During intravesicular transport, a vesicle was able to bud from the ER membrane, but its cargo did not make it to the cis-Golgi network. Which of the following conclusions can you make?
A. There was nothing wrong with the coat proteins
B. There could have been something wrong with the SNARES
C. There is not necessarily a problem because if this vesicle contains secreted proteins, it should go straight from the ER to the plasma membrane
D. All of the above
E. A and B only Notes
The correct answer and explanation is:
The correct answer is B. There could have been something wrong with the SNAREs.
Explanation:
Intravesicular transport involves several key proteins that facilitate the movement of vesicles from one compartment to another. When a vesicle buds from the ER membrane, it is coated with coat proteins like COPII, which help the vesicle form and move toward its destination. In this case, the vesicle failed to deliver its cargo to the cis-Golgi network. The most likely explanation for this failure is a problem with the SNAREs.
SNAREs (Soluble NSF Attachment Protein Receptors) are proteins involved in the fusion of vesicles with their target membranes. The vesicle carries v-SNARE proteins, while the target membrane (such as the cis-Golgi membrane) has t-SNAREs. The interaction between v-SNAREs and t-SNAREs facilitates the fusion of the vesicle with the target membrane, allowing cargo to be delivered. If the SNAREs do not function properly, vesicle fusion cannot occur, and the cargo will not be delivered to the cis-Golgi.
Option A (Nothing wrong with the coat proteins) can be ruled out because the vesicle successfully budded from the ER, indicating that the coat proteins (like COPII) were functioning properly to form and transport the vesicle.
Option C (The vesicle could go straight from the ER to the plasma membrane) is not necessarily true in this case. If the vesicle contains secreted proteins, it typically goes through the Golgi network for processing and modification before being directed to the plasma membrane. Direct transport from the ER to the plasma membrane is less common and usually involves specialized vesicles like those for membrane proteins.
Therefore, the most reasonable conclusion is that a problem with the SNAREs could be preventing the fusion of the vesicle with the cis-Golgi network.