Membrane Potential

QUICK REVIEW

This is an example of what kind of transport? Passive (Simple Diffusion)

This is an example of what kind of transport? Primary Active Transport ATP -> ADP + P i

Membrane Potential  The voltage across the plasma membrane that is the result of a difference in electrical charge inside vs outside the cell  It is called potential b/c it represents stored electrical energy that can be used to do work at some future time  Measured in millivolts (mV)  Requires active transport (Na+/K+ pump) to maintain

Setting up the Membrane Potential Certain anions (-charged particle) are confined to inside of cell They attract cations (+ charged particles) inside What effect might all these solutes inside the cell have on the water outside the cell? –Draws water in –Causes swelling & possibly lysis (bursting) of cell Proteins - Phosphates - + -

Inflow of water stimulates the Na+/K+ pump Pumps 3 Na+ out and 2 K+ in –Is this active or passive transport? What is the net effect on the cell? –More + is leaving Setting up the Membrane Potential (cont.)

The cell membrane is more permeable to K+ (compared to Na+) In a normal leaky cell would K+ leak in or out? Would Na+, leak in or out? Overall, 3 Na+ leak in and 2 K+ leak out. Is this active or passive transport? The Na+/K+ pump controls the leak… and does exactly opposite 3 Na+ out and 2K+ in Why do we use ATP for this? ATP -> ADP + Pi Less K+ leaks out because it is attracted to the negative charge inside the cell More Na+ leaks in because it is attracted to the – charge inside the cell

What’s so great about the Na+/K+ pump? It sets up a steep concentration gradient across the cell membrane where there is a lot more Na+ outside and more K+ inside. This is potential energy Na+ wants to come in

Heat production –Thyroid hormone stimulates cells to produce more Na+/K+ pumps in winter months –why? –Heat is generated when the pump consumes ATP –This compensates for the heat we lose to the cold environment What’s so great about the Na+/K+ pump? (cont.)