7. You are curious about the dynamic instability of microtubules and decide to j

Question

7. You are curious about the dynamic instability of microtubules and decide to join a lab that works on microtubule polymerization. The people in the lab help you grow some microtubules in culture using conditions that allow you to watch individual microtubules under a microscope. You can see the microtubules growing and shrinking, as you expect. The professor who runs the lab gets in a new piece of equipment, a laser beam that is very fine and can be used to sever microtubules. She is very excited and wants to sever growing microtubules at their middle, using the laser beam.
A. Do you predict that the newly exposed microtubule plus ends will grow or shrink? Explain your answer.
B. What do you expect would happen to the newly exposed plus ends if you were to grow the microtubules in the presence of an analog of GTP that cannot be hydrolyzed and then severed the microtubules in the middle using a laser beam?
Hard one – try it.

Explanation / Answer

A. Do you predict that the newly exposed microtubule plus ends will grow or shrink? Explain your answer.

Answer: shrink

Reason:

Microtubules are made of single tubulin protein and it has a dimer i.e. alpha-tubulin & beta-tubulin. These microtubules are going to grow unequally in which, plus end is going to grow faster whereas minus end is going to grow slower. The alpha- tubulin and -tubulin are going to bind with GTP to promote polymerization. The GTP is hydrolyzed here; therefore, if you sever growing microtubules in the middle is leading to formation of plus ends, which have more & more GDP-carrying components finally causing depolymerization due to low ability of GDP binding to GTP-carrying units

B. What do you expect would happen to the newly exposed plus ends if you were to grow the microtubules in the presence of an analog of GTP that cannot be hydrolyzed and then severed the microtubules in the middle using a laser beam?

Answer:

The polymerization of microtubules in the non-hydrolyzable analogue of GTP is followed by laser beam treatment would result in more growth due to exposed and ends with GTP

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