Membrane Transport Mechanisms · USMLE Step 1

If a cell needs to export a large protein product (e.g., a hormone) into the extracellular space, which membrane transport mechanism is most appropriate?

  1. Simple diffusion
  2. Primary active transport
  3. Exocytosis
  4. Facilitated diffusion via channels
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Correct answer: Exocytosis

Exocytosis is the vesicular transport mechanism by which cells export large proteins or other bulky molecules: vesicles fuse with the plasma membrane and release their contents extracellularly, a process that requires energy.

Difficulty: Medium Question 14 of 24

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