Cell Membranes Problem Set

Co-transport of nutrients across the intestinal cell membranes is an active process that can move glucose against a concentration gradient. The energy requiring step for co-transport:

A. The Na⁺K⁺ATPase that pumps Na⁺ from the cell into the lumen of the intestine.

B. The permease that allows glucose and Na⁺ into the cell requires ATP.

C. The permease that pumps glucose from the cell into the blood requires ATP.

D. The Na⁺K⁺ ATPase that pumps Na⁺ from the cell into the blood, maintaining low Na⁺ levels in the cell.

Tutorial

Co-transport system of intestinal epithelial cells

The Na⁺K⁺ ATPase uses the energy of ATP hydrolysis to move Na⁺ out of the epithelial cells lining the intestine and into the blood. The reduced concentration of Na⁺ inside the cell coupled with high Na⁺ inside the lumen of the intestine results in a driving force for the movement of Na⁺ into the cell.

The cotransporters in the membrane of the epithelial cell facing the intestine allow Na⁺ to enter only when accompanied by either glucose or one of the amino acids (each have their own set of co-transporters).

Glucose then moves into the blood through the permease in the membrane between the cell and the blood.Thus, ATP is used as an energy source to drive Na⁺ out of the cell, resulting in glucose transport from the intestine to the blood.

Membrane proteins must have an asynchronous distribution on the cell membrane for the system to function. This is an example of the membrane synthetic apparatus determining where in a membrane a protein should be localized. The Na⁺K⁺ ATPase must be localized to the membrane between the cell and our blood.

Cotransport systems of the intestinal epithelial cells

Problem 5 | Answer | Problem 6