Digital Dialogues: Speaking Activities, Web Tools & Apps (All Ages)
cytosceleton
-
Upload
wayan-sugiritama -
Category
Education
-
view
2.654 -
download
1
description
Transcript of cytosceleton
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
•change shape
•allow movement
=
dynamic!
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 withfilaments able to grow and shrink rapidly
Accessory proteinsRegulate 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 proteinActin bundling protein : hold actin filaments together in parallel bundle (microvilli)
Cross-linking protein : hold actin filaments in a gel-like meshwork (cell cortex)
Actin binding proteinFilament-seve ring protein : convert actin gel to a more fluid state (gelsolin)
Motor protein
Organization of microfilamentsMicrofilaments can organized in many forms :
Skeletal muscle : paracrystalline array integrated with myosin filaments
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
Organization of microfilaments
microvilli contractile bundles
in the cytoplasm
lamellipodia
filopodia
contractile ring
during
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
According to protein subunit, Intermediate filaments in the cytoplasm can be
grouped into:
Types of intermediate filaments
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 βtubulin
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 PartsMotor Molecules – requires ATP
Intracellular transport
microtubules
kinesins
dyneins
actin filaments
myosins
Function of microtubules
Pair of centriolesorganize 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
So….
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 elementsin the same cell
actin filaments (F-actin)
(rhodoamin-phaloidin)
intermediate filaments (IF)
(anti-vimentin)
microtubules MT)
(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 !