The bacterial flagella



The bacterial flagella are composed of the protein flagellin. Its shape is a 20 nanometer-thick hollow tube. It is helical in shape and has a sharp bend just outside of the outer membrane. This “hook” allows the helix to point directly away from the cell. A shaft runs between the hook and the basal body, passing through protein rings in the cell’s membrane that act as bearings.

Gram-positive organisms have 2 of these basal body rings. One in the peptidoglycan layer and one in the plasma membrane. Gram-negative organisms have 4 such rings. The L ring associates with the lipopolysaccharides. The P ring associates with the peptidoglycan layer. The M ring is embedded in the plasma membrane. The S ring is directly attached to the plasma membrane. The filament ends with a capping protein.

The rotor transports protons alone can operate at 6,000 to 17,000 rpm. With the flagellar filament attached usually only reaches 200 to 1000 rpm.

The components of the bacterial flagellum

The components of the bacterial flagellum are capable of self-assembly without the aid of enzymes or other factors. Both the basal body and the filament have a hollow core. The component proteins of the flagellum are able to move into their respective positions. During assembly, protein components are added at the flagellar tip rather than at the base.

The basal body has several traits in common. Within some types of secretory pores, such as the hollow rod-like “plug” in their centers. It extends out through the plasma membrane.

Types of Flagella

Different species of bacteria have different numbers and arrangements of flagella. Monotrichous bacteria have a single flagellum (e.g., Vibrio cholerae). Similarly, Lophotrichous bacteria have multiple flagella. They are located at the same spot on the bacteria’s surfaces. They act in concert to drive the bacteria in a single direction. Amphitrichous bacteria have a single flagellum on each of two opposite ends. Only one flagellum operates at a time. Because of this, the bacteria to reverse course rapidly by switching which flagellum is active. Peritrichous bacteria have flagella projecting in all directions (e.g., Escherichia coli).

Some species of bacteria (such as Spirochetes) have a specialized type of flagellum. They are called an “axial filament”. As a result, it causes the entire bacterium to move forward in a corkscrew-like motion.

Movement of Bacteria

Counterclockwise rotation of monotrichous polar flagella thrust the cell forward. Because of this, the flagella trailing behind. Periodically, the direction of rotation is briefly reversed. Because of this, it causes a “tumble”. As a result of this, the cell seems to thrash about in place. Above all, it results in the reorientation of the cell. When moving in a favorable direction, “tumbles” are unlikely. However, when the cell realizes that its direction of motion is unfavorable (e.g., away from a chemical attractant), a tumble may occur. Because of this, the chance that the cell will be thus reoriented in the correct direction.

Bacterial flagella consist of a hollow, rigid cylinder. For instance, it is composed of a protein called flagellin. Similarly, it forms a filament anchored to the cell by a curved structure called the hook. As discussed earlier, the hooks attaches the basal body to filaments. Flagellae are, in effect, rotary motors comprising a number of proteinaceous rings embedded in the cell wall.

In chemotaxis, the bacteria can sense nutrient molecules such as sugars or amino acids and move towards them. Additionally, they can also move away from harmful substances such as waste products and in response to temperature, light, gravity, etc.

Process of Bacterial Motility:

Flagella provides bacterial motility. It has helical-shape structures. However, it projects from the surface of the cell. After that, the filament of the flagellum is built up from multiple copies of the protein flagellin. Where the filament enters the surface of the bacterium, there is a hook in the flagellum. Similarly, this is attached to the cell surface by a series of complex proteins called the flagellar motor. Above all, this rotates the flagellum. Because of this, it causes the bacterium to move through the environment. Above all, the numbers and distribution of flagella vary with bacterial species. Some have a single, polar flagellum, whereas others are flagellate over their entire surface (peritrichous); intermediate forms also exist.

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