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nbme24/Block 2/Question#46 (21.6 difficulty score)
In a study of drug action on neoplastic cells ...
Vincristine🔍
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 +3 
submitted by madojo(163),
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suckitnbme  The funny thing is that the image seems to show that the spindle did in fact form. +10  
spaceboy98  EXACTLY They showed the mitotic spindle is formed, so paclitaxel would be ok, but for vincristine, the damn thing would not even form +4  



 -4 
submitted by m-ice(326),
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inVcirnseti si a pmtaieetoruchhec rdgu htat szitbislea curesilmotbu adn nstperev mhte romf dsnlg.seisaibm heT ellc ni het icpurte si ctsuk ni nae,pasha hwti blteucmuisor ecaadtht to sti ohrmocmsse,o lbeaun ot llup htme artpa aucebes it ntcnao ssmdbseeail tis mreou.uciblst

vshummy  So I get that by process of elimination cyclophosphamide, cyclosporine, doxorubicin, and 5-fluorouracil are not related to microtubules but vincristine in First Aid 2019 says it prevents microtubule formation, doesn’t stabilize it because the one that stabilizes microtubules is paclitaxel. +  
vshummy  Okay, I realize now- the picture is stuck in metaphase, not anaphase. Both paclitaxel and vincristine stop the cell in metaphase but by two different mechanisms. Vincristine prevents mitotic *spindle* formation while paclitaxel prevents mitotic spindle *breakdown*. Mitotic spindle is needed to pull the chromosomes apart before anaphase begins. +14  
azibird  No, I think you were right to begin with. Without spindle formation the cell should be stuck in prophase (vincristine). Without breakdown it should be stuck in metaphase (paclitaxel). Metaphase is shown here with spindle fully formed, so it should be paclitaxel. +  
sars  I agree with the logic stated above. It could also be that the researchers added Drug X later on in M-phase, so therefore maybe the microtubules aren't even fully formed to fully reach metaphase. I think they're harping on "pick the best answer" +  
sars  I agree with the logic stated above. It could also be that the researchers added Drug X later on in M-phase, so therefore maybe the microtubules aren't even fully formed to fully reach metaphase. I think they're harping on "pick the best answer" +  



 -4 
submitted by daddyyikes(1),
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ti aswz hte het ihtttisse enuiqtos htat i evah eevr erda ni my eneirt life rvee!