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NBME 22 Answers

nbme22/Block 2/Question#22

A 35-year-old man comes to the physician because of ...

Adenylyl cyclase

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 +5  upvote downvote
submitted by hayayah(349),

Growth hormone releasing hormone acts via G-coupled receptors. G coupled receptors need GTP to become activated and GTPase to become inactivated.

No GTP-ase --> chronically active growth hormone releasing hormone receptor --> constant activation of adenylyl cyclase / cAMP pathway and release of growth hormone.

mcl  This figure is useful https://ai2-s2-public.s3.amazonaws.com/figures/2017-08-08/a025a0e224d366e987bc15edd0f7764ef5611e0d/4-Figure3-1.png +  
mcl  [link](https://ai2-s2-public.s3.amazonaws.com/figures/2017-08-08/a025a0e224d366e987bc15edd0f7764ef5611e0d/4-Figure3-1.png) +  
meningitis  How did you knkow it was GHRH and not GH perse? +1  
meningitis  nevermind; I just read down below. Thank you +  




 +1  upvote downvote
submitted by goldenwakosu(2),

Why is the answer adenylyl cyclase? I looked in FA and I saw that GH uses the JAK2/STAT pathway and that IGF-1 uses the MAP Kinase pathway. Not sure how adenylyl cyclase plays into this.

pug_sheen  I think they are talking about the GHRH receptor on somatotrophs, which works through the cAMP pathway. +  
staygoodpupper  I don’t know how it relates to GH/IGF-1 in particular, but the question said there was a mutation in the alpha subunit of Gs, which activates adenylyl cyclase. +1  
kash1f  I agree the patient does have Acromegaly, but in the question it talked about how the patient had a mutation that prevented the GTPase activity of Gas. So Gs would be overactive --> excess adenylyl cyclase +2  
hyperfukus  ugh i was so excited too bc i thought i remembered jak stat epicfail +