Activity: Dynamic Instability of Microtubules Part A What causes catastrophe of

Question

Activity: Dynamic Instability of Microtubules

Part A

What causes catastrophe of the microtubule in vitro?

Part B

What is the role of GTP in microtubule polymerization?

Part C

What would happen in the treadmilling experiment if a non-hydrolyzable analogue of GTP were used?

Part D

What is the difference between the plus and minus ends of the microtubule in in vitro experiments?

Part E

How would the drug taxol affect the in vitro dynamic instability and treadmilling experiments?

the lack of tubulin heterodimers non-motor Microtubule Associated Proteins (MAPs) GTP hydrolysis mutation of the -tubulin

Explanation / Answer

Answer:

Part A: (c) GTP hydrolysis

Explanation:

Dynamic instability results from the biochemical and structural properties of the polymerizing -tubulin subunits and how they interact with the microtubule lattice. Unpolymerized, GTP-bound -tubulin subunits assemble into microtubules, where their GTPase activity is greatly accelerated.

Part B: (d) GTP stabilizes the tip of the microtubule, allowing more monomers to be added.

Explanation:

GTP hydrolysis has been shown to be a key regulator of microtubule polymerization dynamics. Although the exact mechanisms are poorly understood, two opposing models have been proposed to describe how GTP could alter the conformation of -tubulin/-tubulin from the intrinsically ‘bent spring’ shape that resists straightening, to the straight conformation that gives rise to microtubule stability.

Part C: (b) The microtubule would treadmill until the new tubulin, with non-hydrolyzable GTP, reached the minus end, and then it would only extend at the plus end.

Part D: (c) The plus end has a lower critical concentration for tubulin heterodimers.

Explanation:

Critical concentration is the tubulin concentration at which MT assembly is exactly balanced by disassembly. The microtubule assembly in vitro depends on concentration of tubulin dimers, MTs grow when tubulin concentration exceeds the critical concentration & vice versa. The plus end has a lower critical concentration than minus end.

Part E: (c) Taxol would stabilize the microtubules in both experiments, leading to polymerization without catastrophe.

Explanation:

Taxol prevents tubulin subunits from dissociating (blocks mitosis and thus used to treat cancer).

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