Bio Chem 12

Lecture 12 Compare and contrast the FUNCTION of actin filaments, intermediate filaments, and microtubules in the cytoskeleton

Compare and contrast the STRUCTURE

List the SUBUNITS of the three classes of cytoskeleton filaments and describe their ASSEMBLY

List the MOTOR PROTEINS associated

See appendix for great table. Actin: cortical cytoskeleton; cellular movement; stress fibers; microvilli; ms. Contraction; cytokinesis in cell division Intermediate: mechanical strength (NOT dynamic like other two) Microtubule: Organelle movement – axonal transport in neurons, intracellular transport via vesicles, cilia and flagella; Chromosome segregation during cell division ♦All three consist of monomers that assemble via non-covalent interactions into polymers ♦Actin and Microtubules: both contain binding proteins with a nucleate filament formation at the + end and a capping protein at the – end to prevent disassembly ♦Actin: 2 stranded helix; 7nm diameter; regulated by ATP; most dynamic ♦Intermediate filaments: Variety of Rod shaped, fibrous proteins with head, rod, and tail domains; 10nm diameter; Stable, no movement. (keratins, vimentin, neurofilaments, nuclear lamins) ♦Microtubules: 25nm; rigid, hollow tubes; dynamic; regulated by GTP Microfilaments: Actin subunits = double stranded helix. G-actin (globular) polymerizes into f-actin (filamentous). ATP regulated addition of monomer to the + end, - end anchors. Intermediate filaments: subunits of fibrous proteins with head, rod, and tail domains. Dimers are formed via coiled-coil interactions of the rod domains. They group into rope-like staggered filaments. Anchored by desmosomes and hemidesmosomes. Microtubules: Tubulin (globular proteins) α and β filament monomers with γ nucleate filament; Addition of subunits to + end. Anchored in centrosome or basal body. Growth Regulated by GTP binding and hydolysis . Actin Motor Proteins: Myosin

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with microtubules and actin filaments

List the cellular LOCATIONS of these three cytoskeletal elements

Microtubule Motor Proteins: Kinesins (move toward + end) and Dyneins (move toward – end). Proteins move in opposite directions along the microtubule. Cilia and flagella: Dynein (+ end), nexin link (bend) Kartagener’s syndrome: no dynein Actin: stress fibers, cell cortex, filopodium, ms. Fibers, nerve cell, cytoplasm, cell surface Intermediate: cytoplasm epithelia, connective tissue, muscle, neuro, nerve cells Nuclear nuclear lamins in all nucleated cells Microtubules: axons in neurons, cytoplasm, cell surface

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