1. Ethan Blackwood, Anna Menkis, Jeremy Cohen Elenbaas Block 3
Cilia and Flagella
Ethan Blackwood, Anna Menkis, Jeremy Cohen
Elenbaas Block 3

2. Cilia and Flagella: The Basics
Thin tubular structures protruding from membranes of some eukaryotic cells
Aid in movement
Structurally and functionally identical
Cilia
short in size
usually found in great quantities, covering entire cell membrane
Flagella (eukaryotic)
much longer
usually one or two in a cell

3. General Structure Membrane: extensions of cell membrane
Composed of microtubles, organized as following:
Central axoneme with 2 microtubles
Surrounded by 9 microtuble doublets
Axoneme and doublets connected by radial spokes
Dynein molecules bridge gaps between doublets
Figure 1: Interior structure of cilia and flagella (Credit: Florida State University)
Basal body (Kinetosome) located at base
9 sets of 3 microtubules in radial pattern

4. Microtubules Extensions of internal cytoskeleton
Composed of the globular protein tubulin
Doublet: one full microtubule sharing a wall with a smaller, partial microtubule
Basal body: structurally identical to centriole (part of cytoskeleton of an animal cell)

5. Process of Movement Protein dynein is activated by ATP
Dynein arms on one microtubule doublet “grab” an adjacent doublet and “walk” along its length.
Doublets slide past each other and bend
Cilium/flagellum bends
Figure 2: Movement of cilia and flagella (Credit: Benjamin/Cummings)

6. General Functions
In protista: movement of organism through environment
Same function applies to motile (flagellated) sperm cells
In multicellular eukaryota: transport extracellular substances (e.g. water, food)

7. Where Found Cilia Protista (e.g. paramecium)
Human respiratory tract, keeping dust and debris out of lungs
Digestive systems (e.g. of snails)
Flagella (eukaryotic)
Protista (e.g. euglena)
Motile (flagellated) sperm cells of animals and some plants
(Bacterial and archaeal flagella exist in some prokaryotes)

8. Ciliopathy Problems Primary ciliary dyskinesia
Recessive genetic disorder
Defective cilia lining respiratory tract and fallopian tube
Susceptibility to chronic, recurring respiratory infections
Polycystic kidney disease
Defective cilia in the renal tube cells (kidney)
Cysts, enlargement of kidneys, possible damage to other organs
Bardet-Biedl syndrome
Problem in basal body caused by genetically mutated cilia
Numerous consequences, ranging from obesity to mental retardation
Ectopic pregnancy
Fallopian cilia fail to move fertilized ovum to uterus

9. Two Theories of Evolution
Endosymbiotic model
Proposed by Lynn Margulis
Cilia and flagella are results of symbiosis between ancient eukaryotic and prokaryotic cells
Supporting evidence (weaker)
Mitochondria and chloroplasts as endosymbiotic examples
Some eukaryotes symbiotically use bacteria as motility organelles
Endogenous model
Cilia and flagella developed from existing eukaryotic cytoskeleton
Supporting evidence (stronger)
Both cilia/flagella and cytoskeleton contain dynein and tubulin
All eukaryotic kingdoms contain motile, 9+2 flagella, suggesting that the common eukaryotic ancestor had this trait

10. Works Cited
Campbell, Neil A. et al. Biology: Concepts & Connections. San Francisco: Benjamin/Cummings, 2000.
“Cilium-related disease.” Cilium. New World Encyclopedia. newworldencyclopedia.org/entry/Cilia
Davidson, Michael W. “Cilia and Flagella.” Molecular Expressions: Exploring the World of Optics and Microscopy. micro.magnet.fsu.edu/cells/ciliaandflagella/ciliaandflagella.html
“How important is endosymbiosis?” Understanding Evolution. University of California Museum of Paleontology and National Center for Science Education. evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_06
Kaiser, Gary E. “Composition and Functions of Eukaryotic Cellular Structures: Cilia and Flagella.” The Eukaryotic Cell. Community College of Baltimore County. student.ccbcmd.edu/courses/bio141/lecguide/unit3/eustruct/ciliaflag.html
(For further reading) Mitchell, David R. The Evolution of Eukaryotic Cilia and Flagella as Motile and Sensory Organelles SUNY Upstate Medical University. upstate.edu/cdb/mitcheld/publications/Jekey_Mitchell.pdf