LEC37: Cytoskeleton Flashcards
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
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
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?
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
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
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
what prevents MT polymerization?
drugs- colchicine/vinblastine
what prevents MT depolymerization?
taxol, a chemotherapeutics drug
what forms mitotic spindles?
MT
for chromosome separation during mitosis
what forms axon tracks?
MT
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
microvilli
filopodia
phagocytosis
moving endocytic vesicles
contractile ring
helps cells divide
actin structure?
monomer protein, G-actin
has a + and a - end
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
what powers bacteria eg listeria movement
actin
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
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
what activates muscle contraction?
influx of Ca2+ from sarcoplasmic reticulum activates myosin binding to actin filaments, binding and sliding is muscle contraction
