Definition of exocytosis in cell transport: Which statement correctly describes exocytosis of proteins?
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ASecretion of proteins out of the cell across the plasma membrane into the extracellular space
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BSecretion of proteins out of the cell into the intracellular space
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CUptake of macromolecules from the extracellular space into the cell (endocytosis)
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DUptake of macromolecules from the intracellular space into the cell
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ERelease of proteins only from mitochondria to cytosol
Answer
Correct Answer: Secretion of proteins out of the cell across the plasma membrane into the extracellular space
Explanation
Introduction / Context: Cells move large cargo by vesicular transport. Exocytosis is the outward, secretory pathway delivering proteins, lipids, and signaling molecules to the plasma membrane or extracellular milieu.
Given Data / Assumptions:
- We consider secreted proteins, neurotransmitters, and membrane proteins being delivered to the surface.
- Question asks for the correct definition.
Concept / Approach: In exocytosis, secretory vesicles derived from the Golgi apparatus fuse with the plasma membrane. The vesicle lumen becomes continuous with the extracellular space, releasing soluble cargo and inserting membrane proteins/lipids into the plasma membrane.
Step-by-Step Solution: Differentiate exocytosis (outward) from endocytosis (inward). Select the option explicitly stating movement out to extracellular space. Eliminate options describing uptake or internal spaces. Confirm terminology matches standard cell biology usage.
Verification / Alternative check: SNARE-mediated membrane fusion and calcium-triggered exocytosis (e.g., synaptic vesicles) exemplify this process.
Why Other Options Are Wrong: (b, d) misuse of terms; (c) describes endocytosis; (e) is unrelated to the general definition.
Common Pitfalls: Confusing directionality; forgetting that vesicle lumen becomes extracellular after fusion.
Final Answer: Secretion of proteins out of the cell across the plasma membrane into the extracellular space.