surroundings. As we delve deeper into this topic, we will explore the various mechanisms and adaptations that enhance bacterial motility.

Prokaryotic Flagellar Structure

Prokaryotic flagella are essential structures that enable movement in prokaryotic organisms, such as bacteria. They consist of three main components: the filament, the hook, and the basal body, each playing a crucial role in the flagellum's function.

The filament is the primary part of the flagellum, composed of the globular protein flagellin. This long, whip-like structure is responsible for the actual propulsion of the cell. In diagrams, the filament is often represented in blue, highlighting its significance as the main driving force behind flagellar movement.

Next, the hook serves as a flexible connector between the filament and the basal body. This curved protein allows for the rotation of the filament, which is essential for the flagellum's function. The hook is typically depicted in green in illustrations, emphasizing its role in linking the filament to the basal body.

Finally, the basal body is the anchor of the flagellum, embedded within the cell membrane. It consists of a rod and a series of protein rings that secure it to the cell envelope. The basal body is crucial for the flagellum's stability and function, as it provides the necessary support for the rotation mechanism that propels the cell forward.

In summary, the structure of prokaryotic flagella is a well-coordinated assembly of the filament, hook, and basal body, each contributing to the overall motility of prokaryotic cells. Understanding these components is fundamental to grasping how bacteria navigate their environments.

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

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

Answer: (C)

Here’s what students ask on this topic:

What is chemotaxis and how does it work in prokaryotic cells?

Chemotaxis is the movement of motile cells towards a chemoattractant and away from chemorepellants. In prokaryotic cells, this process is driven by the energy from a proton motive force (PMF). When a cell detects a favorable chemical (chemoattractant), it moves towards it, a process known as positive chemotaxis. Conversely, when a cell detects an unfavorable chemical (chemorepellant), it moves away, known as negative chemotaxis. The movement is not in a straight line but involves a series of runs and tumbles, allowing the cell to navigate its environment effectively.

What is the difference between positive and negative chemotaxis?

Positive chemotaxis refers to the movement of motile cells towards a favorable chemical, known as a chemoattractant. This movement is driven by the cell's desire to reach a more favorable environment. Negative chemotaxis, on the other hand, is the movement of motile cells away from an unfavorable chemical, known as a chemorepellant. This helps the cell avoid harmful or less favorable conditions. Both types of chemotaxis are crucial for the survival and adaptation of cells in varying environments.

How do prokaryotic cells move towards or away from light?

Prokaryotic cells move towards or away from light through a process called phototaxis, which is a specific type of chemotaxis. When a cell moves towards light, it is referred to as positive phototaxis. Conversely, when a cell moves away from light, it is called negative phototaxis. This movement is facilitated by the cell's flagella, which are powered by the proton motive force (PMF). The cell's movement involves a series of runs and tumbles, allowing it to navigate towards or away from light sources effectively.

What role do runs and tumbles play in the movement of prokaryotic cells?

Runs and tumbles are crucial for the movement of prokaryotic cells. A 'run' is a straight-line movement, while a 'tumble' is a random reorientation of the cell. These alternating movements allow the cell to navigate its environment. During chemotaxis, the frequency and duration of runs and tumbles are adjusted based on the presence of chemoattractants or chemorepellants. This non-linear path enables the cell to effectively move towards favorable conditions or away from unfavorable ones, ensuring its survival and adaptation.

What is the proton motive force (PMF) and how does it relate to prokaryotic motility?

The proton motive force (PMF) is an electrochemical gradient generated by the movement of protons (H⁺) across the cell membrane. This gradient creates potential energy that can be harnessed by the cell for various functions, including motility. In prokaryotic cells, the PMF powers the rotation of flagella, which are the structures responsible for cell movement. By utilizing the energy from the PMF, prokaryotic cells can move towards favorable environments (positive chemotaxis) or away from unfavorable ones (negative chemotaxis).