NBME 24 Vincristine (NBME Answers)

NBME 24 Answers ↦

nbme24/Block 2/Question#46 (24.4 difficulty score)
In a study of drug action on neoplastic cells ...
Vincristine🔍,📺
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+4
submitted by madojo(182),

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As etiodnmne lyaedra, het llce is sukct ni aeteshpma adn nacnto ogrunde het rinpeoteas aasenph.a M ylecc rtrsae si oaiaecssdt twih vriiestnnic adn hhcwi the oiicmtt speilnd which si what atsrseaep hte oomesocrhsm is not .imorgnf

suckitnbme The funny thing is that the image seems to show that the spindle did in fact form. +13

spaceboy98 EXACTLY They showed the mitotic spindle is formed, so paclitaxel would be ok, but for vincristine, the damn thing would not even form +5

-4
submitted by m-ice(346),

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itiiensrcnV si a maohetiprcchuete udrg atth asbeiisztl uomicbsreltu dan tvesenpr ethm fmor .bginlssdsimae Teh clel ni het iceuptr si ksctu in h,pneaasa hwti utosriuclbem aatdcthe ot tsi ecosso,momrh aunelb ot llup hmte arpta aebcesu ti otcnan bssadielmes tis .betsucruoilm

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. +15

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" +

-5
submitted by daddyyikes(1),

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ti wsaz eth het shietsitt oqsiteun atth i evha veer eard ni ym iernte ilfe rve!e