You are tracing the path of a secretory protein from its synthesis to its export

Question

You are tracing the path of a secretory protein from its synthesis to its export from a
cell. You have added radioactive amino acids to a culture of cells, and then measured the
amount of radioactivity that shows up in the proteins of each of the following cell
fractions at different times after the addition. List the order in which the proteins of these
fractions first exhibit radioactivity:

I secretory vesicles
II Golgi complex
III rough ER
IV smooth ER
V nucleus

a. III ?II ?I? out of the cell
b. III? II? IV? V ?out of the cell
c. V? III? II? I ?out of the cell
d. IV? III ?II ?I ?out of the cell
e. II? III? IV? I? out of the cell

Explanation / Answer

secretory protein path:
Endoplasmic Reticulum-->cis Golgi cisternae --> medial Golgi cisternae --> trans Golgi Cisternae --> Plasma membrane and there to Extra Cellular Space
most near is
a)

b) is wrong because it doesent go to nucleus anytime

c) is wrong because translation doesent happen in nucleus

d) is wrong because smooth ER has very little to do with protein synthesis, its main operations are : synthesize lipids and steroids, metabolize carbohydrates and steroids (but not lipids), and regulate calcium concentration

e) is wrong because golgi is AFTHER ER and not before.+ smooth doesent do protein synthesis

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