NBME 22 Answers : Block 2 : #22 = A 35-year-old man comes to the physician because of ...

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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

+4 upvote downvote
submitted by hayayah(422),

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? +4

meningitis nevermind; I just read down below. Thank you +1

+0 upvote downvote
submitted by goldenwakosu(1),

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. +2

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 +5

hyperfukus ugh i was so excited too bc i thought i remembered jak stat epicfail +

+0 upvote downvote
submitted by osgoodschlatter10(0),

The receptor in question is a G protein receptor on the pituitary mass. This would be the GHRH receptor. The GH receptor will be present downstream so that GH released from the pituitary can bind to it (these are JAK/STAT receptors). GHRH receptors are G¬s receptors. These receptors are bound at the alpha-subunit to GDP in the inactive state. When GHRH binds they activated when GTP attaches to the alpha-subunit instead. And thereby promotoes adenyl cyclase activity. GTPase is responsible to cleave this GTP from the alpha subunit to switch of the receptoe. Therefor a lack of GTPase activity will render he Gs receptor in a prolonged on state  Increased activity of Adenyl Cyclase.