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

(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).

1 µm

Direction of swimming

Figure 6.23 A

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 back- and-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).

Figure 6.23 B

15 µm

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

(a)

(c)

(b)

Outer microtubuledoublet

Dynein arms

Centralmicrotubule

Outer doublets cross-linkingproteins inside

Radialspoke

Plasmamembrane

Microtubules

Plasmamembrane

Basal body

0.5 µm

0.1 µm

0.1 µm

Cross section of basal body

Triplet

Figure 6.24 A-C

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

Microtubuledoublets ATP

Dynein arm

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.

(a)

Figure 6.25 A

Outer doubletscross-linkingproteins

Anchoragein cell

ATP

In a cilium or flagellum, two adjacent doublets cannot slide far because they are physically restrained by proteins, so they bend. (Only two ofthe nine outer doublets in Figure 6.24b are shown here.)

(b)

Figure 6.25 B

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.

(c)

1 3

2

Figure 6.25 C

– Are found in microvilli

0.25 µm

Microvillus

Plasma membrane

ActinFilaments

Intermediate filaments

Figure 6.26

http://www.stolaf.edu/people/giannini/flashanimat/cellstructures/micro%20slide.swf

E. M. of Cross-section of Sperm Tail with Defective

Dynein

What is Duchenne’s Muscular Dystrophy ?