1. You are curious about the dynamic instability of microtubules and decide to j
ID: 89250 • Letter: 1
Question
1. 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 very fine laser beam that 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 you then severed the microtubules in the middle with a laser beam?
Explanation / Answer
Microtubules assemble by polymerization of -tubulin dimers. A microtubule can oscillate between growing and shortening phases. Microtubules are polar structures with two distinct ends: a fast-growing plus end and a slow-growing minus end.
A. Severing a microtubule in middle (as mentioned in the question) will create new “plus ends “ and “minus ends”. There is greater tendency of microtubule to grow at the plus end by adding GTP-carrying subunits to the plus end, where -tubulin is exposed. However, over some time GTP is hydrolysed, which leaves only a cap of GTP-carrying subunits at the newly created plus end along with the remainder of the tubulin filament containing GDP-carrying subunits. Thus, a plus end that contains GDP-carrying subunits is created. Since the GDP carrying subunits are less tightly bound that that of GTP carrying subunits, the GDP carrying subunits eventually peel away from each other. This leads to depolymerisation of the microtubule leading to shrinkage og microtubule.
Thus, when severed at middle, the newly exposed microtubule plus ends will shrink
B. Now, if non-hydrolysable analogue of GTP containing microtubule is severed with a laser, the newly exposed plus end would contain GTP-carrying subunits. This GTP would NOT hydrolyse to GDP carrying subunit and the microtubule would continue to grow.
Thus, when severed at middle, the newly exposed microtubule plus ends with non-hydrolysable GTP analogue will continue to grow.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.