Question

The glucose-Na+ symport transports glucose into the epithelial cells lining the gut. How would import of glucose into the cells be affected by addition of a leaky Na+ channel to their plasma membrane? Choose one:

A. Glucose transport would slow because the Na+ gradient is dissipated by the Na+ channel.
B. Na+ transport would slow, but glucose transport would remain high because glucose could still be transported by the glucose-Na+ symport.
C. A leaky Na+ channel would not affect glucose transport because these two transporters are unrelated.
D. Glucose transport would increase because the Na+ gradient is strengthened by the Na+ channel.

Answer 1

A leaky Na+ channel in the plasma membrane would dissipate the Na+ gradient needed for the glucose-Na+ symport to function effectively, thus slowing down the transport of glucose into the epithelial cells lining the gut.

Step-by-step explanation:

The transport of glucose into epithelial cells lining the gut via the glucose-Na+ symport relies on the Na+ gradient across the cell membrane. If you add a leaky Na+ channel to the plasma membrane, it would dissipate the Na+ gradient, because Na+ ions would flow back into the cell without being part of the active transport process. As a result, the glucose-Na+ symport would have less of the Na+ ion gradient to use for the secondary active transport of glucose.

Therefore, the correct answer is A. Glucose transport would slow because the Na+ gradient is dissipated by the Na+ channel. The function of the glucose-Na+ symport depends on the low concentration of Na+ inside the cell compared to the outside, driven by the Na+/K+ ATPase pump. The presence of a leaky channel allows Na+ to enter back into the cell, undermining the gradient needed for the effective function of the symporter.