Cytoskeleton 1.docx

Cytoskeleton- a intricate network of protein filaments that extends throughout the cytoplasm. Structure and composition of the cytoskeleton Cytoskeletal proteins forms polymers/fibres from small protein subunits held by noncovalent bonds. Made up of 3 types of protein filaments. Intermediate fila...

Cytoskeleton- a intricate network of protein filaments that extends throughout the cytoplasm. Structure and composition of the cytoskeleton Cytoskeletal proteins forms polymers/fibres from small protein subunits held by noncovalent bonds. Made up of 3 types of protein filaments. Intermediate filaments Microtubules- alpha and beta-tubulin Microfilaments: F-actin and G-actin Intermediate filaments Main function is to withstand the mechanical stress when a cell is stretched. Toughest and most durable cytoskeletal filaments Rope like structures Extends across the cell cytoplasm. Microtubules Long, stiff, and hollow protein tubes that can rapidly disassemble in one location and assemble in another. Grows out from small structures near centre of the cell called centrosome. Mainly responsible for transporting and positioning membrane organelles. Guides intracellular transport of various cytosolic macromolecules. Can also form cilia and flagella. Microtubules are built from molecules of tubulin- each which is a dimer composed of similar globular proteins called alpha and beta tubulin which are tightly bound via noncovalent bonds. Tubulin dimers stack together to form the wall of hollow microtubule. Microfilaments Actin filaments interact with large number of actin binding proteins. Can form stuff structures e.g., microvilli. Localised at the cell cortex. Support of plasma membrane Actin filaments are thin and flexible and shorter than microtubules but many more of them. Found in cross-linked bundles and networks. G-subunit polymerises to form actin filament. The role of cytoskeleton in organisation of cells Functions of cytoskeleton Cell movement and mobility Maintenance of cell shape and polarity Intracellular transport of organelles and vesicles Dynamic- responsive to extracellular and intracellular signals Summary