Cytoskeleton Flashcards
Width of actin filament
7 nM
Polarization of actin
Grow fastest at + end, depolymerize at - end
Polymerization of actin
G actin binds to ATP
Polymerizes into F-actin (mostly at + end)
ATP later hydrolyzes to ADP
Polymerization also requires K+ and Mg+
Structure of actin
G = granular, polymerizes into F (fibrillar) in presence of ATP
Functions of actin
Anchor membranes, structure (terminal web)
Contractile (shape, movement, cell separation)
Transport around cell (actin binding proteins)
Form microvilli, lamellae, filopodia
Actin and ATP cycling
Requires ATP presence to polymerize (reflects concentrations of ATP in cell)
Hydrolysis while polymerized
ADP tends to depolymerize
Actin binding proteins (6)
Myosin - motor Tropomyosin - stabilizes Gelsolin - breaks filaments in middle Actin bundling proteins - fimbrin, villin, alpha actinin Branching proteins - formin Integrin - intermembrane, anchors to ECM
Actin and cell movement
Polymerization can move cell membrane
Myosin can be bound to organelle, vesicle or to membrane
Actin disrupters
Cytochalasins B+D - prevent polymerization (chemo)
Phalloidin - prevents depolymerization (mushroom toxin)
Microtubule size
25 nM (biggest cytoskeleton element)
Microtubule structure
Tubulin dimers (alpha and beta) in
13 chains around
hollow core
Originate from MTOC
Microtubule polarization
- end at MTOC
+ end at periphery - growth and depolymerization at + end (MTOC caps - end)
Microtubules and GTP cycling
GTP binding promotes assembly
Depolymerizes closer to bottom
MTOC
AKA centrosome
Nine sets of triplets of MTs
Rings of gamma tubulin and capping proteins that stabilize - end of all microtubules
Functions of microtubules
Organize and transport organelles (vesicles, Golgi, ER)
Mitosis (create spindle)
Can contribute to cell movement and shape
Cilia
Microtubule movement
Kinesins to + end
Dynein to - end
Both are ATPases (bind for conformational change, hydrolisis for release and resetting)
Responsible for relative movement (ie cilia)
Cilia structure
9 doublets + 2 central MTs
Dynein attach to next doublet, bend and release for movement
Basal body is 9 triplets (like MTOC)
Microtubule disruptors
Vinblastine - chemo, prevents polymerization
Taxol - chemo, stabilizes (prevents mitosis)
Colchicine - gout, prevents polymerization (decreases inflammatory cell movement)
Size of intermediate filaments
8-10 nm
Intermediate filament structure
2 coiled dimers form tetramer
8 staggered tetramers form filament
Characteristics of intermediate filaments
Non-polar (each tetramer is symmetrical)
Don’t regularly (de)polymerize
Very stable and strong
Types of intermediate filaments (6)
Keratin - epithelia Vimentin - connective tissue, mesenchyme Desmin - skeletal muscle Glial fibrillary acidic protein - glial cells Neurofilaments Lamins - all nuclei
- Type of intermediate filament can identify cancer cell origins
- Helical/rod domain is conserved, ends have identifiable differences
Functions of intermediate filaments
Key for structure, mechanical stress (ie desmosomes)
Support other cytoskeleton elements
Lamin supports nuclear envelope
