[Biology Class Notes] on Flagella Pdf for EXAM

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:

1. Atrichous: There is no flagellum.
   Example: Lactobacillus 

2. Monotrichous:
   Single polar flagellum can rotate both clocks and anti-clockwise resulting in forwarding movement and backward movement respectively.
   Example: Vibrio cholerae

3.  Amphitrichous:
   One flagellum is present on each end. Movements are like monotrichous flagella.
   Example: Alkaligens faecalis

4. Lophotrichous:
   Tufts of flagella present at one or both sides. Propagates clockwise and anticlockwise.
   Example: Spirillum

5. Peritrichous:
   Numerous flagella are present all over the bacterial body, anticlockwise rotation produces one-directional movement.
   Example: Salmonella Typhi

6. 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: