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Cell Membranes Problem Set

Problem 8: Cotransport

Tutorial to help answer the question

Cotransport systems of the intestinal epithelial cells include the_________ in the intestine-facing membrane, the energy requiring _____________ facing the blood, and the ______________, allowing facilitated diffusion of glucose out of the cell.

A. permease, cotransporters, Na+K+ ATPase
B. cotransporters, CFTR, permeases
C. Na+K+ ATPase, cotransporters, permeases
D. cotransporters, Na+K+ ATPase, permeases

Tutorial

Cotransport system
The diagram illustrates the cotransport system of our intestinal epithelial cells.
  • The Na+K+ ATPase moves Na+ out of the epithelial cells lining the intestine and into the blood.

  • The low concentration of Na+ inside the cell and the high concentration of Na+ inside the lumen of the intestine provide a diving force for the net movement of Na+ inside 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 cotransporters).

  • Thus, using ATP as an energy source to release Na+ inside the cell results in the transport of glucose from the intestine to the blood.

Cotransport systems of the intestinal epithelial cells

Membrane proteins
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 can determine 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.

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