USMLE Step 1 Question 377

Question:

A researcher is investigating epithelial cell junctions. She injects one cell with a liquid dye and notes that the dye seeps into the adjacent cell. Which epithelial cell junction is most likely to have allowed the dye through to the adjacent cell?

Correct Answer: B.  Gap junction

Gap junctions (choice B) allow adjacent cells to communicate with one another. They are made up of connections with central channels which allow small substances (< 1000 daltons) to pass between cells. Desmosome (choice A), also known as a macula adherens, is a discrete site of attachment between cells that stabilizes the cell to cell connection; however, it does not allow any substance to pass between the cells. Hemidesmosomes (choice C) attach the cell to its underlying extracellular matrix and are not involved in cell to cell communication. Zona adherens (choice D) is made up of actin filaments and E-cadherin and participates in stabilizing the border between cells. It does not allow communication between cells. Zona occludens (choice E) is a tight junction between cells that prevents substances from diffusing across the intracellular space. From basal surface: hemidesmosomes (ECM/basement membrane) --> zona adherens –> macula adherens –> zona occludens/tight junction