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38 Cards in this Set

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What is the cytoskeleton?
An organized intracellular network of 3 protein filament types
What 3 protein filaments make up the cytoskeleton?
-Actin filaments
-Intermediate filaments
-Microtubules
What is the function of the cytoskeleton?
Provides mechanical support and movement of whole cells and the structures within them.
What is each component of the cytoskeleton composed of?
Actin filaments = globular Actin
Intermed fils = intermediate fibrous proteins
Microtubules = tubulin heterodimer subunits
How does the cytoskeleton behave?
Dynamically
What is a major difference between IF and Actins other than size?
Actin filaments are ATPases, IFs have no NTPase capability.
2 cell structures that are made up by intermediate filaments:
-Cell/cell desmosome junctions
-Cell/matrix junctions
What structures are Actin filaments found in?
-Cell/cell ADHERENS junctions
-Actin/myosin contractions
3 Important roles of IFs in cells:
-Form ropelike hammock to cradle the nucleus
-Give mechanical strength to cell
-Give structure to nuclear envelope
6 Types of Intermediate filaments:
DGKNNV
-Nuclear lamins
-Vimentin
-Desmin
-Glial fibrillary acidic protein
-Keratins
-Neurofilaments
In what type of cell would IFs be concentrated generally?
In cells under mechanical stress
What type of cell junctions involve IFs?
Desmosomes
What cancers are Keratin Positive?
-Breast
-GI
What cancers are Vimentin positive?
Sarcoma
What disease is caused by an autosomal dominant mutation of genes for Lamins A/C?
Emery-Dreifuss Muscular Dystrophy
Loss of which IFs will result in
-Loss of life
-Degraded function
Loss of life = lamins

All others just degrade function
Where exactly do Lamin Bs reside?
Attached to their lamin b receptors (LBR) on the nuclear side of inner nuclear membrane.
What is attached to Lamin B?
Lamins A/C - they interact w/ B on one side, and organize chromatin on their other side.
What happens when lamin B is phosphorylated?
It depolymerizes the lamins
Symptoms of EmeryDreifuss Muscular Dystrophy:
-Peripheral heterochromatin detached from inner nu membrane
-Progressive muscle weakness
-Joint contractures
-Cardiomyopathy
What results from genetic defect in Keratin genes?
Blistering disease which leads to infections
What function of IFs is essential for preventing blisters?
Its ability to distribute shear force across cells.
What is the name for blistering disease?
Epidermolysis bullosa simplex
What parts of IF molecules are:
-Conserved
-Variable
Conserved = alpha helical domains that allow subunits to bind to each other.
Variable = N and C-terminus ends
What do the variable N and C-terminal ends of IFs confer?
Diversity of function
How much IF in nondividing cells is free?
1-5%
How do soluble IF monomers assemble into dimers?
By packing to form a nonpolarized high-tensile, insoluble filament.
What do the IF filaments join togehter to form?
Staggared antiparallel tetramers
What mediates assembly and disassembly of IFs?
Phosphorylation and dephosphorylation
In which filaments is the N terminal essential for assembly?
-Vimentin
-Neurofilaments
-Lamins
How do IFs link to membranes and the cytoskeleton?
By IF binding proteins
What disease is mutated neurofilament protein a risk factor for?
Amyotrophic lateral sclerosis
Are IFs polarized or nonpolarized?
Nonpolarized
What is the structure of a homodimer of IFs like?
Parallel coiled-coil
What is the structure of the tetramer like?
Staggered tetramer of two Antiparallel coiled coil homodimers
How are neurofilaments crosslinked?
By their C-terminal extensions
Are IFs associated with motor proteins?
No
What happens when the globular heads of IFs are phosphorylated?
They disassemble