The document discusses the key components of the cytoskeleton - microtubules, microfilaments, and intermediate filaments - and how they work together to maintain cell shape, allow movement of organelles and vesicles, transport materials within the cell, and enable cell movement through polymerization and interaction with motor proteins like myosin and kinesin. The cytoskeleton is a dynamic network that forms various structures through accessory proteins and allows rapid changes in cell morphology.
2. 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 ?
3. Cytoskeleton: the skeleton of a cell
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Cells need a (cyto)skeleton to:
•create shape dynamic!
•change shape
•allow movement
4. 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
5. 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
6. Structure of actin filaments
Polymerization of actin
filaments
Organization of actin filaments
Actin binding protein
Function of actin filaments
7. 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
8. 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
9. 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
10. 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)
13. 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
14. 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
16. 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
17. 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
18. Types of intermediate filaments
According to protein subunit, Intermediate filaments in the cytoplasm can be
grouped into:
19. 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
20. Function of intermediate filament
Tensile strength cells enable to withstand the
mechanical stress (streched)
Provide stuctural support for the cell
21. 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
22. The structure of
microtubules
Assembly of mirotubules
Microtubule function
Microtubule association with
motor protein
Structure and function of
cilia and flagella
23. 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
24. 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
25. 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
29. Function of microtubules
Pair of centrioles
organize microtubules guiding chromosomes in
cell division
30. 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
31. Cilia
Cilia = numerous & short (hair-like)
Oar-like movement
alternating power & recovery strokes
generate force perpendicular to cilia’s axis
32. 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
36. Distribution of different cytoskeletal elements
in the same cell
actin filaments (F-actin) intermediate filaments (IF) microtubules MT)
(rhodoamin-phaloidin) (anti-vimentin) (anti-tubulin)