You have prepared lipid vesicles (spherical lipid bilayers) that contain Na^+ -K

Question

You have prepared lipid vesicles (spherical lipid bilayers) that contain Na^+ -K^+ pumps as the sole membrane protein. All of the Na^+ -K^+ pumps are oriented in such a way that the portion of the molecule that normally faces the cytosol is in the inside of the vesicle and the portion of the molecule that normally faces the extracellular space is on the outside of the vesicle. Assume that each pump transports one Na^+ ion in one direction and one K^+ ion in the other direction during each pumping cycle (see Figure Q12-15 for how the Na^+ -K^+ pump normally functions in the plasma membrane). Predict what would happen in each of the following conditions: A. The solutions inside and outside the vesicles contain both Na^+ and K^+ ions but no ATP. B. The solution outside the vesicles contains both Na^+ and K^+ ions: the solution inside contains both Na^+ and K^+ ions and ATP. C. The solution outside contains Na^+: the solution inside contains Na^+ and ATP.

Explanation / Answer

A.With no ATP there would be no energy supplier.Thus in the absence of ATP there would be no transfer of Na + and K+ on either sides.Sodium potassium pumps work on the principle of active transport which is primarily done by ATP.There would be no transport of either types of ions in the absence of ATP.

B. In the presence of ATP Na+ ions which have diffused inside will be pumped outside and K+ wiill move in the opposite direction i.e from outside to inside.Usually the Na+ ion conc. remains high outside and they keep on diffusing inside and reverse is true for K+.Their conc. is high inside and low outside.In the presence of ATP by the process of active transport Na+ is pumped outside and K+ is pumped inside.

C.If the concentration of Na+ is equal both on the inside and outside there will be no movement of Na+ ion on either side.The movement of Na+ depends on its conc. when it is high outside and low inside , it moves inside due to diffusion .In the presence of ATP active transport occurs which pushes Na+ ion outside in exchange of K+ ions.

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