Sodium-Potassium Pump Function

Overview

This lecture explains the function and importance of the sodium-potassium pump in animal cells, focusing on its role in maintaining resting membrane potential and active transport of ions.

Introduction to Pumps

• Fish tanks use pumps to aerate water and filter for fish health.
• Biological cells also use "pumps" to move substances across cell membranes.
• Cellular pumps require energy, often supplied by ATP (adenosine triphosphate).

Sodium-Potassium Pump Function

• The sodium-potassium pump uses ATP to transport ions across the cell membrane.
• It helps maintain the resting membrane potential (the voltage difference across a cell's membrane at rest).
• The pump is a protein in the cell membrane that moves ions against their concentration gradients.
• It opens to the inside of the cell and binds three sodium (Na⁺) ions.
• The pump is phosphorylated by ATP, changing its shape and releasing sodium outside the cell.
• It then binds two potassium (K⁺) ions from outside the cell.
• The phosphate group is released, and the pump returns to its original shape, releasing potassium inside the cell.
• This cycle repeats continuously.

Active Transport & Gradients

• The pump moves sodium out and potassium in, both against their concentration gradients (active transport).
• Result: high sodium concentration outside the cell, high potassium inside.
• For each cycle, three positive ions exit (Na⁺) while two enter (K⁺), contributing to a more negative charge inside.
• This activity sets up an electrochemical gradient (difference in charge and chemical concentration across the membrane).

Resting Membrane Potential & Ion Channels

• Most cells are more negative inside than outside at rest.
• Potassium tends to leak out of cells due to more potassium leakage channels, increasing negativity inside.
• Fewer sodium leakage channels reduce sodium flow into the cell.
• Other ions besides sodium and potassium also influence the resting potential.

Importance of the Gradient

• The electrochemical gradient enables action potentials and is essential for nerve and muscle function.
• Other transport proteins use this gradient to move substances like glucose into the cell.

Key Terms & Definitions

• Resting membrane potential — the voltage difference between the inside and outside of a cell at rest.
• Sodium-potassium pump — a membrane protein that uses ATP to move 3 sodium ions out and 2 potassium ions into the cell.
• Active transport — movement of molecules against their concentration gradient, requiring energy.
• Electrochemical gradient — a combination of concentration (chemical) and charge (electrical) differences across a membrane.
• Phosphorylation — the addition of a phosphate group (from ATP) to a protein, changing its shape and function.

Action Items / Next Steps

• Review the ATP and action potential videos for deeper understanding.
• Explore diffusion and how leakage channels affect membrane permeability.