Cilia and Flagella
Structure and Function in
Eukaryotes
By Justin Robbins and Katrina Truebenbach
Overview
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Cilia and Flagella are
organelles that are
primarily used for the
transportation of the cell.
They propel the cell by
flicking back and forth.
Cilia are short and
reminiscent of hairs.
There are many per cell.
Flagella are longer and
there are far fewer per
cell. They are reminiscent
of a tail.
Real-life Examples:
Eukaryotes
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Most common in single-celled organisms
(protists).
However, some multi-cellular organisms have
cilia and flagella.
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Human windpipe cells and some lung cells have cilia
to clean the respiratory system of breathing hazards.
Fish have cilia to help bring water through the gills.
Many types of sperm have flagella to help them
move.
Structure: 9+2 Pattern
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Cilia or flagella is composed of
microtubules that are encased in a
plasma membrane. This bundle of
microtubules is called the axoneme.
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A plasma membrane is made of lipids
and proteins and is essentially the same
as a normal cell membrane.
There are 9 pairs of connected
microtubules in a circle towards the
outside edge of the cilia/flagella. These
are called the outer microtubule
doublets.
The outer microtubules are connected
to each other in a ring with cross-links
(not pictured).
The outer microtubules also connect to
the center structure with radial spokes.
These outer microtubules surround
another pair of central microtubules,
which are not connected.
Structure: Basal Body
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The 9+2 pattern
continues throughout the
entire organelle until the
base.
The base is called the
Basal Body. It is the
foundation of the cilia or
flagella and is embedded
in the cell membrane.
It does not have a pair of
central microtubules.
Instead, it has nine
triplets of microtubules.
How They Work: Dynein Arms
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Each of the outer microtubule pairs
have a set of dynein, a functional
protein, arms.
These arms change shape and
subsequently create a sliding force,
therefore moving the tubule pairs.
Since the pairs are held together
with cross-links and are anchored in
the cell membrane, the
microtubules bend as a result of
this force.
If they were not held together, the
force exerted would cause the two
doublets to slip past each other.
This bending motion makes the cilia
or flagella to flick back and forth,
therefore propelling the cell
forwards.
How They Work: ATP
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The change of shape
of the dynein arms is
powered by ATP.
ATP, or Adenine-TriPhosphate, is
molecule that most
cells use as their main
energy source.
Differences in Motion:
single-celled organisms
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Cilia movement is well timed with each
other and propel the organism in a wavelike motion.
Flagella in eukaryotes give the organism
smoother movement.
Flagella in prokaryotes rotate, like a motor.
Primary Cilia
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Primary Cilium are an alternate type of cilia.
They do not aid in motion and are therefore
referred to as immotile cilia.
Primary cilia do not have central microtubules.
They have a 9+0 structure.
They have sensory functions.
 Examples: monitoring flow in the kidneys and
detecting smells.
 Defects in kidney primary cilia can lead to
kidney disease.
Sources
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Campbell, Mitchell, and Reece. "Cilia and Flagella Move When Microtubules Bend."
Biology: Concepts and Connections. 3rd ed. Reading, Massachusetts:
Benjamin/Cummings, 2000. 65. Print.
Campbell, Mitchell, and Reece. "Glossary." Biology: Concepts and Connections. 3rd
ed. Reading, Massachusetts: Benjamin/Cummings, 2000. G-18. Print.
Cilia and Flagella. Photograph. University of Illinois. Web. 21 Nov. 2010.
<http://www.uic.edu/classes/bios/bios100/lectf03am/cilia_flagella.jpg>.
Davidson, Michael W. "Cilia and Flagella." Molecular Expressions. Florida State
University, 13 Dec. 2004. Web. 21 Nov. 2010.
<http://micro.magnet.fsu.edu/cells/ciliaandflagella/ciliaandflagella.html>.
Diagrams of Cilia and Flagella. Digital image. Both Brains and Beauty. Web.
<http://www.bothbrainsandbeauty.com/academic-discussions/cilia-vs-flagella461>.
Diagrams of Dynein Arms. Digital image. University of Illinois. Web. 21 Nov. 2010.
<http://www.uic.edu/classes/bios/bios100/lectures/07_35_flagellas_bendL.jpg>.
Kimball, John W. "Cilia and Flagella." Kimball's Biology Pages. 28 July 2007. Web. 21
Jan. 2010.
<http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Cilia.html>.