Question

Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure Q11-50A. When a molecule that chelates calcium is added to the cell culture medium, you observe a redistribution of that protein around the entire cell, shown in Figure Q11-50B. Which is most likely to be true about the role of calcium in maintaining an apical distribution of protein A? (a) calcium is required to maintain the structural integrity of the junctional complex

(b) calcium is required for the binding of the junctional proteins to the cell cortex
(c) calcium is a structural component of protein A
(d) calcium inhibits intracellular transport of protein A

Answer 1

Calcium is crucial for maintaining the structural integrity of cell junctions responsible for the apical localization of proteins. Removal of calcium through chelation disrupts junctions like tight junctions and adherens junctions, leading to the redistribution of apically expressed proteins.

Step-by-step explanation:

The role of calcium in maintaining an apical distribution of protein A is most likely (a) calcium is required to maintain the structural integrity of the junctional complex.

Epithelial cells depend on calcium for the formation and maintenance of cell junctions, such as tight junctions, adherens junctions, and desmosomes, which are necessary for cellular adhesion and polarity. These structures are vital for separating the apical and basal compartments of cells, and they rely on calcium to function properly. When calcium is chelated and removed from the environment, proteins like cadherins and integrins that are involved in these junctions cannot maintain their structure or function effectively.

This causes a redistribution of protein A because the adherens and tight junctions that would typically localize it to the apical surface can no longer maintain its restricted distribution. Turning the protein from an apically localized one to being distributed around the entire cell perimeter.