All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump.
-OUTSIDE CELL B. ([Na+]low, [K+]high) or ([Na+]high,[K+]low
C. (excess + charge) or (excess - charge)
-(BETWEEN) A. (3[Na+]v,2[K+]^)，（2[Na+]^,3[K+]v), (3[Na+]^,2[K+]v)
-INSIDE CELL D. ([Na+]low,[K+]high) or ([Na+]high,[K+]low)
E. (excess + charge) or (excess - charge)
B.[Na+]high [K+]low C. excess + charge
A. 3 Na+ ^ 2 K+ v
D. [Na+]low [K+]high E. excess - charge
-Active transport by the sodium-potassium pump follows this cycle.
1. Three Na+ ions from the cytosol bind to the pump.
2. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP.
3. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell.
4. The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released.
5. Release of the phosphate group causes another conformational change in the pump. 6. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol.
The net result is that the concentration of Na+ is higher outside the cell and the concentration of K+ is higher inside the cell. In addition, one more positive charge has been transported out of the cell than into the cell, leaving the outside of the cell with an excess positive charge and the inside with an excess negative charge. Thus, the sodium-potassium pump creates both chemical gradients and charge differences across the plasma membrane.
The function of the sodium-potassium pump in animal cells (and the proton pump in bacteria and plant cells) is essential to many cell functions. It prevents chemical and electrical gradients across the plasma membrane from reaching equilibrium (at which point the cell would be dead) and powers many types of active transport across the plasma membrane.

Easier diffusion of polar pumps and charged molecules, such as carbohydrates, amino acids, nucleosides, and ions, cross the plasma membrane. 3 sodium will move from inside to outside, while 2 potassium will move from outside to inside. This movement is done to maintain a gradient across the membrane. Due to ion movement, sodium ions will become higher outside the cell, while potassium ion concentration decreases. Due to 3 sodium the outward movement of the change became positive (+). ion movement the concentration of sodium ions will become lower inside the cell while the concentration of potassium inside will increase. This change decreases the charge therefore the charge inside the membrane becomes negative (-).

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