Co-transport

What is co-transport?

A type of active transport in which 2 molecules move at the same time.

Describe what happens at a Sodium-Potassium pump.

1) Carrier protein is open on the inside of the cell where 3 sodium ions are able to bind to their sodium ion binding site.

2) An ATP molecule binds to its binding site and one of its phosphate groups is hydrolysed to produce ADP, Pi and release energy.

3) This energy release causes a conformational change t occur where the protein then opens at the outside of the cell, releasing the sodium ions.

4) Thus then enables 2 potassium ions to bind to their binding site in the protein. The Pi unbinds causing the protein to go back into its original shape, releasing the K+ ions into the inside of the cell.

Do the Na+ and K+ ions move along or against their concentration gradient?

They actively transport against their concentration gradient.

How does glucose diffuse into the bloodstream from the small intestine?

- A sodium-potassium pump causes sodium to diffuse out of the epithelial cell into the bloodstream which decreases the concentration of Na+ inside the cell.

- Therefore, because of an abundance of Na+ being inside the lumen of the intestine, the Na+ ions move along their concentration gradient into the cell (passive transport).

- The large amount of Na+ ions diffusing passively releases energy and causes glucose molecules from the lumen of the intestine to move against their concentration gradient (actively transport) to the inside of the cell through a co-transport protein.

- This means that now, the glucose molecules can move passively, through facilitated diffusion from the cell into the blood.