The cytoskeleton is a network of fibers in the cytoplasm that organizes cellular structures and activities through three types of molecular components: microfilaments, microtubules, and intermediate filaments. Microfilaments are involved in motility and shape maintenance, microtubules guide organelle movement and chromosome separation, while intermediate filaments provide structural support. Additionally, the extracellular matrix and intercellular junctions play crucial roles in cellular adhesion and communication.

1. Name – Pradeep Kumar

2.  The cytoskeleton is a network of fibers extending throughout the
cytoplasm
 It organizes the cell’s structures and activities, anchoring many
organelles
 It is composed of three types of molecular structures:
 Microfilaments
 Microtubules
 Intermediate filaments

3. Microfilaments:
 Actin
7nm
Microtubules:
 Tubulins (a, b)
25 nm
Intermediate filaments:
 Lamin
 cell specific prot. (e.g.
Vimentin)
8-12 nm
Microfilament

4.  The cytoskeleton helps to support the cell and maintain
its shape
 It interacts with motor proteins to produce motility
 Inside the cell, vesicles can travel along “monorails”
provided by the cytoskeleton
 Recent evidence suggests that the cytoskeleton may
help regulate biochemical activities

5. Properties Microfilament Microtubules Intermediate
filaments
Subunits incorporated
into polymer
ATP - actin
monomers
GTP - αβ - tubulin
heterodimer
Various globular
proteins
Preferential site of
incorporation
+ End barbed + End β - tubulin Internal
Polarity Yes Yes No
Enzymatic activity ATPase GTPase None
Motor proteins Myosin's Kinesins, Dyneins None
Major group of
associated proteins
Actin – binding
proteins
Maps Plakins
Structure
Flexible, helical
filament
Stiff, hollow tube Tough, ropelike fibers
Dimensions 8 nm diam. 25 nm outer diam. 10 nm diam.
Distribution All eukaryotes All eukaryotes Animals
Primary functions Motility, contractility
Support, intracellular
transport, cell
organization
Structural support

6. ATP-actin monomers

7. 10 µm
Column of tubulin dimers
Tubulin dimer 
25 nm

8. Fibrous subunit (keratins
coiled together)
8–12 nm
5 µm
Keratin proteins

9. Tissue level
Muscle
movement
Determines shape of
the cell
Motility of the cells
Cell adhesion
 Mitosis, meiosis
Cellular level
Subcellular level
Anchors organelles
Organization of organelles
Provides tensile strength
 Movement of
chromosomes
Organizing cell polarity
Intracellular movement of
vesicles
 Endocytosis – clathrin-
mediated endocytosis and
phagocytosis
Dynamic
Adaptable
Stable
Strong

10. o Cytoskeletal filaments are all constructed
from smaller protein subunits
o All form as helical assemblies
of subunits
o Noncovalent interactions: rapid assembly
and disassembly

12. Intermediate filaments- resistant to stretching forces

13.  Microfilaments are solid rods about 7 nm in diameter,
built as a twisted double chain of actin subunits
 The structural role of microfilaments is to bear tension,
resisting pulling forces within the cell
 They form a 3-D network called the cortex just inside
the plasma membrane to help support the cell’s shape
 Bundles of microfilaments make up the core of
microvilli of intestinal cells.

14. Microvillus
Plasma membrane
Microfilaments (actin
filaments)
Intermediate filaments
0.25 µm

15. F-actin
G-actin
Two parallel protofilaments
that twist around each other in
a right-handed helix

16.  Microfilaments that function in cellular motility contain the
protein myosin in addition to actin
 In muscle cells, thousands of actin filaments are arranged parallel
to one another
 Thicker filaments composed of myosin interdigitate with the
thinner actin fibers
 Myosin molecules walk along the actin filament, pulling stacks of
actin fibers together and shortening
the cell.

18. o Localized contraction brought about by actin and myosin also
drives amoeboid movement
o Pseudopodia (cellular extensions) extend and contract through
the reversible assembly and contraction of actin subunits into
microfilaments
 Cytoplasmic streaming is a circular flow of cytoplasm within
cells
 This streaming speeds distribution of materials within the cell
 In plant cells, actin-myosin interactions and sol-gel
transformations drive cytoplasmic streaming

19. Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
(b) Amoeboid movement
Nonmoving cortical
cytoplasm (gel)
Chloroplast
Cell wall
Streaming
cytoplasm
(sol)
Parallel actin
filaments
(c) Cytoplasmic streaming in plant cells
Vacuole

20.  Microtubules are hollow
rods about 25 nm in
diameter and about 200 nm
to 25 microns long
 Functions of microtubules:
 Shaping the cell
 Guiding movement of
organelles
 Separating chromosomes
during cell division

21. Interphase cell
Dividing cell
Neuron
centrosome
Basal body
Cilla
spindle
centrosome
axon
-Centrosome
-Cilia / flagellum
-Mitotic system
- Vesicular transport

23. o In many cells, microtubules grow out from a centrosome near the
nucleus
o The centrosome is a “microtubule-organizing center”
o In animal cells, the centrosome has a pair of centrioles, each with
nine triplets of microtubules arranged in a ring

24. 5 µm
Direction of swimming
(a) Motion of flagella
Direction of organism’s
movement
Power stroke Recovery stroke
(b) Motion of cilia
15 µm
 Cilia and flagella share a
common ultrastructure:
 A core of microtubules sheathed
by the plasma membrane
 A basal body that anchors the
cilium or flagellum
 A motor protein called dynein,
which drives the bending
movements of a cilium or
flagellum

26. Role of the dynein arms in beating cilia
Telescopic effect Beating

27.  Intermediate filaments range in diameter from 8–12 nanometers, larger
than microfilaments but smaller than microtubules
 They support cell shape and fix organelles in place
 Intermediate filaments are more permanent cytoskeleton fixtures than the other
two classes
 The extracellular matrix (ECM) of animal cells
 Intercellular junctions

31.  Animal cells lack cell walls but are covered by an elaborate
extracellular matrix (ECM)
 The ECM is made up of glycoprotein's such as collagen,
proteoglycans, and fibronectin
 ECM proteins bind to receptor proteins in the plasma membrane
called integrins
 Functions of the ECM:
 Support
 Adhesion
 Movement
 Regulation

32. EXTRACELLULAR MATRIX (ECM)

33.  Neighboring cells in tissues, organs, or organ systems often
adhere, interact, and communicate through direct physical
contact
 Intercellular junctions facilitate this contact
 There are several types of intercellular junctions
 Plasmodesmata
 Tight junctions
 Desmosomes
 Gap junctions

34.  Plasmodesmata are channels
that perforate plant cell walls
 Through plasmodesmata, water
and small solutes (and
sometimes proteins and RNA)
can pass from cell to cell

35.  At tight junctions, membranes of neighboring cells are pressed
together, preventing leakage of extracellular fluid
 Desmosomes (anchoring junctions) fasten cells together into
strong sheets
 Gap junctions (communicating junctions) provide cytoplasmic
channels between adjacent cells

37. Thank you