Flagella Structure: Detailed Component Wise Structure

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Flagella aids in the motility or locomotion or movement of the organisms. It is adhered to the surface of the cell preferably to the cell membrane or cytoplasm and promotes motility.

The flagella structure is simple in prokaryotes and it has basically three parts in them. In the case of eukaryotes they are complex in structure but the ultimate role of flagella remains the same in all flagellated organisms.

Flagella structure in Bacteria:

The flagella has a spiral or helical morphology that comprises proteins called the flagellin protein in bacteria.

The flagella structure is separated into three parts:

flagella structure
A flagellated cell (tail)
Image credits- Pixabay

Basal Body

Basal Body is the region that is adhered to the cell membrane or cytoplasmic membrane or to the outer membrane of the cell basically. 

It consists of ring- like structures which are closely packed by proteins in pairs called MotB. 

The rings are

  • L-ring: L- ring is the outer or the exterior ring attached in the exterior lipo-polysaccharide layer, which are mostly found in gram positive bacteria.
  • P-ring: Attached in the peptidoglycan layer of the cell.
  • C-ring: Attached in the cytoplasm of the cell.
  • M-S ring: Attached in the cytoplasmic membrane of the cell.

Filament

  • The minute hair strand-like structure that comes out from the hook region.

Hook

  • The hook is a wider region that is present at the end of the filament.
  • It connects the filament to the protein in the tip or base. 
  • Gram positive bacteria have longer hooks in comparison with others.
flagella structure
Basal body- Flagella
Image credits- Wikimedia

Eukaryotic flagella structure:

We know that eukaryotic organisms are complex in structures.

Characteristics of Eukaryotic flagella structure:

  • The flagella structures of the eukaryotic are larger and complex by nature. 
  • The eukaryotic flagella are surrounded by a cell membrane for protection.
  • The eukaryotic flagella are made up of tubulins.
  • The locomotion in eukaryotic flagella is driven by the ATP that is produced by the membrane bound mitochondria- the powerhouse of the cell.
  • The locomotory mechanisms in eukaryotic flagella are called the bending movement or mechanisms as they move in the bending motion (S shaped).
  • In eukaryotes, the flagella is subjected to a 9+2 arrangement of microtubules.
  • The best example for eukaryotic flagellated structure is Sperm Cell.

Read More on Eukaryotic cell Vs Bacterial cell

Flagella filament structure:

  • The flagella basically have 3 parts in them- the basal body, filament and hook.
  • The flagella filament structures are stiff in nature. 
  • They are made up of complex amino acid structures, that is they are made up of protein.
  • Though flagella is considered to have minute thread like structures they have a hollow core in them.
  • The filament has a cap protein at the terminal part which is called as FliD.
  • When the cap protein is absent in the cell, they fail to develop the flagella and remain as an impaired locomotion cell.

Flagella internal structure:

The prokaryotic flagella is so simple in structure but when it comes to eukaryotic flagella, it is complex in nature.

The flagella internal structure in eukaryotes has the axoneme.

Cross section of axoneme:

  • Axoneme has 2 types of tubules in 9+2 fashion, that is 9 pairs of tubules.
  • One tubule is the locomotory and the Second one is the B tubule which is called the doublet microtubule.
  • In the core region that is the middle region there are 2 tubules which are not in pair. It is called the central microtubule that is attached to the inner sheath.

Chlamydomonas Flagella Structure:

Chlamydomonas is a single celled green algae which lives in water and moist spots.

Chlamydomonas has 2 flagella for swimming. It is called the apical flagella as it is present on the upper surface in the cervical spine. It originates from the basal grain located in the cytoplasm of the cell.

E. coli flagella structure:

Escherichia coli or also called E.coli is a gram-negative bacterium commonly found on the lower intestines of certain animals.

E. coli is said to have Peritrichous flagella.

Bacterial flagellate configurations 2
Bacterial flagella
Image credits- Wikimedia

Peritrichous flagella

When the flagellum is present all over that is present fully on the surface of the cell, it comes under the category of Peritrichous flagella.

It has

Basal Body

  • Basal Body of E. coli is the region that is adhered to the cell membrane or cytoplasmic membrane or to the outer membrane of the E. coli cell basically. 
  • The basal body of E. coli consists of ring- like structures which are closely packed by proteins in pairs called MotB. 

The details on these rings are already discussed in this article.

The rings are L- ring, P-ring, C- ring, M-S ring.

Filament

The minute hair strand-like structure that comes out from the hook region.

Hook

  • The hook is a wider region that is present at the end of the filament.
  • It connects the filament to the protein in the tip or base. 

The flagella in E.coli is one of the responsible factors for its virulence factor.

OSC Microbio 03 03 BaFlagella
Flagella structure of Gram Positive and Gram Negative bacteria
Image credits- Wikimedia

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