Question

What strategy/structure prevents Na /Glucose symporters from laterally diffusing from the apical side to the lateral or basal sides of the cell?

a. Tight junctions form a ring of protein around the cell which connects to neighboring cells. This forms a physical barrier restricting lateral diffusion within the membrane.
b. The Na+/Glucose symporters are anchored to the apical side, where they are originally delivered through vesicular trafficking, through protein-protein interactions with the cytoskeleton.
c. Extracellular matrix proteins unique to the intestinal lumen side interact with extracellular side of the Na+/Glucose symporters.
d. None of these

Answer 1

a. Tight junctions form a ring of protein around the cell which connects to neighboring cells. This forms a physical barrier restricting lateral diffusion within the membrane.

Step-by-step explanation:

Epithelial cells in the small intestine act absorbing nutrients from the digestive tract. The cell membranes in these cells are divided into two domains: the apical domain specialized in nutrient absorption, and the basolateral domain, which transfers the absorbed nutrients to the blood vessels.

In order to maintain these functions differentiated, the mobility of proteins must be restricted to the pertinent domains. One of the mechanisms to achieve this is the formation of tight junctions between the adjacent cells of the epithelium. This acts as a barrier to the movement of lipids and membrane proteins. As a result, proteins can diffuse within their domains but can not cross from one domain to the other.

These tight junctions are formed by interactions between strands of transmembrane proteins, and generally, associate with adherent unions and desmosomes forming an union complex.