STRUCTURAL ORGANISATION OF CILIA AND FLAGELLA- IN PROKARYOTES AND EUKARYOTES TYPES OF FLAGELLA

1. Dr. Manikandan Kathirvel M.Sc., Ph.D., (NET)
Assistant Professor,
Department of Life Sciences,
Kristu Jayanti College (Autonomous),
(Reaccredited with "A++" Grade by NAAC)
Affiliated to Bengaluru North University,
K. Narayanapura, Kothanur (PO)
Bengaluru 560077
Mobile: 9624060194/
STRUCTURAL ORGANISATION OF CILIA AND FLAGELLA-
IN PROKARYOTES AND EUKARYOTES
TYPES OF FLAGELLA

2. Cilia

3. Cilia
• Cilia are small, slender, hair-like structures present on the surface of all mammalian cells.
• Cilia are microscopic, hair-like structures that project from the surface of many eukaryotic cells.
• The organelle cilia are found in eukaryotic cells.
• Cilia are membrane-bound structures with their membrane being continuous with the plasma membrane.
• Unlike the plasma membrane of cells, ciliary membrane has been shown to contain distinct lipids and proteins.
• They are primitive in nature and could be single or many.
• They can be of two types – motile cilia and non-motile cilia.
• The non-motile cilia are known as primary cilia and act as sensory organelles.
• Cilia are structurally identical to flagella.
• Prokaryotes (bacteria) do not have cilia
• Cilia play a major role in locomotion.
• They are also involved in mechanoreception.
• The organisms that possess cilia are known as ciliates.
• They use their cilia for feeding and movement.
Depending on the type of cells, cilia and flagella have the following functions:
• Propelling cells - Using cilia or flagella, cells are able to move freely in their
environment, especially in aquatic or moist environments.
• Sensory functions - Some cilia and flagella allow cells to sense changes in
their surroundings which in turn allows the cells to respond appropriately.
• Transporting material - Some cells are able to not only trap, but also guide the
transportation of given material. This may serve to engulf such material into the
cell or prevent unwanted material/particles/microorganisms from invading the
cell or tissue.
Cilia of respiratory tract

4. Types of Cilia
Following are the two different types of cilia:
Motile Cilia
These are found in large numbers on the surface of the cell. In humans, these are found in the respiratory
epithelium of the respiratory tract. Here, they function by clearing the mucus and dust out of the lungs.
• Motile cilia (9+2) can be found in both higher animals and
single-celled eukaryotes. In microscopic organisms (known
as ciliates) motile cilia are used for locomotion or for
moving fluid over their surface which contributes to the
feeding process.
• In higher animals, such as human beings, motile cilia can
be found in a number of tissues (e.g. respiratory epithelium
and fallopian tubes) where they are either involved in the
clearance of or moving of substances.
• In the respiratory system, cilia trap and remove dirt (as
well as mucous) from the lungs and other parts of this
system. In the fallopian tube, on the other hand, cilia serve
to move the ovum to the uterus.

5. Non-motile Cilia
Primary Cilia are non-motile cilia that were first discovered in 1898. These structures were long believed to be vestigial
organelles. However, recent researches presented the biological roles of primary cilia that they function as a sensory
cellular antenna that coordinates a large number of cellular signalling pathways.
Apart from these, they also help in:
•Proper urine flow by signalling the kidney cells.
•They act as mechanoreceptors or sensory receptors.
•The cilia function by permitting the transfer of important particles from one side of the light-sensitive cells to another in
the retina.
• As compared to motile cilia, primary cilia (9+0) project as single
structures from cell bodies. They are found in virtually all cells in
all mammals. They are primarily involved in sensory functions
and thus allow given body tissues/organs to respond
appropriately.
• Like motile cilia, primary cilia consist of nine doublet
microtubules that make up the axoneme. These microtubules
originate from the basal body that also provides stability.
• Unlike motile cilia, however, primary cilia do not possess dynein
arms and the central singlet microtubules (central pair
microtubules). This is due to the fact that primary cilia are not
motile and thus do not need elements necessary for motility.
Primary cilia play an important role in cell
signaling during development and homeostasis.
Primary cilia (5-10um in length) are exposed to
the extracellular environment, they are
susceptible to various stimuli that contribute to
their role in signaling.
In addition to detecting various chemical factors,
morphogens and growth factors in the
extracellular matrix, primary cilia also detect
changes in pressure and fluid movement across
the cell surface.
Structures that have no apparent function and appear to be residual parts from a past ancestor
are called vestigial structures. Examples of vestigial structures include the human appendix,
the pelvic bone of a snake

