Cilia/ Flagella

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  1. What are cilia/ flagella?
    • Cilia and Flagella
    • Hairlike, motile organelles that project from the surface of a variety of eukaryotic cells that emerge from a basal body
  2. movement of cilia
    • likened to an oar as it moves the cell in a direction perpendicular to the cilium
    • -          in its power stroke, the cilium is maintained in a rigid state as it pushes against the surrounding medium
    • -          in its recovery stroke, the cilium becomes flexible, offering little resistance to the medium
  3. Number of cilia
    large numbers on the cell's surface
  4. Funciton of cilia
    move fluid and particulate material through various tracts; some are nonmotile and have a sensory function
  5. Movement of flagella
    Movement: exhibit a variety of different beating patterns (waveforms) depending on cell time
  6. Number of flagella
    single or pairs
  7. function of flagella
  8. Internal structure
    - covering
    - core
    • -          covered by membrane that is continuous with the plasma membrane
    • -          core, called the axoneme, contains an array of microtubules that runs longitudinally through the entire organelle
  9. Explain the axoneme in terms of...
    - microtubules
    - ends
    - central
    • o   consists of nine peripheral doublet microtubules surrounding a central pair of single microtubules (9+2 array)
    • o   plus ends are at the tip of the projection and the minus ends are at the base
    • o   one complete microtubule and one incomplete microtubule (usually has 10 or 11 subunits)
    • o   central tubules enclosed by central sheath, which isconnected to the A tubules of the peripheral doublets by a set of radial spokes
  10. Explain the axoneme in terms of...
    - doublets
    - arms
    - A and B
    • o   the doublets are connected to one another by an interdoublet bridge composed of the protein, nexin
    • o   arms (inner and outer) are present on the A tubule
    • A and B tubules of the basal body elongate to form the doublets of the cilium or flagellum
  11. Mechanism of locomotion
    - in the intact axoneme
    -          In the intact axoneme, the stem of each dynein molecule (with its light and intermediate chains) is tightly anchored to the outer surface of the A tubule, with the globular heads and stalks projecting toward the B tubule of the neighboring doublet
  12. Mechanism of locomotion
    - Steps
    • o   the dynein arms anchored along the A tubule of the lower double attach to binding sites on the B tubule of the upper doublet
    • o   the dynein molecules undergo a conformational change, or power stroke, that causes the lower doublet to slide toward the basal end of the upper doublet
    • o   the dynein arms have detached from the B tubule of the upper doublet
  13. Resistance

    • -          Resistance to sliding provided by the nexin bridges causes the axoneme to bend in response to the sliding force
    • o   sliding on one side of the axoneme alternates with sliding on the other side so that a part of the cilium or flagellum bends first in one direction and then in the opposite direction
    • this requires that the dynein arms on one side are active, while those on the other are inactive
Card Set:
Cilia/ Flagella
2013-12-10 03:48:31
Biology Final

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