Flagella are microscopic hair-like structured organisms that help in the movement of a cell and are mostly unicellular. Flagella actually means “whip” because of its whip-like appearance that helps to propel a cell through fluids. In this article on flagella, students will learn about the basics of flagella, the functions, and the structure as well as types of flagella.
Flagella
A flagellum has a 15-20nm diameter and can be seen under a light microscope. The whip-like structure of flagella facilitates movement in certain single-celled organisms. These are filamentous structures made up of microtubules. They are usually found in eukaryotes and bacteria.
Types of Flagella
There are 6 types of flagella:
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Atrichous: There is no flagellum.
Example: Lactobacillus
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Monotrichous:
Single polar flagellum can rotate both clocks and anti-clockwise resulting in forwarding movement and backward movement respectively.
Example: Vibrio cholerae -
Amphitrichous:
One flagellum is present on each end. Movements are like monotrichous flagella.
Example: Alkaligens faecalis -
Lophotrichous:
Tufts of flagella present at one or both sides. Propagates clockwise and anticlockwise.
Example: Spirillum -
Peritrichous:
Numerous flagella are present all over the bacterial body, anticlockwise rotation produces one-directional movement.
Example: Salmonella Typhi -
Cephalotrichous: several flagella are present at both ends. Movements are similar to monotrichous flagella.
Example: Pseudomonas
Parts of Flagella
The flagella are helical in structure and composed of flagellin protein or globular protein. The body of flagella is divided into three parts:
The basal body consists of a rod and a series of rings that are attached to the cell wall and the cytoplasmic membrane. It consists of rings which are basically proteins. There are three types of rings, namely the L-ring attached to the lipopolysaccharide, the P-ring attached to the peptidoglycan layer, and the M-S ring which is attached to the cytoplasmic membrane.
The hook is a flexible connection between the filament and the basal body proteins.
The filament is a rigid, helical structure that extends from the cell surface. It has a hair-like structure.
Functions
A flagellum also has some functions in eukaryotes and bacteria alike. They can be stated as follows: