11.12-11.16 Flashcards
what must all motor proteins be able to do?
- bind ATP, hydrolyze it, and undergo a very large conformational change
- bind and let go of surface
2 possible mechanisms of bidirectional movement
- inchworm
- head-over-head
which bidirectional movement mechanism is more likely?
head-over-head
should one head always be attached to microtubule?
- for kinesin yes
- for motors in cilia and flagella: not always
length of steps taken by kinesin and dynein
8 nm
length of single tubulin heterodimer
8 nm
why do motors in cilia and flagella not always need one head bound to micro tubule
so other motors can generate force on same microtubule
for organelles that move bidirectionally, how many dif motors are they bound to?
2
- one set of motors turned off while other is active
2 mechanisms of generating bidirectional movement
- tug of water between motors
- coordination of motor activity
binding cargo to the correct motor is mediated by what?
motor’s tail domain
for kinesin, are the motor or tail domains more similar
motor - tail different to allow binding to proper cargo
does the tail domain bind directly or indirectly to cargo
indirectly - needs adaptor proteins
adaptor AP-1
- links cytoplasmic domain of M6P receptor to tail of kinesin
- links clathrin to regions of TGN where vesicles bud
adaptor AP-1 links the cytoplasmic domain of the M6P receptor to what?
tail of kinesin
what does the dynactin complex link
cytoplasmic dynein to membranes
dyanctin complex composition
7 polypeptides and a short filament composed of Arp1 (similar to actin)
what does Arp1 link
dynein to spectrin
how is spectrin attached to cytoplasmic face of vesicle
ankyrin
are spectrin and ankyrin IMPs or PMPs
PMPs
what is an important property of highly shaped and specialized cell types?
asymmetry
what is movement, dynamic instability, and asymmetry often in conjunction with
actin and intermediate filaments
what happens when growth cones of two cells encounter each other
react to contact signal by extending microtubules to point of contact
why must orientation of spindle during cell division be carefully chosen/
so daughter cells have required orientation - maintain plane of tissue layer
what helps move spindle to correct orientation during epithelial cell division?
dynein
what helps move spindle to correct orientation during yeast budding?
dynein
microtubules also function as what?
cytoskeletal directors - where actin should assemble and contract
microtubules and actin seem to interact through what?
linkers like MAPs and motor proteins
MAP2c
binds to both microtubules and actin in neurons to form and send out long projections
what can linking microtubules to actin filaments also accomplish?
guiding growing microtubules to specific sites in cell
true or false: actin filaments and microtubules must always be physically connected to work together
false - can really signals via signaling pathways, and respond to events from outside or inside the cell
what does signaling between microtubules and actin filaments often involve
G proteins
Rac1
G protein involved with microtubules and actin filaments
steps of Rac1
- microtubule grows/polymerizes
- Rac 1 activated
- stimulates acting filament growth and lamellipodia formation
- reduces effect of Oncoprotein 18 (destabilizer)
composition of cilia and flagella
long bundle of microtubules surrounded by extension of plasma membrane
cilia and flagella of unicellular eukaryotes or sperm
movement
types of unicellular eukaryotes with flagella
- Trypanosoma
- Euglena
- Balantidium
cilia covering apical domains of some epithelial cells
- clearing mucus and debris from respiratory tract
- transporting eggs from ovary to uterus
- circulating cerebrospinal fluid
difference between cilia and flagella
cilia shorter and more numerous
how does each cilia/flagella generate force
- power stroke: bending near base
- recovery stroke: propagates bend from base to tip
true or false: flagella continue to beat if removed from cell, even if plasma membrane is removed
true - just need ATP
core of cilia/flagella
axoneme
how many dif polypeptides in axoneme
at least 250
arrangement of microtubules in motile cilia/flagella
9 + 2
are the plus ends at the tips or base of cilia/flagella
- plus ends at tips
- minus ends at base
nexin
protein responsible for connecting adjacent doublet microtubules around circumference of axoneme
radial spokes and spokeheads
connect doublet microtubules to central pair of microtubules
some of radial spokes and spoke heads are what?
kinases and phosphates that are used in signal network
axonemal dyneins connect what?
adjacent doublet microtubules to generate force within axoneme
number of dif polypeptides of radial spokes and spokeheads
about 17
activity of axonemal dyneins during beating motion
dynein active only with small region - activated sequentially
what regulates the axonemal dyneins
central pair microtubules and radial spokes
when central pair microtubules rotate rapidly, what happens?
transmit signals to radial spokes and regulate dynein activity through kinases and phosphatases
true or false: a flagellum isn’t function during regeneration
false
how are axonemal components transported to the tip or base during flagellar reassembly
intraflagellar transport
what is intraflagellar transport to the tip powered by
kinesin
what is intraflagellar transport to the cell body powered by
cytoplasmic dynein (and C-terminal motor domain kinesin?)
where are nonmotile/primary cilia found
on nearly all vertebrate cells
how many primary cilia do cells typically have
one
axoneme structure of nonmotile cilia
9+0
- lacks central pair of microtubules
ex. of specialized domain on primary cilium
rod and cone cells
what is the tip of the cilium expanded into for rod and cone cells
outer segment
what does outer segment contain
stacks of membrane disks filled with rhodopsin (photoreceptor protein)
what does IFT-type transport do in rod and cone cells
moves membrane vesicles containing rhodopsin from cell body to outer segment
