Flagella types

A flagellum, also known as a flagella, is a lash or hair-like structure found on the cell body that is vital for the cell’s various physiological tasks. The term ‘flagellum’ comes from the Latin word for whip, referring to the flagellum’s long, slender construction, which resembles a whip. Flagella are found in a variety of microscopic and macroscopic species, including bacteria, fungi, algae, and mammals, and are distinctive of the protozoan group Mastigophora. 

Structure of flagellum:

Prokaryotes and eukaryotes have various flagella size structures and numbers. The bacterial flagellum differs from the archaeal flagellum even among prokaryotes. Flagella formation also has a variety of compositions and mechanisms. The basic structure of a flagellum, on the other hand, comprises of several structures that are seen in all domains of life. The following are the components of a flagellum’s basic structure: 

Filament:

The filament is the most visible portion of a flagellum, accounting for nearly all of the flagellum’s structures. Outside of the cell membrane, filaments can be seen using flagellar staining methods. The filaments’ mobility is controlled by a motor located in the cytoplasm.

Hook or anchoring structures:

The flagellar hook is a curved, small tubular structure that connects the flagellar motor or the basal body to the long filament. The hook is made up of several hook protein subunits that come together to form polymorphic supercoil structures. 

Basal body or motor device:

A flagellum’s basal body is the only part of the flagellum that is visible through the cell membrane. It is attached to the flagellum’s hook, which links to the long filament. The basal body is a rod-like structure with a microtubule ring system. Diverse types of cells have different basal body components. 

Flagella formation mechanism:

The flagellum is made up of a complex membrane and structures that are made up of many proteins and their connections. The following is a summary of the flagella production and assembly process: 

Formation of the basal body:

The process starts with the cytoplasmic inclusion of FliF, an integral protein containing an MS-ring. The MS-ring is crucial because it controls how a flagellum’s other structures are put together. 

Formation of the hook:

The protein FlgD, which is absent in finished flagella, causes hook development. The rod cap protein is replaced by hook capping proteins as hook assembly begins. The FlgD protein is required for the polymerization of subunits into a -helical structure. 

Filament assembly:

The filament monomers are assembled in the presence of the HAP2 pentamer complex, which caps the distal end of the filaments as they are constructed. The cap is required to inhibit subunit diffusion from the filament and to provide a conformational shift that allows polymerization to occur. 

Types of flagella:

Bacterial flagella:

The flagella of bacteria are helically coiled structures that are slightly longer than those of archaea and eukaryotes. Flagella in prokaryotes are thinner than those in eukaryotes. The number of flagella in bacteria varies depending on which species are involved in movement. 

Archaeal flagella:

The flagellum of archaea is a distinct motility apparatus that differs in composition but is assembled similarly to the flagellum of bacteria. The proteins in the flagella are organised in a right-handed helix, which causes the flagella to rotate clockwise. 

Eukaryotic flagella:

In terms of architecture, composition, mechanism, and assembly, eukaryotic flagella differ from bacterial flagella. Eukaryotic flagella are made up of hundreds of different proteins, whereas bacterial flagella are made up of only roughly 30. 

Movement of bacterial flagella:

Despite the structural diversity of bacterial flagella, flagellated bacteria have a common rotary nanomachine, the flagellar motor, which is positioned near the filament’s base. The flagellar motor is made up of a rotor ring complex and several transmembrane stator units, and it converts ion flux via each stator unit’s ion channel into the mechanical work required to rotate the motor. Intracellular chemotactic signalling pathways control the direction of flagella-driven motility in response to environmental changes, allowing bacteria to move to more favourable habitats. 

Conclusion:

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.