... stronger than most cells because of their protective function: this is because their cytoskeleton is much more extensive and has a greater proportion of certain strengthening proteins. The cytoskeleton is not homogeneous, but has several components. As I have just mentioned, there are many different functions of the cytoskeleton and these functions can usually be associated with a certain component. Microtubules are the most prominent parts of the network. They are about 24nm (240 A?) in diameter and are composed of the protein tubulin, built up from globular tubulin monomers. These subunits are arranged in a cylindrical tube in which the subunits are stacked up in a large spiral to make the tube shape. In fact, there are two subunits, ?-tubulin and ?-tubulin, which bind together to give a heterodimer. Microfilaments are usually 1nm (100 A?) in diameter and consist of the protein actin. These cover the whole of the ...

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