NBME Answers : pipter's page

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+0 (nbme22#35)

Does anyone have any specific idea on the mechanism of the p53 mutation question regarding the TATA box (the one with the single amino acid conversion and the different hydrogen bonding)?

I chose the decreased binding of RNA polymerase on the TATA sequence of genes that inhibit cell division based solely on the fact that p53 is a tumor suppressor (aka mutated p53->less inhibition of division->multiple divisions).

joha961 From a random paper I found, “Arguably p53’s most important function is to act as a transcription factor that directly regulates perhaps several hundred of the cell’s RNA polymerase II (RNAP II)-transcribed genes.” So normally it increases RNA pol binding; a mutation would decrease it.

estsosa The TATA box is part of the promoter region site where RNA polymerase II and other transcription factors bind to DNA. A defect would therefore decrease binding of RNA polymerase.

mnemonia Also you can reason it out (I got this wrong because you have to be really meticulous) since we know that loss of p53 = cancer. Cancer = want more cell division = don’t want inhibitory gene = less transcription of said gene.

Subcomments ...

submitted by medstudied(1),

Can someone please explain why the answer to this is injury to the posterior cord rather than the radial nerve?

pipter because raising the arm above the shoulder suggests abduction which would mean the axillary nerve is also involved. the lesion would be more proximal. +3

kchakhabar I thought "up to the shoulder" is done by deltoid muscle (aka axillary nerve) and above is done by trapezius. +3

forerofore as far as i can find, abduction ranges of motion, per first aid are: 0-15° = supraspinatus 15-90° = Deltoid 90° = trapezius 100° (over the head) = serratus anterior in this question, they are directly telling you its not the serratus (long thoracic), because no option compromises it. Also, trapezius is innervated by cranial nerve XI, which is not a part of the brachial plexus, so, even though its worded weirdly, you can assume they are talking about deltoid disfunction. so deltoid disfunction (axillary) + radial disfunction = posterior cord +

submitted by natuwalrien(0),

meningiomas count as enhancing lesions? (this comment needs to be more than 50 characters apparently.)

goldenwakosu I think it’s because meningiomas are able to calcify (aka sometimes they have psamomma bodies). I got this question wrong too but I totally did not completely register that the tumor was in the dura (interhemispheric fissure + central sulcus). Hope that helps! +

pipter the only reason I got this right was because they described the tumour as being near the falx cerebri. +1

fcambridge Other hints include being described as round and seen in a female. Both indicative of Meningioma +2

niboonsh also meningiomas typically present with seizures or focal neurological signs +