Question 4

[srraghav1542]

I was under the impression that proteins destined for extracellular secretion bud off of the RER and are transported to the Golgi encased in the membrane of the RER. Then the vesicle fuses with the Golgi, modifications occur, and lastly, it buds off of the Golgi and is directed to the plasma membrane. This would be the only way for the inside of the RER to be continuous with the inside of the Golgi, which is continuous with the extracellular environment. If this is the case, then the answer would be B. Endoplasmic Reticulum. Please see the excerpt from Nature below:

The sequential transfer of material between membrane compartments of the exocytic pathway involves coated vesicular and tubular carriers. Therefore, proteins with destinations beyond the ER need to be sorted away from ER residents and packaged into transport vesicles to undergo this next step. ER-derived vesicles are formed by the binding of the protein complex COPII to the external side of the membrane, followed by the selection of cargo. Following budding, these vesicles are directed towards the Golgi complex and then uncoat prior to membrane fusion and cargo delivery.

Please explain...

[admin]

Your analysis of the purpose of the two organelles is absolutely correct. The purpose of the question was just to underline that it is the main purpose of the rER to synthesize protein whereas it is the prime purpose of the GA to modify and package for export. The rER does not directly package for export.

You may find the question unfair but it happens to 1-2 questions per exam even on the real MCAT. The scaled score was created to minimize the impact of 1-2 questions.

[admin]

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