27Jan_8 - Biological Science I Tuesdays and Thursdays...

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Biological Science I Tuesdays and Thursdays 8:00-9:15, HCB 102 Mondays 5:15-6:15, KIN 1024 27 January 2011 – Lecture 8 CYTOSKELETON 1. The cytoskeleton is a network of fibers extending throughout the cytoplasm 2. It organizes the cell’s structures and activities, anchoring many organelles 3. It is composed of three types of molecular structures: a. Microtubules - Slide a.i. the thickest of the three components of the cytoskeleton a.ii. hollow rods about 25 nm in diameter and about 200 nm to 25 microns long a.iii. Functions of microtubules: a.iii.1. Shaping the cell a.iii.2. Guiding movement of organelles a.iii.3. Separating chromosomes during cell division a.iv. Centrosomes and Centrioles a.iv.1. In many cells, microtubules grow out from a centrosome near the nucleus a.iv.2. The centrosome is a “microtubule-organizing center” a.iv.3. In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring – slide a.v. Cilia and Flagella a.v.1. Microtubules control the beating of cilia and flagella, locomotor appendages of some cells a.v.2. Cilia and flagella differ in their beating patterns a.v.3. Cilia and flagella share a common ultrastructure: a.v.3.a. A core of microtubules sheathed by the plasma membrane a.v.3.b. A basal body that anchors the cilium or flagellum a.v.3.c. A motor protein called dynein, which drives the bending movements of a cilium or flagellum a.v.4. Dynein “walking” moves flagella and cilia: a.v.4.a. Dynein arms alternately grab, move, and release the outer microtubules a.v.4.b. Protein cross-links limit sliding a.v.4.c. Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum b. Microfilaments, b.i. also called actin filaments b.ii. the thinnest components b.iii. Solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits b.iv. The structural role of microfilaments is to bear tension, resisting pulling forces within the cell b.v. They form a 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape b.vi. Bundles of microfilaments make up the core of microvilli of intestinal cells 1
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Biological Science I Tuesdays and Thursdays 8:00-9:15, HCB 102 Mondays 5:15-6:15, KIN 1024 27 January 2011 – Lecture 8 b.vii. Microfilaments that function in cellular motility contain the protein myosin in addition to actin b.vii.1. In muscle cells, b.vii.1.a. thousands of actin filaments are arranged parallel to one another b.vii.1.b. Thicker filaments composed of myosin interdigitate with the thinner actin fibers b.vii.2. In Amebiod movement b.vii.2.a. Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments b.vii.3. Cytoplasmic streaming b.vii.3.a. circular flow of cytoplasm within cells b.vii.3.b. This streaming speeds distribution of materials within the cell b.vii.3.c. In plant cells, actin-myosin interactions and sol-gel transformations
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27Jan_8 - Biological Science I Tuesdays and Thursdays...

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