6. Cilia Structure
1. Cilia are made up of microtubules coated by the plasma membrane.
2. Motile cilia are characterized by a radial pattern consisting of nine (9)
outer microtubule doublets that surround two singlet microtubules.
Each cilium comprises nine pairs of microtubules that form the outside
ring and two central microtubules.
3. This 9+2 pattern refers to the nine doublet microtubules surrounding
the two microtubules that are centrally located. The ring of microtubule
scaffolding, this structure is called an axoneme.
4. In addition to the microtubules, which are the main components of the
structure, motile cilia are also composed of dynein arms and radial
spokes that contribute to the overall motility of the structure.
5. The axoneme (the bundle of microtubules which measures about
0.25um in diameter) is surrounded by the plasma membrane and the
whole structure (cilia) can be identified under the microscope.
6. The nine outer pairs are made up of motor proteins called dynein.
These are large and flexible that allows the cilia to move.
7. Cilia are attached to the cell at the basal body that is made up of
microtubules arranged in nine triplets.
8. At its base (where it attaches to the cell), the axoneme is attached to
cylindrical structures known as basal bodies measure about 0.4um in
length and 0.2um in width and are made up of the A tubule (nine (9)
triplet microtubules consisting of protofilament microtubules), an
incomplete B tubule as well as an incomplete C tubule.
9. Apart from anchoring cilia in the cytoplasm, basal bodies also play an
important role in the assembly of these structures. Dynein is an ATPase that converts the energy
released by ATP hydrolysis into the mechanical
work of ciliary and flagellar beating

7. Cilia Function
1. The important functions performed by cilia involve
locomotion and sensory functions. They play a major
role in cell cycle and replication and also in the
development of humans and animals.
2. Multiple cilia move in a rhythmic motion that keeps the
internal passageways free from mucus or any foreign
agent. Motile cilia use their rhythmic undulation to
sweep away substances, as in clearing dirt, dust,
micro-organisms and mucus, to prevent disease.
3. A few non-motile cilia act as an antenna that receives
sensory information for the cells and processes these
signals from the surrounding fluids. E.g. the cilia
present in the kidney bend forcefully as the urine
passes. This sends signals to the cells that the urine
is flowing.
4. The non-motile cilia found in the photoreceptors of
retina help in the transport of molecules from one end
to the other.
5. Cilia play roles in the cell cycle as well as animal
development, such as in the heart.
6. Cilia also play a role in cellular communication and
molecular trafficking.

8. Cilia Disorders
Defective cilia functions have been associated with the
following disease and disease syndromes:
• Ciliopathies: It is a genetic disorder of the cilia
structures – the basal bodies or of cilia function.
Dysfunction or defects in primary and motile cilia are
known to cause numerous distressing genetic disorders
known as ciliopathies.
• Primary Ciliary Dyskinesia: It is an autosomal
recessive disorder in which the cilia do not function
normally. This condition prevents the clearing of mucus
from the lungs, ears and sinuses.
• Alstrom syndrome (progressive loss of vision and
hearing, heart disease that enlarges and weakens the
heart muscle, obesity, type 2 diabetes
• Meckel-Gruber syndrome (enlarged kidneys)
• Nephronophthisis (inflammation and scarring (fibrosis)
that impairs kidney function)
• Respiratory infections
• Anosmia (complete loss of smell)
• Male infertility

9. A mechanoreceptor, also called mechanoceptor, is a
sensory receptor that responds to mechanical pressure or
distortion.
Mechanoreceptors detect stimuli such as touch,
pressure, vibration, and sound from the external and
internal environments.

10. Flagella

11. Flagella
• Flagella are the microscopic hair-like structures that are involved
in the locomotion of the cells. The word ‘flagellum’ itself means
‘whip.’
• A flagellum (plural: Flagella) may be described as a filamentous
organelle used for locomotion.
• Like cilia (found in eukaryotic cells), flagella also protrude from
the body of the cell which allows them to perform their functions
effectively.
• However, they are longer in length, measuring between 5 and
20um.
• There are a few organisms in which flagella act as sensory
organs to assist in the change of pH and temperature.
• They are usually found in bacteria, archaea, and eukaryotes.
Cells that possess this structure are referred to as flagellates
and present in both eukaryotic and prokaryotic cells.
• For instance, apart from a majority of bacteria that use flagella
for locomotion, the structure can also be found on such single-
celled organisms as euglena and protozoa species like
Trypanosoma evansi.
• It can be found on gametes of various organisms including
slime molds, fungi, and animals.

12. Flagellum Structure
While flagella can be found in both eukaryotic and prokaryotic cells (and
serve the same purpose) there are various differences with regards to
their structures/composition as well as the mechanism by which they
function between the two types of cells.
The flagella found in prokaryotic cells consist of a globular protein known
as flagellin. Here, the protein wraps around in a helical manner forming a
hollow cylinder along the length of the structure. This protein is absent in
eukaryotic flagellum where it's replaced by protein filaments known as
microtubules.
Some of the differences between the two include:
•Prokaryotic flagella tend to be smaller and less complex compared to
eukaryotic flagella
•Eukaryotic flagella are powered by ATP while those of prokaryotes are
proton-driven
•The prokaryotic flagella are characterized by a rotator movement while
those of eukaryotic cells have bending fashion
•Prokaryotic flagella lack a plasma membrane
Apart from length, the structure and composition of eukaryotic flagella
are similar to cilia found in many eukaryotes

