ethan blackwood anna menkis jeremy cohen elenbaas block 3 n.
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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 the basics
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
general structure
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
microtubules
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)
process of movement

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
general functions
General Functions
  • Inprotista: movement of organism through environment
    • Same function applies to motile (flagellated) sperm cells
  • Inmulticellulareukaryota:transport extracellular substances(e.g. water, food)
where found
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)

ciliopathy problems
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
two theories of evolution
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
works cited
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