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Note Feb 4, 2013 recitation and lecture

Intermediate filaments are important for tensile

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INTERMEDIATE FILAMENTS are important for tensile strength. They resist stretching and allow cells to be connected to each other and the substrate. The nuclear envelope is lined with an intermediate filament network known as the nuclear lamina . In epithelia, IFs are linked to IFs in adjacent cells and to components of the extracellular matrix. These linkages help anchor the cells to each other and to the substratum. IFs are critical for the integrity of epithelial tissues, as seen in the case of many human genetic blistering diseases (e.g., epidermolysis bullosa simplex). These diseases can be caused by mutations in cytokeratins. Nuclear lamina; Fig. 20.16 MCB 6e
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Cell Biology (020.306) CYTOSKELETON Weeks 2 and 3 8 MICROTUBULE-BASED MOTORS Two major families: kinesins and dyneins. Kinesins are classified into three subtypes depending on the location of their motor domain (the site for ATP and microtubule-binding domain). Kin-N and Kin-C motors have their motors at the N and C termini; Kin-M motors have theirs in the middle. Kin-N motors are plus-end directed. Kin-C motors and dyneins are minus- end directed. Kin-N motors and dyneins drive the intracellular movement of membrane-bound organelles. Organelle movement occurs in all cells, but it is taken to the extreme in neurons where it is called fast axonal transport. Several microtubule based motors contribute to the movements of chromosomes and microtubules that are seen in mitosis. CELL LOCOMOTION Cells locomote in two basic ways: swimming and crawling. The same movements that allow single celled creatures to swim can be used to propel fluid past a cell that is immobilized in a tissue. Cell swimming is powered by cilia and flagella, which contain a core microtubule structure called the axoneme. Axonemes are specialized arrays of 9 + 2 microtubules (outer doublets surrounding a central pair) that emanate from basal bodies (identical in structure to centrioles). The outer doublet microtubules are densely decorated with axonemal dyneins that provide the force for axoneme bending. Outer arm dyneins provide the power for axoneme bending whereas inner arm dyneins fine tune the movement. To create a bend and to allow the complicated whiplike and power stroke/recovery stroke beat patterns seen for flagella and cilia, some dyneins must be active while others are not. Cell crawling depends on actin dynamics. Cells can move by extending pseudopodia, lamellapodia or filopodia. The actin in these structures can be organized into parallel bundles, crosslinked gels or branched networks. Localized actin
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Cell Biology (020.306) CYTOSKELETON Weeks 2 and 3 9 assembly can provide enough force to cause the entire cell membrane to be pushed outward. Motors of the myosin family can also participate in cell locomotion, by propelling actin filaments
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INTERMEDIATE FILAMENTS are important for tensile strength...

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