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Describe the EP and CP of the cell when K+ is at equilibrium.
EP and CP are exactly equal. There is no net flux of K+.
What occurs to the inside of the cell when K is driven outward?
The inside has a slight increase in negative charge
What are the concentrations of K+ and Na+ when the cell is at equilibrium?
Kout = 4 mM
Kin = 120 mM
Nain = 14
What does a positive CP and negative CP mean?
High CP = high concentration inside the cell, low concentration outside; efflux
Low CP = low concentration inside the cell, high concentration inside; influx
(This has NOTHING to do with charge of ions)
What occurs in the inside of the cell is negative (EP is negative)? Positive (EP is positive)?
Negative EP = negative ions repelled and positive ions attracted
Positive EP = negative ions attracted and positive ions repelled
What are some gating mechanisms in membrane channels?
3) Voltage and Ligand
How many osmoles are there for each of the following?
1) 1 M glucose
2) 1 M MgCl2
3) 1M NaCl
1) 1 Osmole glucose
2) 3 Osmoles MgCl2
3) 2 Osmoles NaCl
Does water move to an area of low osmolarity or high osmolarity?
Water moves from low osmolarity to high osmolarity.
What is osmolarity?
The number of individual particles formed upon dissociation of a solute in solution.
What is the cause of osmotic pressure?
A difference is osmolarity on two sides of a membrane
What does a relection cooefficient of 1 mean? 0?
1 = membrane is impermeable to solute; only water flows across
0 = membrane is fully permeable to solute
What is hydrostatic pressure?
Hydrostatic pressure is a force exerted that causes water to move. When hydrostatic pressure equals osmotic pressure, no change in volume occurs.
What is osmosis?
The net movement of water resulting in volume change.
This only occurs when one solute is impermeable.
Summarize how water moves in capillaries?
A beating heart creates hydrostatic pressure which drives water into the iterestitial space. Proteins in capillaries cause an osmotic pressure and draw water back into the capillary (oncotic pressure).
What are some reasons that diffusion isn't used?
- Some cells are too large (facilitated diffusion). Ex - glucose
- Some molecules are too charged to diffuse across bilayer
- Movement against concentration gradient is sometimes needed (Active transport)
What are some characteristics of carrier proteins?
- Have specificity
What are some characteristics of facilitated diffusion?
- Carrier protein involved
- ATP is NOT required
- Solutes move from high conc to low conc (at a higher rate than simple diffusion)
- Equal binding affinities on intra and extracellular sides
What are some characterisitcs of active transport?
- Carrier protein involved
- Energy required (ATP or Na+ gradient)
- Unequal binding affinities of carrier (higher affinity on area of low conc)
Describe the Na-K pump
- Uses Na-K ATPase
- pumps 3 Na out and 2 K in to maintain the gradient