Sodium-Potassium Pump Function

Overview

This lecture explains the function and importance of the sodium-potassium pump in animal cells, with a focus on how it maintains the resting membrane potential.

Fish Tanks vs. Cellular Pumps

• Fish tanks use mechanical pumps to move air or water, powered by electricity.
• Cells use protein pumps, powered by ATP, to move ions across membranes.

The Sodium-Potassium Pump

• The sodium-potassium pump is a protein that requires ATP to function.
• It maintains the resting membrane potential in animal cells.
• The pump moves sodium (Na⁺) and potassium (K⁺) ions against their concentration gradients (active transport).
• For each cycle, the pump exports 3 Na⁺ ions out and imports 2 K⁺ ions in.
• This activity helps create and maintain an electrochemical gradient across the cell membrane.

Mechanism of the Sodium-Potassium Pump

• The pump opens to the inside of the cell and binds 3 Na⁺ ions.
• ATP phosphorylates the pump, causing it to change shape and face the outside.
• 3 Na⁺ ions are released outside the cell.
• The new shape allows 2 K⁺ ions to bind from the outside.
• The phosphate is released, and the pump returns to its original shape, releasing K⁺ ions inside the cell.
• The cycle repeats to continually maintain Na⁺ and K⁺ gradients.

Resting Membrane Potential and Electrochemical Gradient

• The inside of most cells is more negative compared to the outside at rest.
• The pump results in higher K⁺ inside and higher Na⁺ outside the cell.
• More K⁺ leakage channels exist, making the membrane more permeable to K⁺ at rest.
• Outward movement of K⁺ ions tends to make the inside of the cell more negative.
• The sodium-potassium pump and ion gradients contribute to the cell’s ability to respond to stimuli (e.g., action potentials).
• Other proteins, such as glucose transporters, also rely on the electrochemical gradient created by the pump.

Key Terms & Definitions

• Resting Membrane Potential — the voltage difference across a cell’s membrane at rest.
• Sodium-Potassium Pump (Na⁺/K⁺-ATPase) — a protein that uses ATP to pump 3 Na⁺ out and 2 K⁺ into the cell.
• Active Transport — movement of substances against their concentration gradient using energy (ATP).
• Electrochemical Gradient — combined effect of ion concentration and charge difference across a membrane.
• Phosphorylation — the process of adding a phosphate group to a protein, often changing its shape and function.
• Leakage Channel — a protein channel that allows certain ions to passively move across the cell membrane.

Action Items / Next Steps

• Watch the ATP and diffusion videos for more background.
• Explore the action potential for further understanding of cellular responses.
• Review other ions that contribute to resting membrane potential.