microtubules 3 Flashcards
what are the incredible properties for actin and for microtubules?
actin: treadmiling
microtubules: dynamic instability
what is one of the most important function of the microtubules?
longe-range transport
what is longe range transport mediated by?
motor proteins
what are the 2 motor proteins and which direction are they going in?
-kinesin: + direction
-dynein: - direction
which direction do the following things go in:
-secretory vesicle
-lysosomes/late endosomes
-early endosome
-mitochondrion
-endoplasmic reticulum
-pigment granule
- (+)
- (-)
- (+)
- both
- (+)
- both
what carries secretory vesicles?
kinesin
which scientific study allowed us to study intracellular transport
the pigment molecules in xenopus laevis:
-frog is able to change its colour, often related to when its ready to mate
-behavioral change in response to environment
-melanophore cells have molecules called melanosomes moving around
-studying these cells allows us to see that cells are capable of moving things
true or false, intracellular transport is always on?
false, it can be activated or inhibited by signaling molecules
explain how xenopus laevis change their colour?
-they have specialized cells in their skin called melanophores
-inside the melanophores, have molecules called melanosomes
-when high concentration of cAMP, melanosomes are dispersed
-when lows concentration of cAMP, melanosomes aggregate in the middle of the cell
what is the relation between melanosome distribution and colour of the frog?
-dispersed: light colour
-piled in the middle: dark colour
true or false, microtubules are the roadways for the transport of organelles
true (was seen through electro microscopy)
what are the design problems for intracellular transport?
-how can we make a protein walk?
-roads must be directional, as we always have things moving in and out of the cell
-not all roads lead to the same place, so which road do we take (ex in neuron, going either to the axon or the dendrites)
-how do we select the right cargo. want the proteins to grab and carry the right things
what does kinesin do?
motor protein that walks to the microtubule plus end
what type of conversion does a motor protein do?
converts chemical energy into mechanical energy
where does the cargo bind in the kinesin?
tail
whats the motor domain of the kinesin?
head
whats the coiled coil domain of the kinesin?
the stalk
true or false, the light chain of the kinesin is connected to the motor (heavy chain)
false, they are separate molecules
what transports vesicular cargo?
kinesin
what do vesicles have, which helps them bind to kinesin?
kinesin receptor
which molecule can we compare kinesin with? why?
-myosin
-they share a catalytic core that hydrolyzes ATP
-makes us think that there’s a common evolutionary origin. early in history of life, evolution discovered how to make a protein domain that could convert ATP hydrolysis into large scale conformational changes. conformational changes also happen near catalytic site
what is the world’s tiniest biped?
kinesin
true or false, kinesin stays on microtubules forever
false. we see green dot a bit before it falls off (in experiment where microtubules are in red and green is the kinesin). kinesin can only take a finite number of steps before it dissociates
explain the steps for the kinesin walking
1) at first, both motor heads have ADP attached to them
2) one head collides with the microtubule, which makes it release the ADP. it is now bound tightly to the microtubule
3) nucleotide binding pocket doesnt like to be empty, so then ATP comes in and binds
4) when ATP binds, conformational change in the neck linker, which swings the rear motor head forward
5)as rear motor head swings forwrds, it has to lose its ADP, so that it can bind to the microtubule
6) after the new forward head is bound (ADP released), rear head must hydrolyze its ATP, before the front head can recieve ATP
7) ATP binds to front head and cycle restarts
what is the coordination issue with the kinesin walking? how is this fixed?
we want the rear head to hydrolyze ATP before the front head receives ATP, or else kinesin will lose balance and fall off. Also if foot hydrolyzes its ATP and release phosphate before other is bound down, kinesin will fall and dissociate. need to make sure that back head hydrolyzed its ATP, so that its in its loose ADP form, so that when ATP binds to front head, it can swing forward since its loose
how this is fixed: stain receptor
how does the strain receptor work in kinesin?
front foot: strain causes it to not be able to bind to ATP. when strain released (when ATP hydrolyzed to ADP), then it can bind to ATP
back foot: strain forward pulling accelerates rate of ATP hydrolysis
true or false, when the motor head is bound to ADP, it binds tihgtly to microtubules
false, it binds loosely
how many steps does the kinesin take before dissociating? why does it dissociate?
-about 100 steps. errors occur 1 in every 100 steps, which then causes them to dissociate
-it dissociates because ATP hydrolysis reaction happens in the back head too fast, before front foot can anchor down (release its ADP). Now we have 2 ADP bound heads, so they’ll both be loose and kinesin will fall off. Any disruption in coordination will lead to detachment
what is the minus end directed motor protein?
dynein
how many ATPases are in dynein?
6
what is responsible for the forwrd movement in dynein?
rotation of ATPase domains , moves coiled coil domain, which is attached to the cargo
true or false, dynein is part of the kinesin family
false
which part of dynein binds to the microtubule?
the stalk
what do we call the movement of the dynein?
power stroke
how do both the dynein and kinesin allow for the transport of multiple different cargos (recognition)
-kinesin: we have 45 diff kinesins that bind to different things
-dynein: the dynein binds to an adaptor (intermediate between it and the cargo. only one type of dynein, but multiple adaptors, which allows for diversification of transport
what is the function of dynactin?
binds to dynein and helps it recruit adapter proteins
what do dynein motors power the motion of (speciifc example)
-powers the beating of flagella (motion of sperm and chlamydomonas)
how exactly do dyneins give rise to flagellar beat? explain the mechanism
-flagella made of microtubule doublets
-dynein between sets of doublets, and the one that has the stalk on it, the dynein will walk towards its negative end
-microtubules will slide relative to each other, but not freely, cause there are cross linkers between doublets, so there will only be bending
-
how are the different roads in microtubules determined?
-post translational modifications of tubulin marks different microtubule roads
-the c terminal of the tubulin of the microtubule is modified (the tails stick out from the microtubule)
-
true or false, histone tails are more post translationally modified than c terminals
false
what is the c terminal modified by?
enzymes
what is polyglycylation?
G side chain addition to c terminal
what is polyglutamylation?
addition of glutamate to c terminal
what are the post translational modifications of the different regions of the neuron?
