2) In class we looked at one modern method for examining microtubule dynamics in

Question

2) In class we looked at one modern method for examining microtubule dynamics in vivo, which is to use Microtubule end binding proteins like EBI, a protein that binds to the GTP-bound tubulin filaments. a. [4pts) Based on the model of Dynamic Instability, if you watched the mitrotubules in a cell in GO over time using a red fluorescent version of tubulin, and a green fluorescent version of EBI what would you expect to see? b. (4pts) If this particular cell had a lot of microtubule treadmilling rather then just dynamic instability how would your answer above change? c. (4pts) Regardless of the dynamics of your microtubules, if you added a drug that inhibited the activity of kinesin, the plus-end directed microtubule motor protein, what types of effects might you expect to see in a secretory cell in GO?

Explanation / Answer

a) Dynamic instability of microtubules allows them to grow at their + ends and disassemble at their - ends. But based on the rate of assembly and disassembly the growing or shrinking can be carried. In cells in G0 stage no requirmnt of central spindle, so the only cytoskeletal microtubuls present. If tubulin proteins are stained with red fluorescence and EB1 protein with green fluorescence then the red EB1 protein attachment to the + end of green polymerised tubule can be observed. EB1 is a plus-end tracking protein which tract the tubulin monomers to growing edge, it also binds to other +end tracking proteins. So the growing of microtubule at the + end could be observed by this experiment.

b) In treadmilling of microtubules, the shrinking and growing occur at the same time. The fluorescently stained microtubules and EB1 proteins help visualise the growing/ addition of microtubules accompanied by EB1 proteins at + end and shrinking or dissociation of tubulin monomers at - end.

c) After addition of drug which inhibit the kinesin protein, the kinesin cannot carry any protein towards the + end. So the EB1 or tubulin monomers are also could not go to their + end/ growing end. As a result, the growing of microtubules stops. No secretory cell could carry its secretory products to the periphery on microtubules, so the secretory cell cannot secrete their products out of the cell due to inhibition of cargo transport by kinesin

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