7 CBLG311 S2017 - cytoskeleton (1).pptx - THE CYTOSKELETON...

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THE CYTOSKELETON CHAPTER 16 1
LECTURE SECTION:  THE CYTOSKELETON 2 1. Cytoskeleton types and properties Actin Microtubules 2. Cytoskeletal functions Static and dynamic functions 3. Cytoskeletal filaments and protofilaments Subunit interactions Nucleation 4. Cytoskeletal Structure G-actin and F-actin Tubulin and Microtubules 5.Filament polymerization and depolymerization rates Rates Critical concentration Plus and minus end behaviour & kinetics Nucleotide-binding  Treadmilling Dynamic Instability  6. Motor Proteins Myosins, Kinesins and Dyneins Coupling ATP-hydrolysis to movement Muscle organization Intracellular organelle movement 7. Cytoskeletal Regulation See Panel 16.3 Nucleation Cytoskeletal binding proteins 8. Cytoskeletal higher-order structures Bundling Cross-linking
3 Types of Cytoskeleton: Actin Filaments Actin filament (microfilament): 2-stranded helical non-covalent polymer of globular (G-actin) actin 5-9 nm in diameter Linear bundles, 2-D and 3-D networks Cell shape Cell movement and force
4 Types of Cytoskeleton: Microtubules Microtubules: Cylindrical non-covalent polymer of tubulin Originate from the microtubule- organizing center (MTOC) Cell shape and movement Cell division Membrane trafficking and intracellular distribution of organelles
5 Cytoskeletal functions in: 1. Dynamic processes (undergo rapid changes): Cell motility Phagocytosis Cell division Cell contraction Intracellular transport 2. Static processes (undergo very slow changes): Epithelium tissue Neuronal networks Nuclear envelope Cytoskeleton is dynamic and adaptable
6 Cytoskeletal changes during cell division Red = actin Green = microtubules 1. Actin filaments form the contractile ring that splits the cell in cytokinesis 2. Microtubules form the mitotic spindle that separates chromosomes during mitosis When cells enter cell cycle:
7 Cytoskeletal functions in: 1. Dynamic processes (undergo rapid changes): Cell motility Phagocytosis Cell division Cell contraction Intracellular transport 2. Static processes (undergo very slow changes): Epithelium tissue Neuronal networks Nuclear envelope
8 Epithelium: Stable and strong cytoskeleton network Actin = forms microvilli that increase surface area of cells and stabilize tight junctions Microtubules = form “transport” tracks from one end to the other in epithelial cells Intermediate filaments = stabilize cell connections called desmosomes
9 Cytoskeleton: dynamic, rapid changes e.g.: phagocytosis Cytoskeleton: slow, lasting structures e.g. epithelium Same type of cytoskeleton in both cases! So, how can this be? Cytoskeleton is not cement! It is dynamic – maintain or change size, stability, strength, etc How? Because they are made of subunit building blocks
10 Cytoskeletal filaments are built from monomer protein subunits Fig. 16-7 Assembly and disassembly of filaments is regulated Held by non-covalent bonds unlike polymers like nucleic acids (however note that each “building block” is itself a protein)
Image courtesy of Thomas P. Stossel (Brigham and

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