1. Explain the structural cap model of dynamic instability of microtubules.
2. Phalloidin, a chemical found in poisonous mushrooms, stabilizes microfilament structure. Usually stabilization is considered to be a good thing. Why is it a problem in this case?
Answer 1:
Dynamic instability refers to the transition between rapid shortening and slow growth at the ends of a single microtubule. Microtubules are made up of a dimeric protein called tubulin (alpha and beta-tubulin). A GTP bound tubulin acts as a protective cap and prevents disassembly of the microtubule. When this GTP is hydrolyzed to GDP, rapid depolymerization of the microtubule takes place. This is called catastrophe, and addition of another GTP bound tubulin provides a cap, which is called rescue.
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