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 CYTOSKELETON II
 Intermediate Filaments
Prof. Dr. Müjgan CENGİZ
 Intermediate Filaments
1. Their diameter about 10 nm(actin 7,microtubul
25 nm)
2. All eukaryotic cells contain actin and tubulin
3. They Found only at metazoans (vertebrates,
nematodes, mollusca).
4-They are not involved in cell movement.
They play structural role by provide mechanical
stres.
They have rope like character.
They can easily bent but difficult to break.
Actins and microtubuls polymers of single type
proteins, İntermediate filaments different types
of proteins.
 Major function is to supply physical strength to the cells
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and tissues.
Plentiful in neronal aksons.
There are more than 50 different Int. Filament.
They are identified and classified into six groups .
Classification based on similarities of their amino acids.
 There are 2 types of keratins(they are used for
production of hair nails and corns).
 Acidic keratins(type I), basic/neutral keratins(type II).
20 different types of human epitel cells exist
 10 type more specific for hair and nails.
 Some types of type I and II keratins called (hard
keratins)(hair, nail and corn)
 The types of type I and II keratins called(soft keratins)
Abundant in epthelial cells.
 The type III IF include vimentin.
 Type IV NF include 3 type of proteins(L;H;M).Major
NF of mature neurons
 ɑ internexin expressed early stage of neuron
development

Cooper,G.M: The Cell. A molecular Approach 2nd edition. Boston university. Sunderland(MA). Sinauer Associates,2000
L
Cross linked keratin networks held together
with S-S bond.
They may survive even after death of the cells.
Disease about keratin Epidermolysis bullosa
simplex (mutation in keratinType 14).
(defective keratins expressed in the basal layer
of the epidermis).
ALS (amylotropic lateral sclerosis. Loss of
motor neurons)
Microtubules
1. Microtubules are polymers of protein tubulin
2. Tubulin is a dimer made up of two closely related a and b
tubulin. 55kd
3. Dimers aggregate head to tail to form parallel arrays of
protofilaments.
4. Microtubules consist of 13 linear protofilaments assembled
around a hollow core
Function of Microtubules
1. Cell shape
2. Self locomotion
3. Intracellular transport of organelles
4. Separation of chromosomes during mitosis
Polarity of Microtubules
1. Microtubules like actin filaments are polar
structures with two distinct ends, fast growing
and slow growing.
2. Polarity is important consideration in
determining the direction of movement along
microtubules just like the polarity of actin
filament, which defines the direction of myosin
movement.
Stabilization of Microtubules and cell
polarity
 Dynamic behaviour of the microtubules is
regulated by
 1-Ca Low con of the Ca increases
polymerization(1.10-6)
 2-MAPs –Microtubul associated proteins.
 Map1, Map2, Map3, Map4(bins the microtubuls
and inhibit dis.of tubulin)
 3-Tau proteins. Only one Tau gene 64 different tau
protein)
Drugs which bind tubulin:
Colchicine
Colcemid
Vincristine
Vinblastine
Inhibit polymerization
And thus selectively inhibit
Cell division
Taxol
Stabilizes microtubules and also
Blocks cell division
Anti-Cancer Drugs
Vinblastine and vincristine bind tubulin and inhibit
polymerization. They inhibit selectively rapidly
dividing cells.
Taxol stabilizes microtubules rather than inhibiting
their assembly. Such stabilization blocks cell
division
Amantia falloides is a mushroom and falloidin
isolated from it. It binds to the aktin and increazes its
polymerization.
Motor Proteins in Cytoskeleton
1. Myosin - Translocates along actin toward positive
ends
2. Kinesin - Translocates along microtubules toward
positive ends
3. Dynein - Translocates along microtubules toward
negative ends
Properties of Dynein
• 2000 kd protein
•
2 or 3 heavy chains with a number of light chain
and intermediate polypeptides.
• Globular head domains are motor domains which
bind ATP
• Dynein occurs in several forms but all move
along microtubules toward minus ends
Properties of Kinesin
•
Kinesin head (340 AA) and myosin head (850 AA) domains are
structurally similar. From the common ancestor.
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This portion is responsible for binding to other cell component.
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100 other kinesin proteins have known.
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Some move along microtubules toward the positive and some
towards the negative ends.
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Different tail sequences - move different cargo types - vesicles,
organelles and chromosomes.
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CENTROSOME
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Centrosome is the microtubule organizing(MOC) center
in which the minus ends of microtubules are anchored. It
is located adjacent to the nucleus near the center of the
interphase cells.
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Centrosome plays a big role in determining the
intracellular organization of microtubules.
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Centrosome serves as the initiation role of the assembly of
microtubules which grow outward from the centrosome
toward the periphery of the cell.
Organization of Microtubules in Nerve Cells
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A neuron has a cell body, an axon and dendrites
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Axons and dendrites contain microtubules in certain
polarity
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Both contain specific MAP proteins
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Axons contain tau protein and no MAP-2
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Dendrites contain MAP-2 and no tau
•Microtubule associated proteins (MAP) bind to
microtubules and increase their stability
•There are alot of of MAPs have been identified. Most well
known are, MAP-1, MAP-2 and tau and MAP-4 in nonneuronal cells.
•The tau protein is the main component which found in the
brains of Alzheimer patients.