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TOPIC 10 - motor proteins is ciliary dynein which looks and...

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TOPIC 10: CILIA AND FLAGELLA Cilia and flagella contain stable microtubules called axonemal microtubules. The stable MTs of cilia and flagella are moved by motor proteins called ciliary dynein. Cilia and flagella can be used to propel a cell through its medium or move the medium over the cell. Cilia (singular, cilium) are thin hair-like structures which extend from the surface of many eukaryotic cells and are covered by plasma membrane . Each cilium has a core of stable microtubules which grow from a basal body and there may be billions of cilia on a cm 2 of epithelium. Flagella (singular, flagellum) are like cilia in basic design but are usually very much longer and less numerous. The internal structure is similar in cilia and flagella being associated with what is called the "9 + 2" array of microtubules . These microtubules are associated with numerous accessory proteins which bundle the microtubules and function as motor proteins. The most important of these
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Unformatted text preview: motor proteins is ciliary dynein which looks and functions much like the cytoplasmic dynein we have already seen. The subunit of microtubules is a tubulin heterodimer called αβ-tubulin . Each α or β monomer has a binding site for one molecule of the nucleotide GTP. The GTP that binds to an α-tubulin monomer is trapped at the dimer interface and thus does not thereafter exchange nor is it hydrolyzed to GDP. The GTP that binds to a β-monomer is exposed and thus can be hydrolyzed or exchanged and thus can be either GDP or GTP. The significance of this is that a dimer with two molecules of GTP is more stable than a dimer with only one GTP. The most recently assembled portion of the microtubule with the greatest proportion of GTP is the most stable and thus will grow more readily than the older part. This is what makes the end furthest from the MTOC the plus end....
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