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Retired NBME 16 Answers

nbme16/Block 4/Question#13 (reveal difficulty score)
A 4-month-old boy is diagnosed with a rare ...
Dilated rough endoplasmic reticulum ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: biochem repeat

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submitted by โˆ—soccerfan23(7)
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COPII = RER to Golgi

COPI = Golgi to RER

HINT: 2 steps forward, 1 step back

If the COPII protein is mutated, then the vesicles and their contents build-up in the RER. Hence, the right answer is dilated RER.

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cheesetouch  FA18 COP II p 47 +



 +3  upvote downvote
submitted by โˆ—pranspach(6)
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*Dilated rER. its not i cell disease. it is a mutation in COP2. Massively dilated RER is an ultrastructural indication of improper processing associated with a disorder where a mutation prevents proper folding and extrusion of protein products.

*dilated RER (C) - reason is that they are asking if stuff not going to golgi what will happen? they are saying trafficking protein broken which sends stuff to golgi. normally whenever a protein is made in RER, it goes down to golgi for packaging. so if its not going to right place it will accumulate in RER and cause dilation of RER.

Cranioโ€“lenticuloโ€“sutural dysplasia the disease causes a significant dilation of the endoplasmic reticulum in fibroblasts of the host Due to the distension of the endoplasmic reticulum, export of proteins (such as collagen) from the cell is disrupted.

The production of SEC23A protein is involved in the pathway of exporting collagen (the COPII pathway) Decreased collagen in CLSD-affected individuals contributes to improper bone formation, because collagen is a major protein in the extracellular matrix and contributes to its proper mineralization in bones

** I copied this from some random memorang on google. I have no clue where s/he got this info from. The first two paragraphs are really all I bothered getting to understand. FWIW COPI and COPII are in FA, but none of this other stuff really is.

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sexymexican888  Also its not I-Cell disease bc if it were the lysosomal enzymes would be in the cytoplasm/serum and it would be all sorts of them and this is a defect in tagging of lysosomal enzymes from rough ER so they can be re-directed to lysosome so when this tagging is defective they just linger in the cytosol/serum so they wouldn't dilate the rough ER +



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