16. You are at a cocktail party and overhead an obnoxious academic trying to imp

Question

16. You are at a cocktail party and overhead an obnoxious academic trying to impress a group of students by saying: “The interior space, or lumen, of each membrane-enclosed compartment along the biosynthetic–secretory and endocytic pathways is topologically equivalent to the lumen of most other membrane-enclosed compartments and to the cell exterior.” Your friend whispers in your ear—“what is that guy talking about?” Rephrase, in plain language, the statement above:

17. Aside from the cell surface, where else can a secretory protein end up?

Explanation / Answer

16. Basically what he is trying to say is that the lumen of the organelles involved in the biosynthetic-secretory and endocytic pathway (endoplasmic reticulum, golgi body, vesicles, lysosomes, endosomes) is similar to the lumen of other organelles like mitochondria and the extracellular environment.

The lumen of organelles and the extracellular environment is known to be oxidative while the cytosol is reductive, and so their contents never mix because of the presence of the membranes surrounding the organelles.

17. Aside from the cellular membrane, secretory proteins can end up in the membranes of the endoplasmic reticulum, Golgi body, in the lysosomes as well as in the extracellular environment.

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