Endoplasmic Reticulum

ID #1274

I was reviewing the lecture where you introduced the pulse-chase reaction, and in the lecture there are two things that confused me. First, in one of the early figures on page three, the illustration shows the protein being translated into the cytosol, but then later it shows the protein leaving the cell. Is that just because the illustration is incorrect because shouldn't it be translated into the lumen of the ER if it is going to the golgi body and eventually to a secretory vesicle? And secondly, what accounts for the time difference (same lecture) between the 7 minute chase in which the proteins are found in the lumen of the golgi body and the 120 min. chase when it finally goes into the secretory vesicles?


For the first question, yes, if the end result of a pulse-chase reaction was the secretion of a protein, it wouldn't involve a free cytosolic ribosome. That ribosome was just shown like that for simplicity in setting up what a pulse-chase reaction is. For the second question, just that it takes time to get through the ER, then time to get through the Golgi, and time to be secreted, etc. If you took a time point at 4 minutes, most of your "signal" (the radioactivity) would still be in the ER, not really telling you anything.

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