20 Differences Between Pili And Flagella

What is Flagella?

Flagella also known as flagellum, which is a lash-like appendage, emerges from the cell body of cells known as flagellates. One cell can contain one or several flagella. This hair-like structures helps in locomotion of a cell. It has a whip-like appearance which propel a cell through the liquid. Some organisms used flagella as a sensory organs which can detect alteration in pH and temperature.

This filamentous structures mainly found in archaea, bacteria, and eukaryotes. The Archaeal flagella are nonhomologous, while the Bacterial flagella are a coiled, thread-like structure, sharp bent, composed of a rotary motor at its base and are consist of the protein flagellin. The flagella of eukaryotic cells are complicated cellular projections that pummel backwards and forward and are found in protist cells, gametes of plants, and animals. The tubulin protein is the main component of eukaryotic flagella.

The helical structure of flegells is composed of flagellin protein. The flagella is made of three parts such as Basal body, Hook, and Filament.

What is Pili?

Pili also known as pilus, it is a hair-like appendage occurs on the surface of many bacteria and archaea. These are mainly found in gram-negative bacteria. Pili is originated from the plasma membrane and its made of pilin protein. The length of a pill is ranges from 0.5- 2 um and the diameter ranges from 5-7. There are two types of Pili such as short attachment pili and long conjugation pili. The short one is known as fimbriae and the long one is known as “F” or sex pili.

Differences between Pili and Flagella/ flagella vs pili

Characters	Flagella	Pili
Definition	Flagella are long, whip like, helical appendages that protrude through the cell membrane.	Pili are hallow, non-helical, filamentous appendages that protrude from the surface of cell.
Structure	Flagella are Whip like, helical, but not straight structure.	Pili are Hair like, non-helical and straight structures.
Length	These are long and whip-like.	These are short and hair-like.
Thickness	Flagella are thicker than pili, 15-20 nm in diameter.	These are thin, about 3-10 nm in diameter.
Number	Few flagella occur per cell.	Numerous pili occur per cell.
Origin	Originate from the cell wall.	Originate from the cytoplasmic membrane.
Occurrence	flagella can occur either polar, lateral or peritrichous.	They occur throughout the surface of the cell.
Found in	They are found in gram positive and gram negative bacteria.	Tey are only found in gram negative bacteria.
Attached to cell wall	No	yes
Conjugation	Not required for conjugation	Required for conjugation.
Composition	composed of flagellin protein.	composed of pilin protein.
Types	Three types of flagella occur in nature: bacterial, archaeal and eukaryotic.	Two types of pili are found: conjugative and type IV.
Function	Responsible for motility and also functions as a sensory organs which can detect alteration in pH and temperature.	Responsible for attachment during conjugation and also helps in motility
Motion	Flagella exhibit an undulating, sinusoidal motion.	A twitching motility is shown by type IV pili.
Size	Long about 15 µm	`Short about 0.2-20 µm`
Rigidity	More rigid	Comparatively less rigid
Motor system	Present in flagella.	Absent in pili
Organ of adhesion	Organ of adhesion absent in flagella.	Organ of adhesion present in pili.
Receptors of virus	Absent in flagella	`These acts as receptors of different viruses`
Examples	Flagella occur in Salmonella.	Pili occur in Pseudomonas.