11.intermediate filaments - cell biology
TRANSCRIPT
Molecular & Cell Biology
S. Rahgozar,PhD
University of Isfahan
Faculty of Science
6. Cytoskeleton and Cell Movement
6.2. Actin /myosin & Intermediate Filaments
1392-93
(2.3 μm)
Actin-myosin complex in muscle Fibers
The additional proteins are titin and nebulin
A number of different types of actin binding proteins remodel
or modify existing filaments.
o Muscle Contraction
Sliding filament model of muscle contraction
Myosin II molecule
(catalytic core) (Lever arm)
+
Model for myosin action
Association of
tropomyosin and
troponins with
actin filaments in
striated muscles
After calcium release Before calcium release
Examples
Stress fibers
Adhesion belts in epithelial cells
Contractile ring
Actin-myosin complex in
Non muscle Fibers
1- Myosin II
Contractile assemblies of actin and myosin in non muscle cells
Regulation of Myosin II
MLCK: Myosin light-chain kinase
2- Myosin I
3- Myosin V
Formation of cell protrusions and cell movement
o Crawling of amoebas
o Migration of embryonic cells
during development
o Invasion of tissues by white blood
cells during infections
o Migration of cells involved in wound healing
o Spread of cancer cells during the metastasis of malignant tumors
o Phagocytosis
o Extension of nerve cells during development of the nervous system
Examples
Actin filament branching at the leading edge
Intracellular organization of
keratin filaments
Intermediate Filaments
Actin filaments’ diameter: 7 nm
Microtubules’ diameter: 25 nm
Intermediate filaments’ diameter: 8-11 nm
Assembly of intermediate filaments
Keratin fillaments attached to the dense plaques of intracellular protein on both sides of a
desmosome
Desmosomal cadherins (desmoglein and desmocollin) link adjoining cells to
intermediate filaments through plakogobin, plakophilin and desmoplakin
Various cell junctions found in a vertebrate epithelial cell
Small intestine of a vertebrate