The function of microtubules depends on their specific spatial organization with

Question

The function of microtubules depends on their specific spatial organization within the cell. How are specific arrangements created, and what determines the formation and disappearance of individual microtubules? To address these questions, investigators have studied the in vivo assembly of áâ-tubulin dimers into microtubules. Below 15 ìM áâ-tubulin, no microtubules are formed; above 15 ìM áâ-tubulin, microtubule readily formed (Fig. A). If centrosomes are added to the solution of tubulin, microtubules begin to form at less than 5 ìM (Fig. B).

A. Why do you think that the concentration at which MT begin to form (the critical concentration) is different in the two experiments?

B.Why do you think that the plot in figure A increases linearly with increasing tubulin concentration above 15 ìM, where the plot in figure B reaches a plateau at about 25 ìM.

Analysis of MT assembly. (A) Mass of MTs assembled in the absence of centrosomes as a function of tubulin concentration. (B) Average number of MTs per centrosome as a function of tubulin concentration. Concentrations refer to ab-tubulin dimers, which are the subunits of assembly.

Explanation / Answer

Microtubules are created and dispersed through the cell by the centrosome. The centrosome is only located in animal cells and it its specific location is in the cytosol, not the nucleous.

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