13. Bacterial flagellum is composed of three main parts that include:
1. Basal structure (Rotary motor)
2. Hook (acts as the universal joint)
3. Filament (the helical propeller)
1. Basal body
• In bacteria/prokaryotes, the basal body is a rod that consists of
several rings that are located within the cell membrane. In Gram-
negative bacteria, the rings include the L-ring that is positioned in
the outer membrane of the lipid bilayer and the P ring which is
located in the peptidoglycan layer.
• The basal body is generally divided into several parts that include:
•Protein rings (C ring, MS ring, P ring, and L ring)
•Rod
•Sleeve
Protein rings serve as the proton pumps that are involved in the
movement of hydrogen ions across the membrane. It's this
movement of ions across the membrane that ultimately rotates the
rings and thus the flagellum.
* The basal body, as well as the hook, also serves to anchor the
filament of the structure to the surface of the cell.
The flagella are a helical-like structure that is
composed of flagellin protein.
The flagella structure can be divided into three parts,
namely hook, basal body, and the filament.
• The basal body is attached to the cell membrane and
the cytoplasmic membrane.
• The hook is a broader area that is present at the base
of the filament. It connects the filament to the motor
protein in the base, and the hook length is a gram +ve
bacteria.
• The filament is the hair-like structure that arises from
the hook.

14. Genes encoding different proteins
L-ring -of the bacterial flagellum is the ring in the lipid outer cell membrane
C ring – cytoplasmic ring
MS ring- is a transmembrane protein complex made of FliF and is the base for flagellar structure, assembly and function (Inner membrane)
P ring- It is known to be embedded in the peptidoglycan cell wall.

15. 2. The Hook
• Consisting of 120 subunits of a single protein, the hook
(which is short and curved) acts as the universal joint
that connects the filament to the basal body.
• Unlike the basal body, the hook is not embedded in the
plasma membrane. However, it plays a crucial role in
the motility and taxis of bacteria through the
transmission of motor torque to the filament (propeller)
part of the structure.
• It's composed of 4 main domains that are arranged on
the inside and outside of the structure whose nature
allows for the direct connection between the hook and
the rod.
• The junction between the hook and the filament
consists of two proteins (FlgK and FlgL) which have
been shown to contribute to the formation of the
filament part of the structure.

16. 3. The Filament
• The filament is the elongated part of the flagella. It's tubular
and consists of 11 protofilaments that resemble those found in
the rod and hook parts of the structure.
• The flagellin, which is the main component of the filament,
also consists of four domains that form the inner and outer
part of the structure. The direction to which filament rotates is
dependent on the motor spinning (clockwise or
counterclockwise).
Functions:
• Flagella found in organisms as bacteria, archaea, and various
eukaryotic cells are used for swimming through fluid as well as
swarming
• Flagella have been shown to have sensory functions that
allow cells to detect changes in their environment and respond
effectively (to detect the pH and temperature changes).
• A few eukaryotes also use flagellum to increase reproduction
rates.
• In green algae, studies have suggested that flagella may act
as secretory organelles.
Swarming motility is a rapid and coordinated translocation of a bacterial
population across solid or semi-solid surfaces

17. Types of Flagella:
Organisms may be classified based on the number of
flagella on their surface.
These include:
• Atrichous- with no flagella
•Monotrichous - single flagellum originating from one
end
•Lophotrichous- several flagella at one pole
•Amphitrichous - single flagellum on both poles
•Peritrichous - multiple flagella across the surface of
their bodies
1. Monotrichous is a single flagellum that is present at
one end or the other. These have the ability to rotate
clockwise and anti-clockwise.
2. The lophotrichous are the several flagellums that are
attached at one end or the other. They can rotate
clockwise and anti-clockwise.
3. Peritrichous are the several flagellums that are
attached all over the organism. They are non-polar,
and they can rotate anti-clockwise.
4. Amphitrichous are the single flagellum that is attached
to both the ends of the organism. They are polar and
can rotate clockwise and anti-clockwise.

19. Difference Between Cilia and Flagella
Cilia
•They are present in large numbers.
•They are grouped into the category of protozoans, class Ciliata, in the Ciliated epithelium of the Metazoa and
other classes.
•They form Cirri by fusing into some protozoans.
•It has similar structures and functions as that of flagella, but cilium is shorter, and movement is quite different.
•It exhibits radical motion.
•Its presence is found on the outer surface of some larvae like Mollusca, Annelida, and Nemertines, which
therefore help it with the locomotion.
•Cilia often cover the entire cell.
Flagella
•They are fewer in number.
•Flagella usually do not fuse.
•They are fairly long.
•These are present in protozoans, choanocyte cells of Metazoa, and in other classes- in plants, in gamete cells,
and in algae.
•They are fewer in number.
•It exhibits in coiled motion.
•They are usually found at one end of the cell.

20. Some examples of protozoa are Amoeba, Paramecium,
Euglena and Trypanosoma
Metazoans include insects, worms, jellyfish, octopus,
molluscs, birds, fish, amphibians, reptiles and
mammals, etc.