Published on June 23, 2009
Dr. I Wayan Sugiritama
QUESTIONS: How cell maintain their shape ? How cell organize its organelles? How cell transport vesicles? How the segregation of chromosomes into daughter cells at mitosis ? How epithelial cell can withstand to the mechanical stress? How spermatozoa can reach the eggs ? How leucoyte can move to the extracelluler space ?
Cytoskeleton: the skeleton of a cell = Cells need a (cyto)skeleton to: •create shape dynamic! •change shape •allow movement
CYTOSKELETON Complex network of : Microtubules Intermediate filaments And actin filaments Provide for : The shaping of the cells Movement of organelles and intracytoplasmic vesicles Movement of entire cells
General properties of cytoskeleton elements All are protein polymers Dynamic structures with filaments able to grow and shrink rapidly Accessory proteins Regulate polymerization and depolymerization Regulate function
Structure of actin filaments Polymerization of actin filaments Organization of actin filaments Actin binding protein Function of actin filaments
Structure of actin filaments Composed of two chains of globular subunit (G-actin), coiled each other to form a filamentous prot. (F-actin) Thinnest class of fibers (6 nm thick) Has stuctural polarity Associated with a large number actin- binding protein variety of organization and function Depending on isoelectric point : α-actin of muscle β-actin & γ-actin of non muscle
Actins polymerization Actin filaments can grow by addition of actin monomer at either end When filament reach desire length, capping proteins attach to the plus end and terminating polymerization 8
Actin monomer binding proteins Control pool of unpolymerized actin Two proteins Profilin Inhibits addition of monomers to pointed (slowgrowing) end Thymosin β4 If a filament is capped at both ends it is effectively stabilized
Actin binding protein Actin bundling protein : hold Cross-linking protein : hold actin filaments together in actin filaments in a gel-like parallel bundle (microvilli) meshwork (cell cortex)
Actin binding protein Filament-seve ring protein : Motor protein convert actin gel to a more fluid state (gelsolin)
Organization of microfilaments Microfilaments can organized in many forms : Skeletal muscle : paracrystalline array integrated with myosin filaments
Organization of microfilaments Non muscle cells : Cell cortex : form a thin sheath beneath the plasmallema Associated with myosin form a purse string ring result in cleavage of mitotic cells contractile ring microvilli contractile bundles lamellipodia during in the cytoplasm filopodia cell division
Actin and cell locomotion Three steps : The cell pushes out protrution at its front (lamellipodia & filopodia) Actin polymerization These protrution adhere to the surface Integrins adhere to the actin filaments and the extracellular matrix on the surface The rest of the cell drags itself forward Interaction actin filaments with myosin
Structure of IF Types of IF Function of IF IF binding protein
Structure of Intermediate filaments • Ropelike with many long strands twisted together • The subunit are elongated fibrous proteins (many types) • Intermediate in size 8- 12nm • Form a network troughout the cytoplasm and surrounding nucleus
Polymerization of Subunit structure •The subunit : •N-terminal globular head •C-terminal globular tail •Central elongated rod domain •The subunit form stable dimer •Two dimer form tetramer •Tetramer bind to one another and-to-end generate ropelike
Types of intermediate filaments According to protein subunit, Intermediate filaments in the cytoplasm can be grouped into:
Intermediate filament binding protein Link, stabilized and reinforced the intermediate filaments into three-dimensional network : Fillagrin : binds keratin filaments into bundles Synamin & Plectin : binds desmin & vimentin, links intermediates filaments to microtubules, actin and desmosome Plakins : maintenance of contact between keratin and hemidesmosomes of epithelial cells
Function of intermediate filament Tensile strength cells enable to withstand the mechanical stress (streched) Provide stuctural support for the cell
