Movement of Flagella

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. Flagella serve as a motility organelle in various species, as well as aiding in food collection and circulation. 

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 diameter is estimated to be roughly 20 nanometers.

The number of flagella in bacteria varies depending on which species are involved in movement. Flagella can operate as sensory structures in some situations, detecting changes in the environment.

The filaments are longer than those of archaea and have a left-handed helix with swimming motility as a result of counter-clockwise movement, therefore the length of the flagella could be different. 

Archaeal flagella

The flagellum of archaea is a distinct motility apparatus that differs in composition but is assembled similarly to the flagellum of bacteria. Flagella can be found in practically all of the domains, including halophiles, methanogens, and thermophiles.

The diameter of archaeal flagella differs from that of bacterial flagella because archaeal filaments are thinner. The proteins in the flagella are organised in a right-handed helix, which causes the flagella to rotate clockwise. As the cell rotates clockwise, the speed of the archaeal flagella increases.

The hooks of archaeal flagella vary in length from species to species, unlike those in bacteria. Several studies have also shown that the switching mechanism and sensory control of archaeal flagella differ from those of bacterial flagella. 

Eukaryotic flagella

Flagella are found in many algae and some animal cells, such as sperm, in eukaryotes. Flagella in eukaryotic animals are largely related with cell movement, cell nutrition, and reproduction. These also serve as sensory antennae in some algae.

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.

Similarly, eukaryotic flagella are propelled by restricted dynein-dependent microtubules sliding, but bacterial flagella are propelled by a rotational motor located near the basal body.

Eukaryotic flagella are made up of microtubule-based centrioles from which the proteins that make up the axoneme are targeted. A eukaryotic cell’s centriole is frequently referred to as the flagella’s basal body. 

Movement of flagella

Most flagellate protozoans have one or two flagella that extend from the body’s anterior (front) end. However, certain protozoans have many flagella that are dispersed throughout the body; in these circumstances, the flagella are frequently united into discrete clusters. Planar waves, oarlike beating, or three-dimensional waves are all examples of flagellar locomotion. All three types of flagellar locomotion rely on contraction waves that travel from the base to the tip of the flagellum, or the other way around, to propel the flagellum forward or backward. 

Cilia

Cilia are small, slender hair-like projections on the surfaces of all mammalian cells. They are primitive in character and can be solitary or in groups. Cilia are important for movement. They have a role in mechanoreception as well. Ciliates are organisms that have cilia on their skin. 

Movement of cilia

The hair-like outgrowths on the plasma membrane are known as cilia. The rhythmic movement of cilia that creates fluid or cell movement is known as ciliary movement. In Paramoecium, for example, ciliary movement aids in cell movement as well as food flow within the cell. Cilia are located in the epithelial lining of the fallopian tube and the respiratory system, where they help with fluid circulation and trap foreign particles in mucus. Cilia and flagella have a microtubule-based cytoskeleton. They have an axoneme core with 9 doublets of microtubules on the perimeter and a pair of microtubules in the middle. Microtubules connected with the dynein arms slide, causing ciliary movement. 

Conclusion

The dynein arms push on the adjacent outer doublets, creating a sliding movement between them, using ATP produced by mitochondria near the base of the cilium or flagellum as fuel. Sliding is transformed to bending because the arms are activated in a tight sequence both around and along the axoneme, and the quantity of sliding is limited by the radial spokes and inter-doublet linkages.