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?
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