2. cytoskeleton

Question 1

Diameter of microtubules

Answer 1

25nm

Question 2

Why do microtubules usually grow at the plus end?

Answer 2

alpha beta tubulin dimers only form polymers above the critical concentration
critical concentration is lower for addition of polymers at plus end than minus end

Question 3

Why is the minus end always in D form?

Answer 3

Because GTP hydrolysis to GDP is much faster than polymerisation at the minus end

Question 4

In which case is the minus end free to undergo disassembly whilst the plus end polymerises?

Answer 4

Mitosis

Occurs in vitro when Cc(t) < C < Cc(d)

Question 5

What does taxol do?

Answer 5

Stabilises microtubules.

Blocks mitosis but does not have any other effects on microtubule function.

Question 6

How do colchecine and colcemid work?

Answer 6

Microtubule instability - binds to tubulin dimer and prevents polymerisation

Question 7

Outline the stages of dynamic instability

Answer 7

Assembly, catastophe, disassembly, rescue, assembly

Question 8

Describe dynamic instability

Answer 8

Rapid growth with GTP capped plus end
Accidental loss of GTP cap (catastrophe)
Rapid shrinkage
Regain of GTP cap (rescue)
Rapid growth with GTP capped end

Question 9

What does microtubule flux in mitosis aid?

Answer 9

establishment of chromosome bi-orientation and the speed at which sister chromatids separate at anaphase

Question 10

3 different microtubules which make up the bi-polar spindle in interphase and what they link to

Answer 10

Astral MTs - link spindle pole to cell cortex
Kinetochore MTs- connect the spindle poles to the chromosome at the kinetochore
Interpolar MTs - MTs inter-digitate at the centre of the spindle