Cytoskeleton Flashcards
Principle protein of microfilaments and microtubules
actin and tubulin respectively
Microfilaments are typically located as:
filament netwrok under plasma membrane, contractile bundle, and parallel bundles (stress fiber and cores for microvilli and stereocillia)
Microfilament structure
double helical arrangement of actin molecules
G-actin
unpolymerized
f-actin
polimerized, polar
Actin Polymerization
requires ATP and depends on local concentration of G-actin and other actin binding proteins… done as necessary for cell fxn
G/F actin ratio
always in equilibrium
“Treadmilling”
New molecules add preferentially to (+) end filament, others lost at (-) end = continuous flow actin from (+) end
to (-) end
How is actin arranged in the cell?
As a loose meshwork of crosslinked filaments typically found immediatelyunder and attached to the
plasma membrane. As bundles of parallel
filaments crosslinked by proteins such as fimbrin or villin
What is the crosslinking protein often associated with actin filaments specificlly in lood meshwork of crosslinked filaments
filamin
Microvilli
Microvilli are finger-like projections of the surface of some cells such as intestinal epithelial cells & have a core composed of a bundle of parallel
microfilaments
Cytochalasins B and D
These drugs bind (+) end of microfilament &
block addition of new actin molecules
Phalloidin
This drug stabilizes microfilament structure &
prevents depolymerization. Thus blocks cell activities requiring
reversible polymerization & depolymerization
Composition of microtubules
composed of tubulin a and B dimers, bind microtubule associated proteins
What molecule begins polymerization in microtubules
y-tubulin
Cytoplasmic vs. motor microtubules
cytoplasmic is more liable, has single tubules, and
microfilaments vs. microtubules source of energy for polymerization
microfilaments: ATP and microtubules: GTP
How are microtubules aligned in cells?
Because they have polarity, - end in the center associated with centrioles and + end in edges
Kinesin
moves along microtubule from - end to + end
Dynein
moves along microtubule from + end to - end
Colchicine
binds tubulin dimers & blocks their addition to tubule end
causing rapid depolymerization of the microtubules. Is used for treatment of gout.
Taxol
binds to tubulin in the intact microtubule & stabilizes the
microtubule. Is used in therapy for breast cancer.
Vinblastin and Vincristine
bind microtubule and are used as anti-
mitotic and anti-proliferative drugs in cancer therapy
Intermediate Filamens
cytoskeletal fxn, no large pools of monomers in equilibrium with filaments, chemically ressistant and stable
What control polymerization in intermediate filaments?
phosphorylation
What are the 6 major classes of intermediate filament proteins?
keratin, vimentin and vimentin like proteins, neurofilament protein, lamins, and beaded filaments
Filaggrin
binds keratin filaments into bundles
plectin family of proteins
bind microfilaments, microtubules, and
intermediate filaments into 3-D networks
Plakins
involved in binding of intermediate filaments to
hemidesmosomes, & actin filaments to neurofilaments of sensory neurons. Includes desmoplakins, desmoplakin-like proteins, and plakoglobulins
Lamins in intermediate filaments
strengthen the nuclear envelope
Where are intermediate filaments located in the cell
concntrated in a dense ring around nucleus and radiate to periphery
Where do intermediate filaments attach in epithilia?
attach to desmosome and hemidesmosome cell junctions as tonofilaments and strengthen layer
Fxns of microfilaments
anchorage and movement of membrane proteins, structural core of microvilli, locomotion of cels, extension of cell processes (filopodia and lamellopodia), cytoplasmic streaming, cytokinesis, and morphogenetic movements of tissues during embriology
Fxns of microtubules
intracellular vesicular transport and organelle movement, movement of cilia and flagella, chromosome movement, maintenance of cell shape, and maintenance of position of ER and intermediate filaments
