Functions of flagella

Introduction

Flagella are microscopic hair-like structures that allow a cell to move. “Flagellum” is a Latin word that means “whip”. Flagella are whip-like structures that help push a cell through fluids. Only a few species use flagella as sensory organs to detect pH and temperature changes. Archaea, bacteria, and eukaryotes all have filamentous structures. 

Archaeal flagella

Flagella of archaea are nonhomologous. 

Bacterial flagella

Bacterial flagella are a coiled, thread-like structure with a sharp bend and a rotary motor at its base, made up of the protein flagellin. Between a hook and a basal body, a shaft passes through the cell membrane’s protein rings. 

Eukaryotic flagella

Eukaryotic flagella are complex cellular appendages seen in protist cells, plant gametes, and animals that pound backwards and forwards. It is made up of tubulin, a protein. 

Bacterial flagella structure

There are three elements to the flagella structure: 

1. Basal body

2. Hook 

3. Filament

Basal body

It is connected to both the cell membrane and the cytoplasmic membrane. It is made up of rings that are encircled by a pair of proteins known as MotB. Among the rings are: 

• L-ring: An outer ring found in Gram +ve bacteria that is anchored in the lipopolysaccharide layer. 

• P-ring:  peptidoglycan layer anchors the P-ring. 

• C-ring: The C-ring is a cytoplasmic ring. 

• M-S ring: The cytoplasmic membrane anchors the M-S ring. 

Hook

Connects the filament to the base motor protein. In Gram +ve bacteria, the hook length is longer. 

Filament

A thin hair-like structure emerges from the hook called filament. 

Types of flagella

Flagella are of 4 types:

Monotrichous

At one end or the other, a single flagellum. Polar flagellum can revolve in both clockwise and counterclockwise directions. The organism goes forward when it rotates clockwise, whereas it moves backwards when it rotates anti-clockwise. 

Peritrichous

Several flagella are attached to the organism’s surface. Because they are present everywhere around the organism, these are not polar flagella. These flagella rotate in the opposite direction of the organism, forming a bundle that propels the organism in one direction. When some of the flagella break and start revolving clockwise, the organism stops moving and starts tumbling. 

Lophotrichous

At one end of the organism or the other, there are many flagella. Polar flagellum can revolve in both clockwise and counterclockwise directions. The organism goes forward when it rotates clockwise, whereas it moves backwards when it rotates anti-clockwise. 

Amphitrichous

On both ends of the organism, there is a single flagellum. Polar flagellum can revolve in both clockwise and counterclockwise directions. The organism goes forward when it rotates clockwise, whereas it moves backwards when it rotates anti-clockwise. 

Function of flagella

The flagellum is a motility organelle that enables chemotaxis and movement. Bacteria can have one or more flagella, and they can be either polar (with one or more flagella in one site) or peritrichous (with one or more flagella in various locations) (several flagella all over the bacterium). Flagella, in addition to movement, have a variety of different roles that vary between bacteria and throughout the bacterial life cycle: a flagellum can assist in biofilm formation, protein export, and adhesion, for example. 

Flagella are the principal motility structures of many bacteria, allowing them to travel towards the most favourable environment. Bacteria move in reaction to a variety of stimuli, allowing them to adapt to changing environmental conditions. Flagella are required for motility and, eventually, fertilisation in eukaryotic cells such as sperm.

Flagella serve a critical function in the colonisation of tissue surfaces as a virulence factor for invading and developing within host tissue. These are also necessary for non-pathogenic colonisation of surfaces such as plants, soil, and animals.

Flagella are engaged in nutrition and waste exchange in some bacteria by disrupting the organism’s nutrient-poor, waste-rich shell. Flagella in alkaliphilic bacteria are sodium-driven, allowing sodium to reenter the cytoplasm and maintain a neutral cytoplasmic pH. 

Conclusion

They aid in the movement of an organism. Temperature and pH variations are detected by them as sensory organs. Flagella are also utilised as a secretory organelle, according to recent studies. In Chlamydomonas, for example.