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NBME 22 Answers

nbme22/Block 1/Question#50

A 9-year-old boy is brought to the physician by his ...

Protein structure

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submitted by organicmechanic(1),

Increased sweat and Na+ concentration should point to cystic fibrosis (CF). The problem with CF is not that the gene is being transcribed less, but that the protein that the gene codes for is altered, which leads to the CF channel being degraded due to mis-folding --> less CF receptors on cell surface --> phenotypic CF.

ls3076  why not membrane receptor? +1  
a1913  delF508 is a 3 base pair deletion of phenylalanine at amino acid position 508. Mutation causes impaired post-translational processing of CFTR (improper folding) which rough ER detects. Sends mutant misfolded CFTR to the proteasome for degradation, preventing it from reaching cell surface. So problem is not malfunctioning CFTR channels in the surface; problem is complete absence of CFTR on cell surface (since they keep getting misfolded and sent to proteasome to be trashed). Source of primary problem: error in protein structure +  

 +0  upvote downvote
submitted by a1913(0),

delF508 is a 3 base pair deletion of phenylalanine at amino acid position 508. Mutation causes impaired post-translational processing of CFTR (improper folding) which rough ER detects. Sends mutant misfolded CFTR to the proteasome for degradation, preventing it from reaching cell surface. So problem is not malfunctioning CFTR channels in the surface; problem is complete absence of CFTR on cell surface (since they keep getting misfolded and sent to proteasome to be trashed). Source of primary problem: error in protein structure