LEC37: Cytoskeleton

Question 1

cytoskeleton function?

Answer 1

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

Question 2

filament types of cytoskeleton

Answer 2

intermediate filaments, microtubules, actin

Question 3

gross structure of cytoskeleton filaments

Answer 3

monomers, protein subunits, that polymerize into filaments

Question 4

what do eukaryotic cells have in cytoskeleton

Answer 4

actin, tubulin

metazoans have IF

Question 5

IF function?

Answer 5

allows cells to be stretched out

have high tensile strength

Question 6

IF structure

Answer 6

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

Question 7

where are IF

Answer 7

around NUCLEUS, forms a network toward cell peripher

Question 8

what do IF interact w/

Answer 8

junction proteins- desmosomes, hemidesmosomes

Question 9

IF families of proteins?

Answer 9

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

Question 10

mutations in keratins causes?

Answer 10

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

Question 11

what is keratin function?

Answer 11

family of IF

protects cells, assists in resisting stretching forces

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

Question 12

how are neurofilaments associated w/ disease?

Answer 12

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

Question 13

do IF have reversible assembly ability?

Answer 13

only nuclear lamins do

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

Question 14

result of lamins mutations?

Answer 14

Progeria: disease resulting from premature aging

Question 15

what are microtubules function

Answer 15

long, hollow tubes; intracellular oganization and intracellular transport

form the mitotic spindle, cilia, flagella

Question 16

where do cellular MT grow from

Answer 16

the centrosome

Question 17

structure of MT?

Answer 17

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

Question 18

do MT have polarity?

Answer 18

yes

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

Question 19

how does MT growth occur

Answer 19

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

Question 20

what destabilizes/stops MT growth?

Answer 20

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

Question 21

what prevents MT polymerization?

Answer 21

drugs- colchicine/vinblastine

Question 22

what prevents MT depolymerization?

Answer 22

taxol, a chemotherapeutics drug

Question 23

what forms mitotic spindles?

Answer 23

MT

for chromosome separation during mitosis

Question 24

what forms axon tracks?

Answer 24

MT

can be up to a meter long

very stable trakcs, unlike dynamic MT

ensures there’s no instability on the track

Question 25

what are motor proteins of MT?

Answer 25

kinesins: plus-end directed
dyneins: minus-end directed

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

Question 26

how does chromosome separation occur?

Answer 26

MT, mitotic spindle

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

Question 27

what is cilia and flagella structure

Answer 27

have a 9 + 2 array of MTs inside

facilitates wavelength/beating motion

Question 28

what propagates flagella movement?

Answer 28

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

Question 29

where are cilia found?

Answer 29

used for movement of materials over cells

respiratory tract, for moving mucus

oviducts, for moving eggs

Question 30

actin function?

Answer 30

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

in adherens belt

microvilli

filopodia

phagocytosis

moving endocytic vesicles

contractile ring

helps cells divide

Question 31

actin structure?

Answer 31

monomer protein, G-actin

has a + and a - end

Question 32

how does cell crawling occur?

Answer 32

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

Question 33

what powers bacteria eg listeria movement

Answer 33

actin

powers them to move within cells, into neighboring cells

Question 34

what extracellular signals can control cell movement?

Answer 34

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

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

Question 35

how does actin tradmilling occur

Answer 35

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

Question 36

why can actin form so many different structures in cells

Answer 36

because of many actin binding proteins

allow actin monomers to form many configurations of proteins

Question 37

sarcomere structure?

Answer 37

whole unit: sarcomere

thick filament in middle: myosin

thin filament: actin

Z disc bisects actin filament

Question 38

myosin II structure, function?

Answer 38

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

this sliding on actin in sarcomere is muscle contraction

Question 39

what activates muscle contraction?

Answer 39

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