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  1. When is colchicine added to dividing cells for karyotype studies?

I know that colchicine inhibits polymerization of microtubules.

2 So, why should it stop the cell cycle at metaphase when microtubules have already assembled and the next step(anaphase) requires depolymerization rather than polymerization ?

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colchicine is used to synchronize the cells.. so whenever you add it, the cells will eventually be arrested at metaphase. –  WYSIWYG Dec 21 '13 at 6:59
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1 Answer 1

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Colchicine inhibits the formation of the microtubules by binding to tubilin and rendering it unavailable for the polymerization. Thats why the cells get arrested in the metaphase and can not go on further in the cell cycle and divide. For chromosome studies this is very useful since this is the phase where the chromatin is most condensed and can be viewed best. It inhibits the positive side producing the microtubules to prevent it from moving to the negative side, in cell division.

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I would like to point out that copying from wikipedia without mentioning it as a source is not allowed here. –  biogirl Dec 21 '13 at 10:18
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Sorry, but I haven't looked up this in Wikipedia. Since I have done this stuff myself in the lab I know the background. But I can remove the answer. –  Chris Dec 21 '13 at 10:23
    
In fact I should say sorry because I thought that I had read that exact lines on wikipedia. I looked it up and you say the same thing but not in the same exact words. I really am sorry , I should not have written the comment without confirming. –  biogirl Dec 21 '13 at 10:49
    
Fine for me, such things happen. –  Chris Dec 21 '13 at 10:50
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@biogirl there is a cell cycle checkpoint for the full formation of the mitotic spindle, and a cell poisoned by colchicine will never pass this checkpoint, hence it will never progress to anaphase. –  Roberto Dec 21 '13 at 18:07
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