Overview
This lecture explains the function of the sodium-potassium pump in animal cells and how it helps maintain a cell’s resting membrane potential important for cell function.
Fish Tanks and Pumps Analogy
- Fish tanks need pumps to circulate water, similar to how cells need pumps to maintain internal conditions.
- Cell pumps require energy, often from ATP, instead of electricity.
Introduction to Cell Pumps
- Cells have microscopic pumps embedded in their membranes.
- Many cell pumps use ATP as an energy source to move substances.
- The sodium-potassium pump is an important example of these pumps.
Sodium-Potassium Pump Function
- The sodium-potassium pump helps maintain the cell’s resting membrane potential, the voltage difference between inside and outside the cell.
- At rest, the inside of most animal cells is more negative than the outside.
- The pump starts open to the inside (intracellular) and binds three sodium ions.
- ATP phosphorylates the pump, changing its shape and opening it to the outside.
- The pump releases sodium ions outside and binds two potassium ions from the outside.
- The pump releases its phosphate group, returns to its original shape, and releases potassium inside.
- This cycle repeats, moving three sodium ions out and two potassium ions in each cycle.
Active Transport and Electrochemical Gradient
- The pump moves sodium and potassium ions against their concentration gradients (active transport).
- There is a higher sodium concentration outside and a higher potassium concentration inside the cell.
- For every three positive charges out, only two come in, contributing to net negativity inside the cell.
- The pump creates an electrochemical gradient (difference in both charge and ion type) across the cell membrane.
Resting Membrane Potential and Ion Leakage
- Potassium can move out of the cell via potassium leakage channels, making the inside more negative.
- There are more potassium leakage channels than sodium leakage channels, making the membrane more permeable to potassium.
- Other ions and factors also contribute to the cell’s negative resting potential.
Importance of the Gradient
- The sodium-potassium pump's gradient is essential for processes like action potentials in neurons and muscle cells.
- Some other transport proteins, such as glucose transporters, also rely on this gradient to function.
Key Terms & Definitions
- ATP — Adenosine triphosphate, a molecule used as an energy source in cells.
- Sodium-potassium pump — A protein that moves sodium out and potassium into animal cells using ATP.
- Resting membrane potential — The voltage difference between the inside and outside of a resting cell.
- Active transport — Movement of substances against their concentration gradient, requiring energy.
- Electrochemical gradient — A combined difference of ion concentration and electrical charge across a membrane.
- Phosphorylation — The addition of a phosphate group to a protein, often changing its function or shape.
Action Items / Next Steps
- Review the ATP and diffusion videos for further understanding.
- Explore the action potential in neurons for more details on changes in membrane potential.