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Information about cytosceleton

Published on June 23, 2009

Author: sugiritama



power point contains: structure and function of microtubules, intermediate filaments and actin filaments

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 !

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