Flagella and Cilia
A. P. Biology
Chapter 6
Mr. Knowles
Liberty Senior High School
Flagella of Prokaryotes
(Bacteria)
• Composed of a flagellin
subunit.
• Usually sheathed (covered).
• Rotates by way of a basal
body in the bacterial cell.
• Unique to bacteria.
Show me bacterial flagella in
action!
Eukaryotic Flagella
• Completely different than bacteria.
• Circle of 9 fused pairs of
microtubules that make a cyclinder.
• 2 unfused microtubules in the
center of cylinder.
• Called the 9 + 2 structure.
EM X-Section of Human Sperm
Eukaryotic Flagella
• Whip-like appendage, used
in movement and longer
than cilia.
• Is an outward projection of
cytoplasm.
Flagella beating pattern
Direction of swimming
(a) Motion of flagella. A flagellum
usually undulates, its snakelike
motion driving a cell in the same
direction as the axis of the
flagellum. Propulsion of a human
sperm cell is an example of
flagellatelocomotion (LM).
Figure 6.23 A
1 µm
Eukaryotic Flagellum in Action!
Eukaryotic Cytoskeleton and
Cell Movements
Cilia
• More numerous than
flagella.
• Cilia of unicellular
eukaryotes = movement
of cell. Ex. Paramecium
Ciliary Motion
(b) Motion of cilia. Cilia have a backand-forth motion that moves the
cell in a direction perpendicular
to the axis of the cilium. A dense
nap of cilia, beating at a rate of
about 40 to 60 strokes a second,
covers this Colpidium, a
freshwater protozoan (SEM).
15 µm
Figure 6.23 B
Cilia
• Cilia of multicellular eukaryotes
= movement of debris, sensory
cells of vertebrate ear, epithelia of
respiratory and reproductive
tracts.
• Have similar microtubule
structure of 9 + 2 as eukaryotic
flagella.
Cilia of Paramecium caudatum
Show me ciliated epithelium!
Cilia and flagella share a common
ultrastructure
Outer microtubule
doublet
Dynein arms
0.1 µm
Central
microtubule
Outer doublets
cross-linking
proteins inside
Microtubules
Radial
spoke
Plasma
membrane
Basal body
(b)
0.5 µm
(a)
0.1 µm
Triplet
(c)
Figure 6.24 A-C
Cross section of basal body
Plasma
membrane
E M of the Cross-section of a
Sperm Tail
How Do Cilia Move?
Protein Dynein:
–Is responsible for the bending
movement of cilia and flagella
Microtubule
doublets
ATP
Dynein arm
(a)
Figure 6.25 A
Powered by ATP, the dynein arms of one microtubule doublet
grip the adjacent doublet, push it up, release, and then grip again.
If the two microtubule doublets were not attached, they would slide
relative to each other.
ATP
Outer doublets
cross-linking
proteins
Anchorage
in cell
(b) In a cilium or flagellum, two adjacent doublets cannot slide far because
they are physically restrained by proteins, so they bend. (Only two of
Figure 6.25 B the nine outer doublets in Figure 6.24b are shown here.)
1
3
2
(c)
Localized, synchronized activation of many dynein arms probably
causes a bend to begin at the base of the Cilium or flagellum and
move outward toward the tip. Many successive bends, such as the
ones shown here to the left and right, result in a wavelike motion. In
this diagram, the two central microtubules and the cross-linking
proteins are not shown.
Figure 6.25 C
– Are found in
microvilli
Microvillus
Plasma membrane
Actin
Filaments
Intermediate filaments
Figure 6.26
0.25 µm
E. M. of Cross-section of Sperm
Tail with Defective Dynein
What is Duchenne’s Muscular
Dystrophy ?