Cell-cell junctions · USMLE Step 1

What is the basic structural unit of a gap junction channel in vertebrate cells?

  1. Two cadherin molecules from opposite cells clasping together
  2. A single connexon of six connexins that pairs with no partner
  3. Two connexons, each six connexins, one from each adjacent cell
  4. A paired claudin and occludin protein complex
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Correct answer: Two connexons, each six connexins, one from each adjacent cell

A gap junction channel is formed by a connexon (hemichannel) made of six connexin proteins in one cell membrane; when that hemichannel docks with a connexon on an adjacent cell, they form a continuous intercellular channel.

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