What is the relationship between microtubules and cilia and flagella?  

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The cytoskeleton of a cell is made up of three types of fibers. These are the microtubules, microfilaments and intermediate filaments. Microtubules (actin filaments) are the thickest of all of these fibers while microfilaments are the thinnest.

One function of microtubules involves cell motility or movement as seen in the flagella and cilia in various cell types. Microtubules may extend from some cell types as a flagella which looks like a long tail or cilia which are smaller hairs that extend out from the plasma membrane. They differ in their beating patterns to achieve movement. Flagella seem to undulate while cilia have a power stroke and then a recovery stroke. The flagellum in a single sperm cell undulates and propels the sperm forward. The many tiny cilia surrounding a Paramecium beat in rhythm and cause the organism to move through its watery environment.

Both cilia and flagella have a core consisting of microtubules surrounded by the plasma membrane. To serve as an anchor, there is a structure called a basal body. To bend the cilia or flagella during movement, a motor protein called dynein is essential. The dynein arms grab, move and release outer microtubules causing the microtubules to curve which causes  cilia or flagella to bend resulting in motion.

There is a typical pattern for the arrangement of microtubules within a cilia or flagella. I have included a link with a picture of their arrangement. It is a "9 +2" arrangement of 2 microtubules in the center with 9 pairs of microtubules arranged in a circle around them.  To summarize, microtubules and their associated motor proteins along with ATP allow locomotion to occur in certain cell types that have cilia or flagella.



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