Let's break down how the sodium-potassium pump affects the distribution of charge across the plasma membrane.
### Step-By-Step Explanation:
1. Overview of the Sodium-Potassium Pump:
- The sodium-potassium pump is a type of active transport mechanism found in the plasma membrane of cells.
- It functions to maintain the concentration gradients of sodium (Na⁺) and potassium (K⁺) across the membrane.
2. Ion Concentration Gradients:
- Typically, there is a high concentration of sodium ions (Na⁺) outside the cell and a low concentration inside.
- Conversely, there is a high concentration of potassium ions (K⁺) inside the cell and a low concentration outside.
3. Mechanism of the Pump:
- The pump actively transports 3 sodium ions (Na⁺) out of the cell and 2 potassium ions (K⁺) into the cell.
- This process requires energy in the form of ATP since it is moving ions against their concentration gradients.
4. Charge Distribution:
- For each cycle of the pump, 3 positively charged sodium ions (Na⁺) are moved out, and 2 positively charged potassium ions (K⁺) are moved in.
- This results in a net movement of one positive charge out of the cell per cycle.
5. Resulting Membrane Potential:
- The removal of more positive charges than are brought in creates an excess of negative charge inside the cell and a relative excess of positive charges outside the cell.
- This difference in charge across the membrane is referred to as the membrane potential.
6. Impact on Membrane Potential:
- The sodium-potassium pump contributes to the resting membrane potential by maintaining the concentration gradients of Na⁺ and K⁺.
- The typical resting membrane potential is negative on the inside (around -70mV in neurons).
### Summary:
The sodium-potassium pump helps establish and maintain the electrochemical gradients of Na⁺ and K⁺ across the plasma membrane. By actively transporting 3 Na⁺ out of the cell and 2 K⁺ into the cell, the pump creates a net loss of positive charge from the cell interior. This results in a higher positive charge outside the cell compared to inside, thus generating a negative resting membrane potential within the cell. This difference in charge is crucial for various cellular processes, including the conduction of electrical signals in neurons.
