tubulin Flashcards
(30 cards)
what is the purpose of the cytoskeleton?
maintains shape, organization, and provides support for internal and external movement
what are the three elements of cytoskeletel filaments?
microfilaments, microtubules, and intermediate filaments
what are microtubules made of?
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)
what are some parts of the microtubule and their functions?
helical lattice - stiff and hard to bend
orientation of subunits - polarity (+ end grows and shrinks faster)
how does microtubule growth occur?
rapidly, by adding tubulin dimers at the ends
what is microtubule nucleation?
the process where several tubulin molecules interact to form microtubule seed
what is dynamic instability?
process where individual microbubbles alternate between growing and shrinking
what does GTP-tubulin do?
is added to + end of protofilament and causes the end to grow in linear conformation that assembles into the cylindrical wall of microtubule
what is the a catastrophe and rescue?
catastrophe - change from growth to shrinkage
rescue - change from shrinkage to growt
what does hydrolysis of GTP do to protofilaments?
after assemlby it changes the conformation a=of subunits and forces the protofilament into curved shape (bad)
what does nucleation depend on?
the y-tubulin ring complex
where are microtubules generally nucleated?
from the MTOC (microtubule organizing center) where y-tubulin is most enriched
what is the centrosome?
a single, well-defined MTOC that most animals possess
what are centrosomes composed of?
two centrioles and a dense mass of protein (pericentriolar material)
what are MAPs?
microtubule-associated proteins - bind and stabilize microtubules
what sets spacing of microtubule bundles?
Map2 and Tau (mutations cause neurodegenerativea diseases)
what are kinesins?
a tetramer protein that serve as motors that move towards + ends of microtubules
what is kinesin made of?
two heavy and two light chains, has a head that splits ATP for energy (motion) and a tail that is cargo-binding
describe the movement of kinesin?
long-range, one head is always attached to microtubule, takes progressive steps
what family does kinesin belong to?
a large protein superfamily (motor domain of heavy chain is common element
what does kinesin-13 do?
induces depolymerization uniquely from both ends of microtubule
what does kinesin-14 do?
moves from microtubule + ends towards - ends
tail can bind microtubules (organizing)
what is dynein?
another microtubule motor protein that is bigger and more complex than kinesin?
what is dynein made of?
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
