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

DefinitionFlagella 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.
StructureFlagella are Whip like, helical, but not straight structure.Pili are Hair like, non-helical and straight structures.
LengthThese are long and whip-like.These are short and hair-like.
ThicknessFlagella are thicker than pili, 15-20 nm in diameter.These are thin, about 3-10 nm in diameter.
NumberFew flagella occur per cell.Numerous pili occur per cell.
OriginOriginate from the cell wall.Originate from the cytoplasmic membrane.
Occurrenceflagella can occur either polar, lateral or peritrichous.They occur throughout the surface of the cell.
Found inThey are found in gram positive and gram negative bacteria.Tey are only found in gram negative bacteria.
Attached to cell wallNoyes
ConjugationNot required for conjugationRequired for conjugation.
Compositioncomposed of flagellin protein.composed of pilin protein.
TypesThree types of flagella occur in nature: bacterial, archaeal and eukaryotic.Two types of pili are found: conjugative and type IV.
FunctionResponsible 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
MotionFlagella exhibit an undulating, sinusoidal motion.A twitching motility is shown by type IV pili.
SizeLong about 15 µmShort about 0.2-20 µm
RigidityMore rigidComparatively less rigid
Motor systemPresent in flagella.Absent in pili
Organ of adhesionOrgan of adhesion absent in flagella.Organ of adhesion present in pili.
Receptors of virusAbsent in flagellaThese acts as receptors of different viruses
ExamplesFlagella occur in Salmonella.Pili occur in Pseudomonas.
flagella vs pili



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