Cytoskeleton*

Question 1

what are the primary fibers comprising the cytoskeleton?

Answer 1

microfilaments, microtubules and intermediate filaments

Question 2

give the 5 details of the microfilament structure

Answer 2

1. Actin is a globular protein 43-46 kD MW, which binds to ATP.
2. Actin molecules are joined together in a twisted double-strand to form a microfilament.
3. Microfilaments have polarity, with new actin monomers added preferentially to the + end and disassembled at the – end.
4. Microfilaments self-assemble without using energy, but disassembly requires hydrolysis of ATP.
5. Microfilaments are associated with ABPs (actin-binding proteins).

Question 3

name the purpose of the drugs for microfilaments; cytochalasin, phalloidin and blebbistatin

Answer 3

depolymerization, stabilization and inhibition of non-muscle myosin

Question 4

give the 6 details of the microtubule structure

Answer 4

1. Alpha and beta tubulin are roughly 55 and 57 kD MW. They are quite similar.
2. The essential microtubule subunit is a heterodimer of alpha and beta tubulin.
3. In cross-section, a microtubule consists of 13 dimers arranged around a hollow core. In longitudinal section, the rows of dimers are called protofilaments.
4. Microtubules have polarity, with new subunits added preferentially to the + end, and disassembly occurring at the - end. Assembly and disassembly occurs extremely rapidly, in response to Ca++ and temperature
5. Microtubules are capable of self-assembly. Although energy is not required, adding GTP to the ends stabilizes the microtubule.
6. Microtubules are associated with MAPs (microtubule- associated proteins), which tend to stabilize the microtubule structure.

Question 5

MTOC

Answer 5

Microtubule Organizing Center. Microtubules radiate from MTOC near the nucleus

Question 6

Kinesins are what end directed?

Answer 6

Plus end directed. Minus to plus.

Question 7

Dyneins are what end directed?

Answer 7

Minus end directed. Plus to minus.

Question 8

Taxol

Answer 8

stabilizes microtubules. Preventing further assembly or disassembly. Used to treat lung, ovarian, and breast cancer.

Question 9

Antitubulins

Answer 9

destabilize microtubules (colchicine, vinblastine, podophyllin)

Question 10

What are the 5 diseases associated with microtubules?

Answer 10

1 CF
2 Lissencephaly "smooth brain"
3 Polycystic kidney disease
4 Kartagener's syndrome
5 Alzheimer's disease

Question 11

Which structure of cytoskeleton is not essential for survival

Answer 11

intermediate

Question 12

In cell division, what are the two initial steps?

Answer 12

1. Before cytokinesis, the microtubules must depolymerize.
2. Meanwhile, the centrioles replicate in the centrosome (MTOC). The centrosome splits and the two halves move to opposite sides of the cell.

Question 13

What are the 4 steps for the cytoskeleton in cell divison

Answer 13

Depolymerization, aster formation, formation of kinetochore microtubules and cleavage and repolymerization