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Unformatted text preview: -1-LECTURE 294 November 2009 (P. J. Hollenbeck) BIOL231The Cytoskeleton: Filaments and Their Building Blocks Read: Chap 17: 571-79; 592-96 (all of Chap. 17 over next 5 lectures) Be sure to study DVD animation 17.1; problem = exam III 06, #7I. The eucaryotic cell has an endoskeleton(A) Cell structure(1) So far in this course we have looked at the membrane boundaries in the cell, and atthe proteins and organelles that occupy the cytoplasm. But none of these structures iscapable of conferring on the cell its mechanical properties. What allows a cell to hold aparticular shape, or change shape? What organizes the components of the cytoplasm for instance, what allows organelles to stay in one place, or to move from one place toanother. And what allows the entire cell to move? (2) A framework of protein filaments, called the CYTOSKELETON underlies all ofthese properties. It provides structural support for the cell, resists tension anddeformation, provides a docking site for many proteins and organelles, serves as thetracks for organelle movement, and generates force to change the shape of the cell, or toallow it to locomote. (B) Three filament systems(1) The cytoskeleton is composed ofthree distinct filament systems, each withdifferent building blocks and differentproperties. These are the intermediatefilaments, themicrotubules, and theactin filaments. Most vertebrate cellscontain all three systems. There are afew other filament systems in certaincells, but we will not discuss them here. (2) As shown in the figure at left (andsee panel 17-1 in ECB), the threefilament systems are arranged differentlywithin a typical cell (here, an epithelialcell). The filaments are easilydistinguished from each other in theelectron microscope: actin filaments arethe thinnest, with a diameter of approx 7nm; intermediate filaments are 10 nm indiameter, and microtubules are 25 nm indiameter, with a characteristic helicalpattern of subunits apparent in their wall. All 3 filaments are formed by non-covalent associationof subunit proteins.-2-II. Physical properties of cytoskeletal filaments(A) Intermediate filaments (figs 17-2, -3,- 4)<they are so named for historical reasons: they were discovered in muscle cells, and their diameter liesin between that of muscle actin, or thin filaments, and muscle myosin, or thick filaments>(1) Of the 3 filament systems in the cell, intermediate filaments (or IFs) are the mostresistant to disruption. In fact, if you use harsh conditions such as heat, detergent, andhigh salt to destroy virtually everything else in the cell, the network of IFs remainsalmost undisturbed. (2) Of the 3 filament systems in the cell, the IFs also have the greatest tensile strength....
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This note was uploaded on 12/18/2009 for the course BIOL 101 taught by Professor Wormer during the Fall '08 term at Purdue University-West Lafayette.
- Fall '08