LEC37: Cytoskeleton Flashcards Preview

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Flashcards in LEC37: Cytoskeleton Deck (39):

cytoskeleton function?

organizes intracellular components and helps cells interact mechanically w/ the environment & promote coordinated movements of cells


filament types of cytoskeleton

intermediate filaments, microtubules, actin 


gross structure of cytoskeleton filaments

monomers, protein subunits, that polymerize into filaments


what do eukaryotic cells have in cytoskeleton

actin, tubulin 

metazoans have IF


IF function?

allows cells to be stretched out 

have high tensile strength


IF structure

IF monomer: elongated and alpha-helical w/ globular N-terminus, globular C-terminal tail 

forms a dimer that's a coiled coil

dimers associate to form staggered tetramer 

each tetramer forms associates / 7 others, forms filament of 8 tetramers 

IF have NO POLARITY b/c tetramers form head to tail

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where are IF

around NUCLEUS, forms a network toward cell peripher


what do IF interact w/

junction proteins- desmosomes, hemidesmosomes


IF families of proteins?

1) keratin: in epithelial cells, barrier function, hair, nails 

2) desmins/vimentin: mesenchymal and muscle cells 

3) neurofilaments: neurons 

4) lamins: nucleus of every cell


mutations in keratins causes?

disease i.e. epidermolysis bullosa simplex, blistering of skin as a fxn of mechanical stress


what is keratin function?

family of IF 

protects cells, assists in resisting stretching forces 

works b/c IF in cells can stretch & not break 


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how are neurofilaments associated w/ disease?

NF are an IF

amytrophic lateral sclerosis, ALS, Lou Gegrigs disease, aka motor neuron disease 

if NF accumulate abrnoamlly in axon and cell body or motor neurons

overexpression of NF causes similar mouse phenotype


do IF have reversible assembly ability?

only nuclear lamins do 

during cell cycle, a lamin protein is phoshporylated, which is signal for disassembly; after mitosis, reassembles in the nucleus 



result of lamins mutations?

Progeria: disease resulting from premature aging


what are microtubules function

long, hollow tubes; intracellular oganization and intracellular transport 

form the mitotic spindle, cilia, flagella 


where do cellular MT grow from

the centrosome


structure of MT?

grow from a tubulin dimer of a-tubin & b-tubulin; both bind GTP 

MTs form a linear protofilament, which organizes laterall into a tube containing 13 protofilaments


do MT have polarity?


b/c dimers prefer to bind to exposed B-tublin surface, rather than a-tubulin in a protofilament 

B-tubilin: + end; a-tubulin: - end (centrosome end) which binds to structures composed of gamma-tubulin


how does MT growth occur

dynamic instability 

the minus end is stuck in the centrosome; the plus end grows as the beta subunit hydrolyzes GTP to GDP, causing dimer to bind to a MT and tubulin to peel away at the (+) end 


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what destabilizes/stops MT growth?

if there is lots of tubulin dimer bound to the +, cap end of the MT this destabilizes it, GDP tubulin is released into cytosol 

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what prevents MT polymerization?

drugs- colchicine/vinblastine


what prevents MT depolymerization?

taxol, a chemotherapeutics drug 


what forms mitotic spindles?


for chromosome separation during mitosis


what forms axon tracks?


can be up to a meter long 

very stable trakcs, unlike dynamic MT 

ensures there's no instability on the track


what are motor proteins of MT?

kinesins: plus-end directed

dyneins: minus-end directed 

bind to an organelle (i.e. mitochondria), bind on the other end to the MT


how does chromosome separation occur?

MT, mitotic spindle 

MT connects to kientochord, dissolve there, and then rebind; thus pull spindles apart via dynamic instability, during anaphase


what is cilia and flagella structure

have a 9 + 2 array of MTs inside 

facilitates wavelength/beating motion


what propagates flagella movement?

dynein motors, which're bind to MT, form a sliding motion, which translates to a bend, where 1 end of motor stays in 1 plae and other end moves 

smooth, processive fashion of movement from 1 dynein motor to the other



where are cilia found?

used for movement of materials over cells 

respiratory tract, for moving mucus

oviducts, for moving eggs 


actin function?

for movement - of cells by crawling, and in muscle contraction 

in adherens belt 




moving endocytic vesicles 

contractile ring

helps cells divide


actin structure?

monomer protein, G-actin 

has a + and a - end 

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how does cell crawling occur?

actin is concentrated underneath plasma membrane, at cell cortex, in network/meshwork, which gives plasma membrane shape 

actin polymerization at plus end pushes plasma membrane outward in form of sheets, lamellipodia, and spikes, filopodia 

lamellipodia/filopodia attach to a solid surface, drag cell body forward due to actin/myosin contractile bundles 


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what powers bacteria eg listeria movement


powers them to move within cells, into neighboring cells


what extracellular signals can control cell movement?

growth factors, via small GTPases, Rho, Rac, Cdc42 

these activate formation of actin into assemblies such as stress fibers, lamellipodia, filopodia


how does actin tradmilling occur

actin binds & hydrolyzes ATP which allows actin filaments to grow at plus end, shrink at minus end


why can actin form so many different structures in cells

because of many actin binding proteins 

allow actin monomers to form many configurations of proteins


sarcomere structure?

whole unit: sarcomere

thick filament in middle: myosin 

thin filament: actin 

Z disc bisects actin filament 

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myosin II structure, function?

protein that forms filaments w/ protruding head domains that bind directly to actin, stimulate sliding 

this sliding on actin in sarcomere is muscle contraction 

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what activates muscle contraction?

influx of Ca2+ from sarcoplasmic reticulum activates myosin binding to actin filaments, binding and sliding is muscle contraction

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