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.

1. Dr. I Wayan Sugiritama

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
=
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)

11. Actin binding protein
Filament-seve ring protein :
Motor protein
convert actin gel to a more fluid
state (gelsolin)

12. Organization of microfilaments
Microfilaments can organized in many forms :
 Skeletal muscle : paracrystalline array integrated with
myosin filaments

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

15. Structure of IF
Types of IF
Function of IF
IF binding protein

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

26. Molecular motors
microtubules actin filaments microtubules

27. Motility of the Cell and Its Parts
 Motor Molecules – requires ATP

28. Intracellular transport
actin filaments
microtubules myosins
kinesins
dyneins

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

33. How does it work?
Dynein Arms

34. So….

35. Summary
 Microtubules
 thickest
 cell structure & cell motility
 tubulin
 Microfilaments
 thinnest
 internal movements
within cell
 actin, myosin
 Intermediate filaments
 intermediate
 more permanent fixtures
 keratin

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)

37. Cytoskeletal elements in eukaryotes

38. Rapid changes in cell morphology associated with a
dynamic cytoskeleton
Inactive platellet Active (spread) Active (contract)

39. Without the cytoskeleton ?
Wounds would never heal !
Muscle would be uselless !
Sperm never reach the egg !