Function of intermediate filament Form a deformable three-dimensional structural framework for the cell Rreinforce cell shape & fix organelle location The nuclear envelope is supported by a meshwork of intermediate filaments
The structure of microtubules Assembly of mirotubules Microtubule function Microtubule association with motor protein Structure and function of cilia and flagella
Structure of Microtubules Hollow tube about 25 nm in diameter The subunit is heterodimer α and β tubulin Polarized : having plus end & minus end Dynamic structure : grow or shrink as more tubulin molecules are added or removed
Polymerization of microtubules Microtubules are form by outgrowth from MOC (exp. the centrosome) Centrosome contains γ- tubulin ring; serve as starting point for growth Αβ-tubulin dimers add to the γ-tubulin form hollow tube Polymerization more rapid in plus end
Function of microtubules Microtubules participate in the intracellular transport of organelles and vesicles Axoplasmic transport of neuron Melanin transport Chromosome movement by mitotic spindle Vesicle movement among different cell compartments Under control by motor protein
Molecular motors microtubules actin filaments microtubules
Motility of the Cell and Its Parts Motor Molecules – requires ATP
Intracellular transport actin filaments microtubules myosins kinesins dyneins
Function of microtubules Pair of centrioles organize microtubules guiding chromosomes in cell division
Cilia & Flagella Motile processes, with higly organized microtubule core Core consist of 9 pairs of microtubules arround 2 central microtubule (axoneme) bending of cilia & flagella is driven by motor protein (Dynein) At the base is basal body, that control the assembly of the axoneme
Cilia Cilia = numerous & short (hair-like) Oar-like movement alternating power & recovery strokes generate force perpendicular to cilia’s axis
flagella Flagella = 1-2/cell & longer (whip-like) move unicellular & small multicellular organisms by propelling water past them undulatory movement , force generated parallel to flagellum’s axis cilia sweep mucus & debris from lungs flagellum of sperm cells
How does it work? Dynein Arms
Summary Microtubules thickest cell structure & cell motility tubulin Microfilaments thinnest internal movements within cell actin, myosin Intermediate filaments intermediate more permanent fixtures keratin
Distribution of different cytoskeletal elements in the same cell actin filaments (F-actin) intermediate filaments (IF) microtubules MT) (rhodoamin-phaloidin) (anti-vimentin) (anti-tubulin)
Cytoskeletal elements in eukaryotes
Rapid changes in cell morphology associated with a dynamic cytoskeleton Inactive platellet Active (spread) Active (contract)
Without the cytoskeleton ? Wounds would never heal ! Muscle would be uselless ! Sperm never reach the egg !
Intermediate filaments are a part of the cytoskeleton of all animals. These filaments, averaging 10 nanometers in diameter, are more stable (strongly bound ...
Cytoskeleton, Inc. G-LISA, Activation assay, Actin, Tubulin, RhoA protein, signal transduction, cofilin, profilin, phalloidin, myosin, kinesin, GLISA.
Übersetzung für cytoskeleton im Englisch-Deutsch-Wörterbuch dict.cc.
cytoskeleton [si″to-skel´ĕ-ton] a conspicuous internal reinforcement in the cytoplasm of a cell, consisting of tonofibrils, filaments of the terminal ...
Cytoskeleton, Inc, manufacturer of high quality kits and reagents such as Signal Seeker Kits and Proteins, GOBlot™ Western Blot Processor, Actin Research ...
The machinery that powers cell migration is built from the actin cytoskeleton, which is larger than any organelle. When a fibroblast is observed by ...
Kostenloses eBook: Cytoskeleton als Gratis-eBook Download bei Weltbild. Jetzt kostenloses eBook sichern und in unserem Sortiment stöbern!
Bücher bei Weltbild: Jetzt The Cytoskeleton versandkostenfrei online kaufen & per Rechnung bezahlen bei Weltbild, Ihrem Bücher-Spezialisten!
The cytoskeleton is found inside eukaryotic cells attached to the cell membrane. It is essentially the 'skeleton of the cell'. The main ...
Universität Leipzig: Cytoskeleton (englisch) (Memento vom 2. April 2009 im Internet Archive) Zytologie-online.net: Information über das Cytoskelett der ...