Cell Membrane Transport: Examples of Active Transport

Question 1

Describe the Na+/K+ pump.

How many comformations does the Na+/K+ pump have?

Answer 1

pumping of both Na+ and K+ against their concentration gradients

three Na+ moved out and two K+ moved in per molecule of ATP hydrolysed

the Na+/K+ pump has two conformations

Question 2

Describe the mechanism of the Na+/K+ pump

Answer 2

1. 3 Na+ bind to E1 conformation
2. this triggers phosphorylation of the subunit by ATP
3. pump undergoes a shift to the E2 conformation
4. 2 K+ bind to the E2 conformation on the outside of the cell
5. this triggers dephosphorylation of the subunit by ATP and a return to the E1 conformation
6. conformational change, K+ carried inside of the cell and released

Question 3

Describe the indirect active transporter mechanism steps for the Na+/Glucose symport OR SGLT

Answer 3

1. 2 Na+ externally bind to sites on the symporter
2. as this symporter is open externally to the cell, glucose is free to now bind
3. a conformational change occurs which exposes the glucose and Na+ inside the cell
4. 2 Na+ 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 fres the symporter to return to the outward-facing conformation

Question 4

Describe the Bacteriorhodopsin Proton Pump:

What it does and what it looks like.

Answer 4

• small integral membrane protein in the plasma membrane of archaea that uses energy from photons of light to drive active transport of protons out of the cells
• creates an electrochemical proton gradient that powers synthesis of ATP by an ATP synthase
• seven alpha helical membrane spanning segments that form a cylindrical shape