Flashcards in Cytoskeleton (microtubules) Deck (51):
What is the major goal of microtubules?
What is the microtubule function?
What is cytoplasmic scaffolding?
machinery to move organelles within cells and to form mitotic spindle
How does microtubules move the cell?
they form cilia and flagella
What are the proteins that make up microtubules?
What is the makeup of alpha and beta tubulin in cells?
2.5% of all protein in non neuronal cells
What is the structure of microtubules?
long cylindrical hollow structures composed of tubulin subunits arranged in protofilaments
What are the wall of microtubules consist of?
two forms of heterodimers of globular tubulin subunits stacked together
How does the heterodimers form protofilaments?
they line up head to tail to form protofilaments
protofilaments show structural polarity
How many protofilaments form the wall of the tube?
Does the final MT show structural polarity?
yes because all protofilaments line up in the same direction
What is on each end of the MT?
a plus end
a minus end
each end is functionally and structurally distinct, not a charge
Which end polymerize/depolymerize fastest?
Which end polymerize/depolymerize slower?
in vivi minus stabilized by other proteins and dont depolymerize
What is structural polarity important for in MTs?
polymerization and disassembly
What type of protein is tubulin?
a GTP binding protein
Which Tubilin is bound to GTP?
the tubulin in the middle of the dimer is always bound to GTP and cannot hydrolyze or exchange
When does the GTP bound to a tubulin hydrolyze?
after the dimer attaches to a growing MT
When does a tubulin dimer have a high affinity for other GTP tubulin and the plus end of the MT?
When it is bound to GTP
When does tubulin has a low affinity other tubulins and MT?
when it is bound with GDP
What is a GDP bound tubulin in the middle of the MT strand held in place by?
lateral interactions with the rest of the MT
What is the lag phase of MTs?
self aggregation of tubulin dimers. the growth is slow. because small dimers are just as likely to fall apart.
What is the elongation phase (growth phase)?
when a oligomer forms and now is stable and growth proceeds very rapidly
When does rapid growth continue?
when the rate of addition of subunit removal is equal to subunit addition
Why doe the rate of addition slows down?
because free tubulin dimers is limiting so the rate of addition slows while the rate of removal remains the same
What does MTs start from in vivo?
initial nucleation ring
When does self aggregation proceed at a faster rate in vivo?
presence of a nucleus - a basis for developmental growth
Where are the nucleating proteins found?
at the minus end of the MT
What is the nucleation ring complex composed of ?
gamma tubulin and accessory proteins
How many tubulin monomers form the nucleation ring?
How many tubulin rings give rise to a MT?
Where is the nucleation ring located on the MT?
on the static minus end
growing end is the plus end
How are the protofilaments formed?
domers add on to the ring at the plus end
What is the difference of MT growth in vivo vs in vitro?
Vivo -dimers only add to plus end
Vitro-dimers add to both ends
Both cases plus end is always fastest growth
What determines the function and orientation of a microtubule?
Where in the cell it is formed
What does nucleation allow for?
rapid and location specific growth of a MT
What does nucleation occurs in association with in vivo?
Microtubule organizing centers (MTOC)
What are ring complex (nucleation sites) found in association with?
What are the MTOCs in animal cells?
Where are centrosomes usually located?
near the nucleus
What are centrosomes composed of?
pair of perpendicular centrioles surrounded centrosome matrix(pericentriolar material-PMC)
What are centrioles composed of?
9 short MT triplets and accessory proteins that are formed from variations of individual Mts
What is one triplet composed of?
one complete tubule (w/13 protofilamenst ) connected to two incomplete (<13 protofilament) MTs
Which tubule is the inner most complete tubule?
Which tubule is the incomplete?
B and C tubule
Can MT polymerization occur without Centrioles?
centriole function is not known
Do plants and fungal cells have centrioles?
What is the material made of in pericentriolar material?
large number of rings made from tubulin
What does tubulin ring serve as?
a nucleation site for microtubule formation
Where does microtubules originate and radiate from?
in the centrosome
radiate toward the cell periphery