Episode 13 - Flagellum, Cillium, and Cell Movement
Flagella and cilia in Eukaryotic cells are membrane-bound organelles composed of a core ring of nine pairs (doublets) of microtubules around a central pair of microtubules, called an axoneme. Special motor proteins called dyenin connect each of the nine microtubule doublets on the outer ring, and are responsible for the beating of cilia and flagella. Flagella and cilia are anchored beneath the plasma membrane to a microtubule organizing center, such as a centriole (basal body). Prokaryotic Flagella do not contain microtubules.
Eukaryotic centriole diagram. (Source: Wikimedia commons)
Flagellum
- movement around environment
- motor proteins (like dyenin) to make the flagellum beat in a rhythmic motion, which propels the cell forward
- Flagella are mainly found on free-living cells like sperm.
Escherichia coli cells use long, thin structures called flagella to propel themselves. These flagella form bundles that rotate counter-clockwise, creating a torque that causes the bacterium to rotate clockwise. (Source: Wikimedia Commons)
Cilium
- Serves the same function as the flagellum: cell mobility.
- Cilia beat with a back and forth motion, as opposed to a propeller-like motion of flagella
- Cilia are shorter and occur in far greater numbers than flagella.
- There can be multiple cilia on one cell, but generally only 1 flagellum on one cell.
- Cilia are generally found in multicellular organisms (as ciliated tissues)
- Cilia in multicellular organisms also function to stir their surroundings, like epithelial tissues in a human’s respiratory tract, which beats cilia to carry debris-filled mucus out of the lungs.
Cross-section micrograph of axoneme ("9+2" structure is visible). (Source: Wikimedia Commons)
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