The cylindrical channels in gap junctions are made of (1) connexin. Connexins are integral membrane proteins that assemble into hexameric units called connexons or hemichannels, and two connexons from adjacent cells dock together to form a full gap junction channel. Each channel thus consists of twelve connexin subunits, forming a direct cytoplasmic bridge for communication between neighboring cells.​

Introduction: Gap Junctions and Cellular Communication

Gap junctions are specialized intercellular connections that facilitate direct cytoplasmic exchange of ions and small molecules between neighboring cells. This rapid communication is crucial for tissue coordination, particularly in excitable tissues like heart and brain.​

Connexin Structure and Assembly

• Connexins are transmembrane proteins that organize into hexameric units called connexons (hemichannels).​

• Two connexons—one from each adjacent cell—dock together to form the full gap junction channel, creating a cylindrical pore through the membrane.​

• Each gap junction channel comprises 12 connexin subunits arranged in a circular fashion.​

Why Other Proteins Are Incorrect

• Collagen: ECM structural protein, not involved in forming channels.

• Fibronectin: ECM glycoprotein, mainly functions in adhesion and migration.

• N-CAM: Neural cell adhesion molecule, does not form gap junction channels.

Connexin is unique in creating the architecture of gap junction channels, directly mediating cell-to-cell connectivity.​

Comparison Table

Conclusion

• The cylindrical channels of gap junctions are composed of connexin proteins, not collagen, fibronectin, or N-CAM.​

• Connexins are vital for direct cell-to-cell signaling in multicellular organisms.