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NBME 18 Answers

nbme18/Block 1/Question#1 (11.9 difficulty score)
During a study of the regulation of ...
F (cell diagram)🔍
tags: cell_transport cell_trafficking cell_bio 

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 +6 
submitted by azibird(158),

This is the most poorly drawn cell diagram. I see zero ribosomes, so I figured F was the smooth endoplasmic reticulum. However, now I can see that the curved organelle is the golgi apparatus and F must represent the whole endoplasmic reticulum.

I believe plasma membrane proteins are synthesized in the rough endoplasmic reticulum.

FA2020 p46 Rough endoplasmic reticulum Site of synthesis of secretory (exported) proteins and of N-linked oligosaccharide addition to lysosomal and other proteins.

Free ribosomes—unattached to any membrane; site of synthesis of cytosolic, peroxisomal, and mitochondrial proteins.

Smooth endoplasmic reticulum Site of steroid synthesis and detoxification of drugs and poisons. Lacks surface ribosomes. Location of glucose-6-phosphatase (last step of glycogenolysis).

nbmeanswersownersucks  I was under the impression that translation of transmembrane proteins begins with ribosomes in the cytoplasm that then translocate to the rough ER once the signal sequence is reached by the ribosome? i.e. technically translation begins in the cytoplasm but finishes in the rough ER. Am I wrong about that? +4  
nbmeanswersownersucks  It was UWORLD 6544 about insulin translation. They state that the translation is initiated in the cytoplasm then relocates to the RER (d/t the signal sequence) and is finished there. So is there a difference in translation steps for proteins that are excreted like insulin and transmembrane proteins? +2  
nsinghey  Same, I am not sure about this. My best guess is that since insulin is not a functional protein, it is not synthesized in the RER (even though it it excreted from the cell). Actual proteins are made in the RER +2  
kevster123  I just put F cause it said transmembrane domains and I know the rough ER got a lot of balls on it that translate it through and to translate through the balls you're passing through membranes. +  
drdoom  @nbmeanswersownersucks @nsinghey et al. There is extensive discussion of this on an NBME 24 thread. This link will take you to the comments (just don't scroll up to spoil the answer for yourself!): https://nbmeanswers.com/exam/nbme24/939#1379 +  
drdoom  also, this thread from NBME 21 discusses cell transport more generally (same warnings apply! don't scroll up!): https://nbmeanswers.com/exam/nbme21/742#257 +  
brise  The question is saying where is it initially produced? It is produced in the RER, therefore F. Not asking where it's production starts- asking where is it produced etc. +  

Related discussions from other NBMEs:

https://nbmeanswers.com/exam/nbme24/939#1379

https://nbmeanswers.com/exam/nbme21/742#257

+/- drdoom(812),

^ SPOILER ALERTS. DO NOT SCROLL UP AFTER CLICKING LINKS! :)

+/- drdoom(812),