Cytoskeleton I Flashcards
What form the microvilli?
actin microfilaments
Besides forming microvilli on the apical surface of epithelium what is a major job of actin filaments?
Maintaining cell-cell junctions
What type of filaments extend from the nuclear envelope to the periphery of the cell?
intermediate filaments
T or F: intermediate filaments are very important in maintaining integrity of epithelial cells and muscle cells.
T
What filaments originate in a perinuclear fashion and extend to the periphery of the cell?
Mictotubules
Explain the structure of the microtubule?
alpha and beta dimers combine at ± end to make 13 protofilaments that join to make a hollow tube
T or F: in vitro tubulin can be placed into a tube and when it reaches a certain threshold concentration it polymerizes from positive and negative ends.
True - but growth at the + end proceeds much faster
What is always present in cells to induce microtubule formation?
some type of organizing center (site of nucleation)
Why are nucleation sites needed in vivo?
Because cellular concentrations of tubulin are not high enough to induce spontaneous microtubule formation
What part of the microtubule always inserts in the nucleation site and where on the nucleation site does it insert?
Negative (alpha) side of the tubule enters the gamma tubulin ring complexes on the centriole
T or F: in the absence of any other chemicals as well as in the cellular environment, tubulin will sponaneously assemble and disassemble at the - end?
False, it will assemble and disassemble at the + end
What happens in a growing microtubule?
- tubulin with bound GTP add to the end of the microtubule
- addition of dimers proceeds faster than GTP hydrolysis
- creates a GTP cap
What happens in a shrinking microtubule?
- Protofilaments containing GDP tubulin peel away from the microtubule wall
- GDP tubulin is released to the cytosol
T or F: in the absence of any stimulation tubulin will undergo dynamic instability
True
What family of motor proteins moves toward the positive end of microtubules?
Kinesins
What family of motor proteins moves to the minus end of microtubules?
Dyenins
What is the movement of globular heads in both motor proteins dependent on?
ATP
What is the determining factor for what type of cargo can be transported b motor proteins?
Their tale
What situation garuntees and in tact microtubule?
GTP bound tubulin binding, exceeds the rate of tubulin hydrolysis
T or F: bidirectional vesicles contain both dyeinin and kinesin?
T
What feature of kinesin and dyeinin insures that they won’t fall off the microtubule track?
- They have processive movement driven by ATP hydrolysis
- They always have one globular domain in contact with the MT
What controls expansion and contraction of the ER?
Microtubules
ER follows them
Explain the movement and motor proteins used in transport of proteins out of the ER, into the golgi and out of the cell
Kinesin - moves protein transport vesicle to ER exit site
Dynein - pulls vesicle into the Golgi
Kinesin - pushes the vesicles out of the golgi and out of the cell
How does the golgi maintain its perinuclear position?
Dyneins
