Cytoskeleton II: Higher Order Structures and Cellular Functions

actin filament dynamics alter cell - and -

shape, movement

- family of monomeric - regulate actin filament dynamics and cell morphology

Rho, GTPases

accessory proteins with - for actin filaments mediate - between filaments to create different structures with varying rigidity or flexibility

two binding sites, cross-linking

contractile stress fibers are - packed parallel bundles complexed by -, found in -

loosely, alpha-actinin, skeletal muscle

non-contractile stress fibers are - packed parallel bundles complexed by -, found in -

tightly, fimbrin, filopodia

actin gel refers to - actin filaments complexed by -

cris-crossed, filamin dimer

actin gel is a major structure in -, helping stabilize actin web formed in -

cell cortex, lamellipodia

filamin forms a long, - linkage between two criss-crossed actin filaments resulting in a -

wishbone-like, viscous 3D actin gel

lamellipodia are - of the PM all along one side of the cell

thin, sheet-like protrusions

formation of - is the first step in cell crawling because it extends and leads cell in the -

lamellipodia, direction of movement

Arp 2 and Arp 3 are actin nucleating proteins that structurally resemble -

actin monomers

active Arp2/Arp3 complex nucleates a - by binding and recruiting several actin monomers, once nucleated, polymerization occurs rapidly from the - end

new actin filament, plus

Arp complex usually remains bound to - ends, serving as a protein cap that - actin filaments

minus, stabilizes

Arp complex can also bind - on an actin filament, creating new -

internally, nucleated branches

the actin web, as a whole, can undergo -, in which the overall size of the web does not - much, but growth at the leading edge and disassembly at the trailing edge create - movement

treadmilling, change, unidrectional

at the leading edge of the treadmilling actin web, Arp2/3 nucleates - and creates a branched actin web, causing -

at the trailing edge of the treadmilling actin web, cofilin mediates - and consequent disassembly of - resulting in the - of actin monomers to the leading edge

new actin filaments, membrane protrusion

severing, ADP-bound filaments, recycling

cell crawling is complex, requiring 4 distinct and coordinated movements

1. extension

2. adhesion

3. translocation

4. de-adhesion

extension/protrusion refers to the actin-web pushing PM - at the leading-edge of the cell to form a protruding -

outwards, lamellipodium

adhesion refers to the cell cortex connecting to the -

extracellular matrix

translocation refers to the cell body being - to catch up to the leading edge, mediated by - powered by -

pulled forward, contractile actin bundles, myosin II

de-adhesion refers to the - of cell cortex from the -

detachment, ECM

MTOC in animal cells and most eukaryotic cells is the -, comprised of

1. pair of -, each made from 27 short MTs packed into a cylindrical bundle

2. rings of - that nucleate the minus end to grow new MTs from the centrosome

3. variety of -

centrosome

centrioles, gamma-tubulin, accessory proteins

centrosome is duplicated during - and form -

S-phase, mitotic spindles

an interphase cell contains a single -, located near the -

cytoplasmic array of - radiate from the centrosome to virtually all regions of the cell

centrosome, nucleus

microtubules

cytosolic microtubule and - contact provide - for the - end of microtubule growth

PM, negative feedback, plus

kinesins are superfamily of proteins that walk along - toward the - end

microtubules, plus

kinesins have neck region between two motor heads to alternately mediate - and - on the microtubule

docked head has -, undocked head has -

docking, undocking

ATP, ADP

how do kinesins work?

1. leading head exchanges ADP for ATP, causing it to be - to the microtubules and for it to -

2. simultaneous - on lagging head + release of - from lagging head allows for it to detach from MT so it can swing forward to be the -

tightly anchored, swing forward, ATP hydrolysis, Pi, leading head

heavy chain tails of kinesin contain a binding site for - or another - and can even carry an entire - along a microtubule

vesicles, microtubule, organelle

dyneins are another family of - proteins that walk towards the - end of microtubules

motor, minus

dyneins are important in - and helps in localization of the -

vesicular trafficking, golgi apparatus

mitosis requires the separation of duplicated chromosomes and division of nuclei, performed by -

the spindle microtubules form from - that migrate to - of the dividing cell

bipolar mitotic microtubule spindles

duplicated chromosomes, opposite poles

cytokinesis is the division of -, performed by the - containing both - and - filaments

contractile ring forms around the - of the cell just beneath the plasma membrane, once contracted, it pulls the membrane - until two daughter cells pinch off

cytoplasm, contractile ring, actin, myosin

equator, inward

what are the green microtubules?

blue microtubules?

purple microtubules?

astral

kinetochore

interpolar

blue? red? green?

blue is the duplicated chromosomes

red is the kinetochores

green is the kinetochore microtubules

alignment of chromosomes at the metaphase plate involves both - and - of chromosomes

plus end - push tips of chromosomes along - microtubules

- of - microtubules at the plus end pulls chromosome at the -

pulling, pushing

kinesins, interpolar

depolymerization, kinetochore, kinetochore

top left line?

top right line?

bottom line?

top left line points to interpolar or astral microtubule

top right line points to plus-end-directed kinesin

bottom line points to kinetochore microtubule

there is a - of - microtubules during anaphase A

shortening, kinetochore

separation of sister chromatids and movement to poles are mediated by - (shortening/lengthening) of - microtubules by - (de/polymerization) at - (minus/plus) ends

shortening, kinetochore, depolymerization, plus

how can microtubule plus ends de-polymerize while attached to the kinetochore?

microtubule collar connects microtubule to the kinetochore, sliding down the microtubule as it shortens

there is a - of - microtubules at anaphase B

lengthening, interpolar

just after sister chromatids detach from each other and begin to separate, the poles themselves begin to move - (together/apart)

apart

separation of poles is mediated by - microtubules

polymerization at - ends of interpolar microtubules in - region

at the overlap region, - will cause the microtubules to slide against each other, pushing the poles -

interpolar

plus, overlap

kinesins, apart

kinesin motor proteins connect interpolar microtubules at overlapping regions, walking towards - (shortening/lengthening) - ends creating the sliding force that helps push the poles -

lengthening, plus, apart

dynein motor proteins anchor - microtubules to the - and when walking toward the - end, it generates - force on the centrosome, pulling the poles -

astral, cell cortex, minus, pulling, apart

actin specific drugs

1. phalloidin

2. cytochalasin

3. swinholide

4. latrunculin

microtubule-specific drugs

1. taxol

2. colchicine

3. vinblastine

4. nocodazole