MoCell Exam 2

cytoskeleton

complex, dynamic network of interlinking protein filaments in the cytoplasm of all cells

3 types of protein filaments in the cytoskeleton

actin filaments, microtubules, and intermediate filaments

actin filaments

helical polymers of the protein actin; aka microfilaments

microfilament structure

two parallel strands forming a helix

stress fibers

contractile bundles that play a role in cell adhesion, motility, and mechanosensing; often associated with focal adhesions

mechanosensing

ability of a cell to perceive and respond to mechanical forces

extracellular matrix (ECM)

network consisting of extra cellular macromolecules and minerals that provide structural and biochemical support to surrounding cells

focal adhesions

proteins that connects a cell’s cytoskeleton to the ECM

plus (+) end of an actin filament

barbed end; fast-growing end; hydrophobic/ABP-binding cleft

minus (-) end of an actin filament

pointed end; slow-growing end; ATP-binding cleft

ATP-actin

binds to (+) end of microfilament; polymerization

ADP-actin

dissociates from the (-) end of microfilament; depolymerization

phases of microfilament polymerization

nucleation, elongation, and steady state

microfilament polymerization nucleation

rate limiting step; g-actin forms aggregate (stable trimer)

microfilament polymerization elongation

g-actin is rapidly added to actin aggregate (oligomers); (+) end grows quickly; (-) end grows slowly

microfilament polymerization steady state

filament maintains a roughly consistent length; monomers added to (+) end and dissociates at (-) end, results in treadmilling

treadmilling

a dynamic flux of subunits through a microfilament; filament can change length by changing flux via ABPs

capping protein

a ABP that caps the (+) end of f-actin (disabling it); decreases rate of polymerization

types of cell migration

mesenchymal, amoeboid and blebbing

mesenchymal cell migration

fibroblasts; focal adhesions form behind protruding lamellipodia that connect to contractile stress fibers, bracing the cell against eh surface across which it is migrating

amoeboid cell migration

neutrophils and amoeba; a 3D pseudopod is formed by explosive actin polymerization at the leading edge, cells maintain traction despite surface adhesion reduction, enables rapid cell movement

blebbing cell migration

some embryonic cells; a bleb is formed at the leading edge by the plasma membrane detaching from the surface and pushed out by hydrostatic pressure