The cytoskeleton is composed of microtubules, microfilaments, and intermediate filaments that give cells their shape and allow cellular movement. Microtubules originate from the microtubule organizing center and extend towards the cell membrane. They are involved in many cellular functions like intracellular transport, cell division, and maintaining organelle structure. Microtubule associated proteins help stabilize microtubules and connect them to other cell components.

1. CYTOSKELETON

2. Cytoskeleton
• CELL = Cytosol + organelles + cytoskeleton
• Complex network of protein filaments ( strands ) that lines the
inside of the cell and gives its shape .

3. Funtions
• Determination and preservation of Cell/Nucleus shape and
placement (elasticity, strength)
• Movement of the cell (migration, diapedesis [leakage of
blood cells from the vessel walls into tissues], etc.),
movement of a part of the cell ( cilia , tail, etc.)
• Phagocytosis, endocytosis , exocytosis
• Cytokinesis
• Intracellular transport
• Contraction
• Supporting cell-cell and cell-extracellular media relationships
• Creating a structural framework within the cytoplasm
• Effective regulation of cell cytoplasm
• Stabilization of intercellular connections

4. Basic Elements of the Cytoskeleton
The cytoskeleton consists of 3 well-defined filament
structures:
1. MICRTUBULES (25 nm )
Tubulin (alpha, beta, gamma)
2. MICROFILAMENTS (7 nm )
Actin (F and G)
3. INTERMEDIATE FILAMENTS (10 nm )

5. Localizations
• Microtubules : They originate from the centrosome and are
extensions from the nucleus to the cell membrane.
• Microfilaments : They are located under the cell membrane
and have support functions.
• Intermediate Filaments : They are found distributed in the
cytoplasm of the cell.
microtubules
microfilaments
(actin filaments )
intermediate
filaments

6. 1. MICROTUBULES
• They are hollow cylindrical protein
structures without a membrane.
• 13 protofilaments coming together
from protein subunits with similar
structure .
• Protofilament It consists of alpha and
beta tubules .
• A third tubulin, gamma-tubulin,is
specifically located in the structure of
centrosomes and plays a critical role
in microtubule structure.

7. • Microtubules originate from centrosome.
• Microtubule organizing center (MTOC) including the centrosome their
formation begins.
• They extend from the MTOC (yellow in the figure) towards the cell
membrane.

8. Microtubule organizing center (MTOC)
• Gamma tubulin rings located in the centrosome region are
the formation centers.
• Tubulin to these areas Polymerization begins with the
addition of dimers .

9. microtubule polymerization depolymerization
• Tubulins are bound to GTP and GDP .
• Each tubulin The dimer carries two GTPs . One of these hydrolyzes to GDP
immediately after tubulin addition to the end of the microtubule.

10. Structures consisting
• Cilia (Singular: cilium )
• Whip
• Basal body
• Centrosome

11. CILIA
• The cilia of the cells in the respiratory organs of mammals
allow dust to be retained.
• 9+2 layout

12. TAIL
• 9+2

13. Basal Body: Triplet microtubule structure

14. CENTROSOME
 The centrosome consists of two centrioles .
 Each centriole consists of 9 microtubules in threes. occurs.

15. • Centrioles are connected to each other by various filamentous proteins.

16. Centrosome
• Centrosome is the microtubule regulatory center that binds to the
minus ends of microtubules .
• In the center of the interphase cells, adjacent to the nucleus.
• It plays a major role in determining the intracellular organization of
microtubules.
• It has an initiating role in the assembly of microtubules growing
from the centrosome towards the periphery of the cell..
• They become two pairs by pairing before cell division.
• During mitosis, they move to opposite poles and form spindle fibers.

17. cytoplasmic Structures of Microtubules and
Their Functions
1- Intracellular transport
– Organelle and vesicle transport
– axonal convection
– Transport of pigment granules
2- Organelle stability ( Golgi -ER)
3- Mitosis Shuttle Formation and Chromosome Movements
Participation in Cellular Structures as Stable Microtubules
– Cilia-Flagella and Movement
– Centriole -Basal Body

18. Organelle and Vesicle Transport
• Dinein : Provides transport towards the negative end .
• Kinesin: Provides transport towards the positive end .

19. Mechanism of intracellular transport by
dyneins and kinesins

20. Axonal transport
• Axonal transport is provided by dynein and kinesin .

21. Transport of pigment granules
• Melanin is a dark colored biological pigment normally found in the
skin, hair, eye membranes and some parts of the brain.
• Melanin pigment accumulated in melanosomes is transported within
the cell by dynein and kinesin .

22. Formation during Mitosis and Chromosome
Movements
• During mitosis , microtubules form spindle fibers.

23. • Three types of microtubule structures are formed during
mitosis:
1. Kinetekor MT
2. Polar MT
3. Astral MT

24. • The pulling of chromosomes or chromatids to opposite poles
occurs by depolymerization of microtubules from both ends.

25. Microtubule associated proteins
• Microtubule- associated proteins (MAP) bind microtubules
and increase their stability .
• microtubules to connect to other cell components and
intermediate filaments .
• A large number of MAPs were detected.
• The most studied are MAP-1, MAP-2 and Tau
(tubulin associated unit) , and MAP-4 in non-neuronal cells .
• A neuron; It has a cell body, an axon and dendrites .
• Axons and dendrites contain microtubules of certain polarity .
• Tau protein is a major component of the characteristic lesions
found in the brains of Alzheimer's patients.

26. MAP2 and Tau proteins: Connect two microtubules together.
• Axons, Taurus Contains protein.
• Dendrites , MAP-2 They contain.

27. MAP2 and Tau