Cell Biology MCAT Practice Question
A 34-year-old woman with a history of recurrent infections and poor wound healing undergoes genetic testing that reveals mutations affecting SNARE protein function. Researchers studying her cells observe that while vesicles can dock at target membranes normally, they fail to fuse. When SNARE complex formation is artificially blocked after docking but before fusion, the defect persists. Which of the following best explains why docking of vesicles is insufficient for membrane fusion? Which of the following best explains why docking of vesicles is insufficient for membrane fusion without functional SNARE complexes?
Answer choices
- ATethering proteins have already released from the docked vesicle, leaving no mechanism to bridge the gap between membranes
- BSNARE complexes are required to generate the conformational energy needed to overcome the repulsive forces between lipid bilayers and drive membrane fusionCorrect answer
- CRab GTPases become inactivated once docking occurs and cannot be reactivated without SNARE-mediated signaling
- DCalcium-dependent exocytosis cannot proceed without SNARE proteins triggering the opening of voltage-gated calcium channels
- EPhosphatidylinositol 3-phosphate is depleted during the docking phase, and SNARE proteins are needed to regenerate phosphoinositide lipids
- FActin polymerization, which is required for the final stages of membrane fusion, cannot be initiated without SNARE protein-regulated cdc42 activation
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