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nbme24/Block 2/Question#46 (21.5 difficulty score)
In a study of drug action on neoplastic cells ...
Vincristine🔍
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 +3 
submitted by madojo(160),
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rilpCyconso si na utsimoerpapsmnusn htta bcsokl T ellc viciaoattn yb thibinniig 2,LI- so ew onwk httsa not hit.rg ohmadeyChicpspol is na angyiltalk ne.tga oxrbDocniui is an atmrutoni caitnbitoi hatt ngeestrae eerf asalcird and usaesc rsekba ni ADN. lfalri'5ruoouc is esastcoai htiw ryiieinpdm tnys.seish Lveigna ncriinVesit chihw is a pacelnotsi gudr taht srkow on botrusumceli e(thor drsug atht do isht loicnci,che ceaixllt.ap

sA metindnoe lade,ayr hte llec si kcsut ni hematpaes nda nnocat rneudog the oerpaintes e.ahapnas M leccy starer is oaisaectds ihtw vsiniticren dna whcih hte miottic neidslp whchi si thaw aertspeas hte hoosesrmmco is otn grominf.

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(325),
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eininVtcrsi is a chrthetmcpeaeiou udgr hatt issezbital rmebusioutcl adn tsenevpr emth fmro sgdi.mbsnlaesi hTe lcel ni eth tpercui is kcstu ni ,anaepahs twhi tolsueucrimb aeadtcht to its smhromseoc,o nubeal to lplu hmte atrap sueebca it aoncnt smisabeleds sit ceulmouir.tsb

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 szwa eth eth titsisteh oneqisut ttha i hvea vere adre ni ym rienet eifl !rvee