Cellular and flagellar movement is carried out by all of the following except
Intermediate filament is 8 to 14 nm in diameter and is made up of various subunits. Some of these filaments connect the nuclear membrane to the cell membrane. They form a flexible scaffolding for the cell and help it resist external pressure. In their absence, cells rupture more easily, and when they are abnormal in humans, blistering of the skin is common. The proteins that make up intermediate filaments are cell type specific and are thus frequently used as cellular markers. For example, vimentin is a major intermediate filament in fibroblasts, whereas cytokeratin is expressed in epithelial cells. Microfilaments are long solid fibers with a 4 to 6 nm diameter that is made up of actin. Although actin is most often associated with muscle contraction, it is present in all types of cells. It is the most abundant protein in mammalian cells, sometimes accounting for as much as 15% of the total protein in the cell. Its structure is highly conserved; for example, 88% of the amino acid sequences in yeast and rabbit actin are identical. Actin filaments polymerize and depolymerize in vivo, and it is not uncommon to find polymerization occurring at one end of the filament while depolymerization is occurring at the other end. Filamentous (F) actin refers to intact microfilaments and globular (G) actin refers to the unpolymerized protein actin subunits. F-actin fibers attach to various pas of the cytoskeleton and can interact directly or indirectly with membrane-bound proteins. They reach to the tips of the microvilli on the epithelial cells of the intestinal mucosa. They are also abundant in the lamellipodia that cells put out when they crawl along surfaces. The actin filaments interact with integrin receptors and form focal adhesion complexes, which serve as points of traction with the surface over which the cell pulls itself. In addition, some molecular motors use microfilaments as tracks. Microtubules are long, hollow structures with 5-nm walls surrounding a cavity 15 nm in diameter. They are made up of two globular protein subunits: a-and b-tubulin. A third subunit,g-tubulin, is associated with the production of microtubules by the centrosomes. The a and b subunits form heterodimers, which aggregate to form long tubes made up of stacked rings, with each ring usually containing 13 subunits. Because of their constant assembly and disassembly, microtubules are a dynamic poion of the cell skeleton. They provide the tracks along which several different molecular motors move transpo vesicles, organelles such as secretory granules, and mitochondria, from one pa of the cell to another. They also form the spindle, which moves the chromosomes in mitosis. Cargo can be transpoed in either direction on microtubules. REF: GANONG'S REVIEW OF MEDICAL PHYSIOLOGY KIM BARRETT, SCOTT BOITANO, HEDDWEN BROOKS, SUSAN BARMAN TWENTY THIRD EDITION PAGE NO:35,36
Intermediate filaments
Actin
Tubulin
Myosin
General physiology