Question 195

Question:

Several contiguous cells are labeled with a fluorescent dye that cannot cross cell membranes. One cell is experimentally bleached with light that destroys the dye, but the cell soon recovers dye fluorescence. This recovery is best explained by the presence of which of the following structures between the bleached cell and its fluorescent neighbors?

Correct Answer: C.  Gap junctions

Gap junctions (choice C) allow transfer of chemical and electrical signals between cells. The key structural component of gap junctions is the connexon, a hollow cylinder made up of transmembrane proteins. Gap junctions allow cells to coordinate activities with each other, and are found in nerve cells, cardiac muscle, smooth muscle, and liver cells.
Basal lamina (choice A) is a layer of extracellular matrix on which the epithelium sits.
Desmosomes (choice B) are structures that bind to intermediate filaments between adjacent cells in order to hold them together.
Glycosaminoglycans (choice D) are the carbohydrate portions of proteoglycans, or mucopolysaccharides, that form the major structural components of the extracellular matrix.
Tight junctions (choice E) are barriers that form a belt-like structure encircling epithelial cells along their apical surface. They prevent movement of small molecules between the two cells.