Cytoskeleton (Dynamic instability microtubules) Flashcards Preview

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Flashcards in Cytoskeleton (Dynamic instability microtubules) Deck (21):

Are microtubules dynamic?

they are constantly being built and broken down


What does individual tubules alternate between?

independently alternate between elongation and shortening


What does elongation and shortening allow microtubules to do?

rapidly respond to any situation requiring a change in cytoskeleton


What is the ratio of free tubulin subunits and microtubules in the cell?

they are in equilibrium 50/50


What regulates the total amount of free tubulin subunits and microtubules within the cell?

variations in cell conditions


What favors microtubule growth?

low intracellular calcium


What will inhibit microtubule growth?

calcium concentration greater than 1mM
allows for depolymerization


What is the rapid build up/breakdown of microtubules called?

dynamic instability


What is the dynamic instability of microtubules due to?

GTP binding and hydrolysis activity of tubulin subunit and the resulting change in the tubulin dimers for other dimers


What else is a tubulin?

a GTP binding protein (a GTPase)


What does GTP binding to a tubulin subunit facilitate?

the polymerization of tubulin dimer to the plus end of a growing microtubule


What does adding a GTP tubulin dimer to MT plus end increase?

MT affinity for other GTP tubulin dimers
increases likelihood that another GTP tubulin will bind to the plus end


What is formed at the plus end of MT because of GTP tubulin binding?

a GTP cap


What does the GTP cap refer to?

several rows of tubulin dimers that are still bound to GTP found at the plus end


When is a MT stable and constantly growing?

as long as there is a GTP cap
GTP cap prevents depolymerization


When will a tubulin subunit hydrolyze its GTP?

after a tubulin dimer has been added to the MT
GDP stays on a tubulin subunit and release PO4


When does the tubulin dimer has low affinity for other subunits?

after it has hydrolyzed GTP to GDP
only can come of at the ends of the microtubule


In vivo does the minus end lose GDP tubulin subunits?

no it is capped of by accessory proteins
GDP dimers only come off the plus end
if at plus end it will come off and initiate depolymerization of MT


When is a tubulin dimer is ready to be used again?

when it is in the cytoplasm it can have its GDP be exchange for GTP


How can switch from polymerization to depolymerization occur?

Spontaneously through cellular signals are through individual microtubules


What happens when concentrations of free GTP tubulin decrease?

1)addition of GTP tubulin at plus end of MT slows
2)allows GTP hydrolysis to catch up to plus end (GTP cap shrinks)
3)MT becomes destabilized as GDP-bound dimers are exposed at plus end
4)inititiates depolymerization (occurs rapidly)

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