19. Charles expresses GFP that has a signal sequence so it gets imported into th

Question

19. Charles expresses GFP that has a signal sequence so it gets imported into the ER (ER-GFP). He
has treated cells expressing the ER-GFP with a drug that disrupted a step in the secretory pathway
such that many vesicles accumulate in the cell.

A. If he isolates the vesicles, will he be able to look for coat protein complexes to help distinguish which membranes the vesicles came from?

B. Are there any other proteins or characteristics of the vesicles that may allow him to determine the origin
of the vesicles?

Explanation / Answer

A. If Charles isolates these vesicles, he will be able to distinguish the origin of the vesicles based on the coat protein complexes. There are three types of coat protein complexes: Clathrin COPI COPII Clathrin coat proteins are present on vesicles which transport proteins between Golgi apparatus and plasma membrane, Golgi and endosomes and plasma membrane and endosomes. COPI coated vesicles transport proteins in the retrograde transport from Golgi to ER. COPII coated vesicles transport proteins in the anterograde transport from ER to Golgi. -------------------------------------------------- Hence, if the vesicles Charles isolates contain COPII, they are responsible for the movement of proteins from ER to Golgi. These vesicles originate from the ER. --------------------------------------------------- B. The proteins present in the vesicles have signal sequences which enable them to be transported to the right organelle. These signal sequences do not indicate the origin of the vesicles but indicate the organelle to which the protein needs to be sent. There are no other characteristics which can help Charles identify the origin of the vesicles.

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