311C_F10_chapter 6 p3 - Cytoskeleton and extracellular...

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Unformatted text preview: Cytoskeleton and extracellular components Chapter 6 The cytoskeleton Is a network of fibers extending throughout the cytoplasm Figure 6.20 Microtubule 0.25 m Microfilaments Table 6-1b Actin subunit 10 m 7 nm Table 6-1a 10 m Column of tubulin dimers Tubulin dimer 25 nm Table 6-1c 5 m Keratin proteins Fibrous subunit (keratins coiled together) 812 nm Microfilaments (Actin Filaments) The structural role of microfilaments is to bear tension, resisting pulling forces within the cell They form a 3-D network called the cortex just inside the plasma membrane to help support the cells shape Types of movement mediated by Microfilaments Muscle contraction Cytoplasmic streaming Amoeboid movement Microfilaments that function in cellular motility contain the protein myosin in addition to actin In muscle cells, thousands of actin filaments are arranged parallel to one another Thicker filaments composed of myosin interdigitate with the thinner actin fibers Microfilaments that function in cellular motility Contain the protein myosin in addition to actin Actin filament Myosin filament Myosin motors in muscle cell contraction. (a) Muscle cell Myosin arm Figure 6.27 A http://www.sciencemag.org/feature/data/1049155s1.mov Amoeboid movement localized contraction of actin and myosin filaments Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Figure 6.27 B http://www.middlesexcc.edu/faculty/Barbara_Bogner/112unittwo.html Cytoplasmic streaming Is another form of locomotion created by microfilaments Nonmoving cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Parallel actin filaments Cell wall (b) Cytoplasmic streaming in plant cells Figure 6.27 C http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation_-_cytoplasmic_streaming.html Microfilaments: Cell Division Microtubules Hollow rods about 25 nm in diameter and about 200 nm to 25 microns long Functions of microtubules: Shaping the cell Guiding movement of organelles Separating chromosomes during cell division Cellular Monorails Microtubles are small hollow cylinders made of the globular protein tubulin....
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311C_F10_chapter 6 p3 - Cytoskeleton and extracellular...

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