Indirect Active Transport: Sodium Symport Drives the Uptake of Glucose

Question 1

How does most glucose get into and out of our cells?

Answer 1

facilitated diffusion

Question 2

To get glucose into and out of our cells, some cells use…

Answer 2

Na+/glucose symporter

-cells lining the intestine take up glucose and some amino acids despite concentration gradients

Question 3

How is a steep Na+ gradient maintained across the plasma membrane? What does this do?

Answer 3

• Via Na+/K+ pump

- used to provide the energy needed

Question 4

Proteins responsible for sodium symport are called?

Answer 4

sodium-dependent glucose transporters, or SGLT proteins

Question 5

Mechanism for Na+/glucose symporter (6)

Answer 5

1. two external Na+ions bind to their sites on the symporter, which is open to the exterior
2. allows one molecule of glucose to bind
3. conformational change in the protein exposes the glucose and Na+ inside the cell
4. the two Na+ ions dissociate in response to the low internal Na+ concentration
5. locks the symporter in its inward facing conformation until the glucose dissociates
6. loss of glucose frees the symporter to return to the outward facing conformation