tubulin

Question 1

what is the purpose of the cytoskeleton?

Answer 1

maintains shape, organization, and provides support for internal and external movement

Question 2

what are the three elements of cytoskeletel filaments?

Answer 2

microfilaments, microtubules, and intermediate filaments

Question 3

what are microtubules made of?

Answer 3

they are polymers of tubulin (made of alpha and beta tublin), built from 13 parallel protofilaments (composed of tubulin heterodimers stacked head-tail and folded into a tube)

Question 4

what are some parts of the microtubule and their functions?

Answer 4

helical lattice - stiff and hard to bend
orientation of subunits - polarity (+ end grows and shrinks faster)

Question 5

how does microtubule growth occur?

Answer 5

rapidly, by adding tubulin dimers at the ends

Question 6

what is microtubule nucleation?

Answer 6

the process where several tubulin molecules interact to form microtubule seed

Question 7

what is dynamic instability?

Answer 7

process where individual microbubbles alternate between growing and shrinking

Question 8

what does GTP-tubulin do?

Answer 8

is added to + end of protofilament and causes the end to grow in linear conformation that assembles into the cylindrical wall of microtubule

Question 9

what is the a catastrophe and rescue?

Answer 9

catastrophe - change from growth to shrinkage
rescue - change from shrinkage to growt

Question 10

what does hydrolysis of GTP do to protofilaments?

Answer 10

after assemlby it changes the conformation a=of subunits and forces the protofilament into curved shape (bad)

Question 11

what does nucleation depend on?

Answer 11

the y-tubulin ring complex

Question 12

where are microtubules generally nucleated?

Answer 12

from the MTOC (microtubule organizing center) where y-tubulin is most enriched

Question 13

what is the centrosome?

Answer 13

a single, well-defined MTOC that most animals possess

Question 14

what are centrosomes composed of?

Answer 14

two centrioles and a dense mass of protein (pericentriolar material)

Question 15

what are MAPs?

Answer 15

microtubule-associated proteins - bind and stabilize microtubules

Question 16

what sets spacing of microtubule bundles?

Answer 16

Map2 and Tau (mutations cause neurodegenerativea diseases)

Question 17

what are kinesins?

Answer 17

a tetramer protein that serve as motors that move towards + ends of microtubules

Question 18

what is kinesin made of?

Answer 18

two heavy and two light chains, has a head that splits ATP for energy (motion) and a tail that is cargo-binding

Question 19

describe the movement of kinesin?

Answer 19

long-range, one head is always attached to microtubule, takes progressive steps

Question 20

what family does kinesin belong to?

Answer 20

a large protein superfamily (motor domain of heavy chain is common element

Question 21

what does kinesin-13 do?

Answer 21

induces depolymerization uniquely from both ends of microtubule

Question 22

what does kinesin-14 do?

Answer 22

moves from microtubule + ends towards - ends
tail can bind microtubules (organizing)

Question 23

what is dynein?

Answer 23

another microtubule motor protein that is bigger and more complex than kinesin?

Question 24

what is dynein made of?

Answer 24

head is force generation motor
stalk has microtubule binding site at tip
tail is cargo binding
atp changes the conformational structure to dissociate microtubule binding

Question 25

how does dynein move?

Answer 25

in big but irregular steps, towards - end

Question 26

what do microtubule motors do?

Answer 26

move vesicles in secretory pathways

Question 27

what mediates movement of melanosomes?

Answer 27

dynamin and microtubules

Question 28

what does inhibiting kinesin do?

Answer 28

promotes - end transport

Question 29

what are cilia and flagella?

Answer 29

hairlike appendages with bundles of microtubules at their core (axoneme)

Question 30

what does axonemal dynein do?

Answer 30

bends axoneme to move the cilium and flagellum