Lecture 6: Cytoskeleton Flashcards
components of cytoskeleton
microfilaments
intermediate filaments
microtubules
compare size of cytoskeleton components
microfilaments = actin = 7nm intermediate = tonofilaments = 8-10nm microtubules = 25nm
actin binds to specific transmembrane proteins
cadherins
monomer of actin
G-actin (globules)
polymer/long chain of actin
F-actin (filamentous)
varieties of actin
3
alpha
beta
gamma
G-actin readily binds with ___ .
ATP
G-actin can bind with __ # of other monomers.
2 others
one on each side
actin filaments display _____ .
polarity
overall structure of microfilaments
double helix of G-actin subunits
F-actin polymerization requires ___ .
ATP
polymerization of actin is a _____ situation, meaning……..?
dynamic situation
meaning it is reversible and constantly in flux
ATP-actin is added at the _______ end.
growing end
barbed end
plus end
ADP-actin is found at the ______ end.
slow end
pointed end
minus end
which end of an actin filament is faster in polymerization?
plus end is 5-10x faster
minus end is more prone to depolymerization
low [G-actin]
depolymerization
mild [G-actin]
dynamic equilibrium
high [G-actin]
net addition
polymerization at both ends
***remember barbed is faster than pointed end
a dynamic equilibrium between adding to the barbed end and removal from the pointed end
treadmilling
associated with mild [G]
results in zero net growth
drugs that effect actin polymerization
Cytochalasins
phalloidin
latrunculins
Cytochalasins
bind to barbed ends
inhibiting growth
phalloidin
bind to actin filaments
prevent depolymerization
latrunculins
bind to g-actin
induce depolymerization of f-actin
molecules that can control treadmilling
cofilin
Arp2/3
phalloidin
latrunculins
spectrin
found RBCs - help maintain their cell shape
binds to cortical cytoskeleton plasma membrane
dystrophin
binds to cortical cytoskeleton to plasma membrane
villin and fimbrin
cross link actin filaments in microvilli
calmodulin and myosin I
cross link actin to plasma membrane in microvilli
alpha actin
cross link stress fibers
connect actin to protein plasma membrane complex
filamin
cross link actin at wide angles to form screen like gels
thymosin
holds G-actin in a reserve pool
preventing polymerization
profilin
binds to G-actin catalyzing ADP into ATP
promotes transfer from thymosin to barbed end
promoting polymerization
Arp2/3
initiates growth of F-action from sides of pre-existing filament
cofilin
depolymerization factor
stimulates removal of ADP G-actin at the pointed end
gelsolin
cuts filaments into pieces and caps barbed end
preventing loss or addition of monomers
gelsolin in Ca presence
fragments F-actin and remains bound to plus end
thin filament width
7nm
intermediate filament width
8-10nm
thick filament width
25nm
intermediate filaments are abundant in cells that are subject to _______ stressors. and provide ____ strength
mechanical stress
tensile strength
intermediate assembly
2 polypeptides form a ….?
coiled dimer
staggered antiparallel arrangement
which is more stable between intermediate and thin filaments
intermediate filaments
intermediate assembly
coiled dimers…..?
dimers arrange in staggered antiparallel to form
—–tetramers
intermediate assembly
tetramers…..?
tetramers assemble end to end forming
—–protofilaments
an intermediate fiber is equal to = ?
8 protofilaments
2 monomers =
2 dimers =
8 tetramer bundles =
parallel dimer
tetramer
protofilament
protofilaments arrange in a rod to form…..?
intermediate filament
diameters of microtubules
outer = 25nm inner = 14nm
microtubules are composed of…..
tubulin dimers
alpha+beta subunits
a slice or single row of tubulin dimers
protofilament
a microtubule is equal to =
13 protofilaments
which are arranged in a circle to form a cylinder with a hollow center
distinguish between the ends of a microtubule
plus=fast growing end
minus = slow growing end
plus end of microtubule
fast growing end
beta subunit bound to GTP
grows rapidly in low [Ca]
tubulin is less stable after ________ because ….?
after polymerization
because GTP has been hydrolyzed to GDP
growth pattern of microtubule
capable of growth and shortening at plus end
high [tubulin–GTP]
dimers will add more rapidly than GTP hydrolysis
result = growth of microtubule
low [tubulin–GTP]
GTP at plus end is hydrolyzed to GDP
result = dimers are lost – shortening of microtubule
tubulin is less stable….
when GTP is hydrolyzed to GDP
or called depolymerization
factors that inhibit microtubule polymerization
Colchicines
Colcemid
vincristine & vinblastine
factor that can stop mitosis at metaphase and bind to tubulin dimers (what does this prevent)
colchicines
prevent microtubule polymerization
anticancer drugs that effect microtubule polymerization
vincristine and vinblastine
drug that can stabilize microtubules
taxol
anticancer drug
binds to microtubules – preventing depolymerization
taxol can prevent microtubule ________ , how does this prevent cancer?
prevent depolymerization
does not allow that depolymerization of mitotic spindles which is required for cell separation
how can stabilizing and destabilizing microtubule drugs both fight cancer?
anything that interferes with microtubules, interferes with mitosis
thus not allowing cells to reproduce
functions of the cytoskeleton
cell mvt
cell support, strength, shapes
cell adherence
microtubule monorail system
microtubule roles in mitosis
kinetochore microtubules
mitotic spindles
cytokinesis
microtubules act as a monorail system for moving _____, but how do we attach these to the microtubules?
for vesicle transport
must utilize motor proteins for attachment
kinesin and dynein
vesicle transport from minus to plus end of a microtubule
kinesin
carries full vesicles to destination
vesicle transport from plus to minus end of a microtubule
dynein
carries empty vesicles back to source
why do microtubule’s require 2 different motor proteins
in vesicle transport each protein only travels one way, it is then carried by the other motor protein back to it’s original starting point
if kinesin and dynein only travel one way, how do they get back to their starting point?
they carry each other
myosin I
1 head
tail binds to cell membrane
head binds to actin
direction of head motion toward the barbed end
myosin II
2 heads
tail binds to myosin II
head binds to actin
direction of head motion toward the plus end
kinesin
2 heads
tail binds to vesicle
head binds to microtubules
direction of head motion toward the plus end
cytoplasmic dynein
2 heads
tail binds to vesicle
head binds to microtubules
direction of head motion toward the minus end (pointed)
inactive myosin II tails
have their light chain tails folded back in loops
close to their heads
active myosin II tails
have their tails stretched straight out
