Cytoskeleton - Part II Motor PROs (25) Flashcards
how is the movement of vesicles & molecules in the cell controlled?
where MTs are placed - growth & direction is directed by the cell
Regulation of the motors:
Activation
Placement on their paths
Movement along path
MT motor PROs?
kinesin & dynein
microfilament motor PROs?
myosin
kinesin
MT motor PRO, move towards + end of MT
Smallest of motor PROs
Pair of globular ends – generate force (walk)
Stalk & fan shaped tail binds cargo
dynein
MT motor PRO, move towards – end of MT
Ubiquitous eukaryotic motor PRO
2 identical heavy chains which generate force
Variety of intermediate & light chains with diff cargo recognition domains
Cargo is attached by dynactin
myosin
microfilament motor PRO, moves along the actin network
how is movement of kinesin & dynein facilitated?
Kinesin & dynein attach to diff adapter PROs which then attach to diff PROs in membranes (vesicles, PM etc.) to generate movement, capture cargo before movement
what 2 motor PROs are involved in ATP dependent movement?
kinesin & dynein
how is ATP movement done?
ATP binding
ATP hydrolyzing
ADP release
causes a conformational change in the motor domain & alters the orientation of the neck linker
what are the heads in motor PROs responsible for?
attachment & movement
dendrites
neuron receives signal
axons
neuron sends signals
Axon MT orientation
minus end points towards cell body & plus end outwards
what is the movement of motor PROs in neurons?
kinesin moves towards the synapse
dynein moves away from the periphery
Kinesin uses ___ ATP/step
1
Kinesin moves along:
a single protofilament
kinesin move only on ____ & ____ are left in b/w steps
betas
alphas
where does kinesin attach to the vesicle?
integral PRO
how many kinesins are found in human cells
40
how do kinesins bind to larger cargo?
aid of cargo or scaffolding PROs (Rab PROs)
how do kinesin exist in the absence of cargo?
fold over & don’t bind MTs
motor PRO ATP dependent movement (Kinesin & dynein)
Once cargo is bound, only one head with bound ADP binds to the MT
ADP is replaced with ATP on the bound head, causing the neck to pivot
Second head binds
Second head has ADP replaced with ATP & the neck bends
ATP is hydrolyzed to allow the trailing head to release from the MT
what is the effect of ATP hydrolysis in motor PROs?
enables the trailing head to release from the MT
what is the effect of swapping ADP with ATP in motor PROs?
neck will bend enabling the head to move
where was kinesin first isolated?
brain tissue
axonal flow
vesicles are carried along MTs from the centrosome in the cell body to axon endings
what motor PRO is involved in carrying vesicles in axonal flow?
kinesin
Myosin V
takes over transport from vesicles, moves along actin filaments to the PM at the synapse
describe the axon endings
extensive actin cytoskeleton
which MT motor PRO is the biggest?
dynein
what are the 2 ways dynactin is involved with dynein?
dynein looks for dynactin
dynactin can be directly found in the membrane
other times dynactin is the intermediate area where it’s attached to Rab PRO
what are the functions of dynein?
C’some movement in mitosis
Positioning of the Golgi, reassembles Golgi post mitosis
Movement of vesicles & organelles
Axonal retrograde organelle movement
Fibroblasts & endothelial cells move endosomes, lysosomes & Golgi derived vesicles toward the cell center
how are motor PROs involved in changing the colour of skin in certain species?
movement of melanosomes
when kinesins are activated (by having more ATP) - they drag melanosomes outwards & darken the cell
when kinesins are inactivated (by having less ATP) - dynein drag melanosomes inwards lightening the cell & creating a dot
chromatophores
pigment-containing cells
melanosomes
organelles with chromatophores containing dark pigment
cilia vs.flagella
CILIA
Shorter
More numerous
Cell movement is perpendicular to the direction of cilia
FLAGELLA
Longer
Rarely more than 2
Flagella are parallel in the direction of movement
functions of cilia
in multicell organisms, move fluids
cilia clear particulates in lungs
cilia of the oviducts move the egg cell
composition of cilia & flagella
MTs surrounded by a PM
all MTs have + ends at the tips & - ends at the base
axoneme
9+2 array of MTs
9 pairs arranged in the circle & 1 pair in the center
Each doublet or pair has 1 complete MT (A-13 protofilaments) & 1 incomplete MT (B- 10-11 protofilaments) B is fused to A Middle pair aren’t fused, held together by bridges & necks
basal body
the MTOC at the base of the flagellum (looks exactly like a centriole)
how does cilia movement occur?
Dynein arms are anchored to A MT, they attach to B MT neighbour
Dynein molecules undergo a conformational change causing A MT to move slightly towards the base of the B MT. Facilitated by ATP hydrolysis
Dynein releases B MT
Nexin holds MT until dynein reattaches to the base of the B MT
Nexin breaks & cycle repeats or, nexin is stretched & the cilia can bend back
in what motion do cilia move?
Sliding of one axoneme alternates with the sliding of the other
Cilia will bend one way & then the other
Cilia bend & move in a circle, do a full rotation
what hypothesis is currently used to describe how cilia move? & what evidence is there?
dynein arm activity is regulated by the central MT pair & radial spokes
cilia that lack an inner core lacks motion
primary cilium
lack the central pair of MT
1/cell
No locomotor function, act as an antenna
Covered with receptors p/u chemical signals & carry them up & down MTs throughout the cell
Mechanoreceptors: bending of the cilium causes triggers the signal to send
ex of the primary cilium sending signals
Kidney epithelium –> fluid flow causes cilia to bend & opens calcium channels which send signals to the rest of the kidney ducts to regulate the flow
Mechanically gated
Ca2+ induced Ca2+ release
Defects in primary cilium lead to kidney disease
how are motor PROs being used in nanotechnology?
Motor PROs can be fixed to microchips
Will shuttle MTs across the cell’s surface, leads to enhanced detection
MTs can be fused with an antibody which will direct the motion of kinesin, can sort through & concentrate components accurately
Sort through blood samples
