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Cilia and Flagella

Ethan Blackwood, Anna Menkis, Jeremy Cohen Elenbaas Block 3. Cilia and Flagella. Cilia and Flagella: The Basics. Thin tubular structures protruding from membranes of some eukaryotic cells A id in movement Structurally and functionally identical Cilia short in size

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Cilia and Flagella

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

  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 microtubledoublets • Axoneme and doublets connected by radial spokes • Dyneinmolecules 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. Figure 2: Movement of cilia and flagella (Credit: Benjamin/Cummings) 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

  6. General Functions • Inprotista: movement of organism through environment • Same function applies to motile (flagellated) sperm cells • Inmulticellulareukaryota: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 ciliarydyskinesia • 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.” 2004. 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. 2006.SUNY Upstate Medical University. upstate.edu/cdb/mitcheld/publications/Jekey_Mitchell.pdf

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