Cytoskeleton

cytoskeletal

1. PREPARED BY :-
PRIYANKA YADAV
M.Sc. Life sciences Ist
sem

2. INTRODUCTION
HISTORY TIMELINE
STRUCTURE
FUNCTIONS
CYTOPLASMIC FILAMENTS
INTERMEDIATE FILAMENTS
MICROTUBULES
MICROFILAMENTS
DIFFERENCES
SUMMARY
CONTENTS :

3. TYPICAL EUKARYOTIC CELL

4. INTRODUCTION
This is a scan of the first electron micrograph taken intact of eukaryotic cell.

5. CYTOSKELETON
The cytoskeletonis the structure consisting of fibrous proteins that occur
in the cytoplasm and maintain the shape of the cell.

7. History Timeline
•1942Discovery of actomyosin
•1954Sliding filament model for muscle contraction
•1965Dynein, the first microtubule-dependent motor
•1968–1978Identification of intermediate filaments
•1972–1977Actomyosincontractile ring in cytokinesis
•1973Isolation of the first non-conventional myosin
•1984Microtubule dynamic instability
•1989 & 1995g-Tubulin and microtubule-organizing centres
•1973Isolation of the first non-conventional myosin
•1984Microtubule dynamic instability
•1989 & 1995g-Tubulin and microtubule-organizing centres

8. STRUCTURE
•Network of filamentous proteins
•filaments formed from a few proteins
•monomer protein forms polymer filaments
•located in nucleus and cytoplasmic compartments
•not within organelles
•location based upon cellular function
•named on basis of physical size

9. FUNCTIONS :
functions based upon the filaments physical properties
integral strength
cell shape
motility
1.inside the cell
2.whole cell
3.motor proteins associated with 2 filamentsystems

10. signal transduction
Note -the Extracellular Matrix has a similar structural role
outside of the cell.

11. Cytoskeletal filaments:
1.Microfilaments
2.Microtubules
3.Intermediate
filaments

12. INTERMEDIATE FILAMENTS
different cell types, different intermediate filaments
all eukaryotes nuclear cytoskeleton the same
resist stresses applied externally to the cell cytoplasm
10-nanometer diameter
cross-linking proteins allow interactions with other cytoskeletal
networks

13. intermediate filament associated proteins (IFAPs)
coordinate interactions between intermediate filaments
and other cytoskeletal elements and organelles,
human disorders
mutations weaken structural framework
increase the risk of cell rupture

17. Intermediate filaments provide mechanical strength and
resistance to shear stress.
There are several types of intermediate filaments, each
constructed from one or more proteins characteristic of it.
Some functions of Intermediate Filaments :

18. MICROTUBULES
25 nm diameter, 14 nm internal channel tubulin cytoplasmic
All cells contain
Same core structure
Same motors Dynein (-) and Kinesin(+)
Different associated proteins
Dynamic
Continuous remodelling

19. Movement
Intracellular > cellular
Cell division mitotic spindle
Specialized structures
centrosome,Spindlepole
Cell processes -cilia (9+2)

20. MICROTUBULE STRUCTURE

21. STRUCTURE OF MICROTUBULE

22. If the rate of GTP hydrolyses is
faster then the rate of polymerization
, the microtubule will disassemble
(GTP cap is lost)
If the rate of polymerization is
faster than the rate of GTP
hydrolysis, the microtubule will
grow(It contains a GTP cap)

23. Microtubules participate in a wide variety of cell activities.
Most involve motion that is provided by protein “motors”
that use ATP.
They determine the positions of membrane-enclosed
organelles and direct intracellular transport.
The migration of chromosomes during mitosis and meiosis
takes place on microtubules that make up the spindle fibers.
SomefunctionsofMicrotubules:

24. MICROFILAMENTS
Twisted chain 7 nm diameter
most abundant protein in cells (5% of all cell protein)
Motility
Adhesion
Actin binding proteins
myosin motors
Muscle actins

28. CELL CRAWLING DEPENDS ON ACTIN

29. FORMINS –promotes the addition of G actin to the end of an unbranched filament
ACTIN BINDING PROTEINS

32. Actin filaments are anchored to the Z-disc at their + ends
The actin filaments face each other in the sarcomere
Upon contraction, the myosin heads moves towards the + end
Pulls the actin filaments towards each other.
MUSCLE CONTRACTION

33. Some functions of actin filaments are:
-To provide mechanical strength to the cell by forming a
band under the plasma membrane
-Link transmembrane proteins to cytoplasmic proteins
-Form contractile ring during cytokinesis in animal cells
-Cytoplasmic streaming
-Generate locomotion in cells such as white blood cells and
amoeba
-Interact with myosin to provide force of muscular
contraction

34. DIFFERENCES

35. •The cytoskeleton organizes the structures and activities of the cell.
•The cytoskeleton interacts with motor proteins.
•The cytoskeleton also plays a major role in cell motility.
•There are three main types of fibers in the cytoskeleton: microtubules,
microfilaments, and intermediate filaments.
•Microtubules, the thickest fibers, are hollow rods about 25 microns in
diameter.
SUMMARY

36. •Microfilaments, the thinnest class of the cytoskeletal fibers, are solid rods of
the globular protein actin.
•Microfilaments are designed to resist tension.
•Intermediate filaments, intermediate in size at 7nanometers, are specialized
for bearing tension.
•Intermediate filaments are more permanent fixtures of the cytoskeleton than
are the other two classes.