What is bulk flow?
The movement of a solutionfrom one compartment to another due to a pressure gradient
What is simple diffusion?
The movement of a solute through a membrane due to an electrochemical gradient. No transport assistance is involved.
In simple diffusion, how do we know what direction the solute will move?
Whatever gradient exists will push the solute from High to Low (electric: High potential to low potential, concentration: high concentration to low)
What is facilitated diffusion?
The same process as general diffusion, but transport proteins of some kind are needed to help the solute move across the membrane.
What is are some key differences between simple diffusion and simple facilitated diffusion?
(There are three)
1) Specificity: The solute has to fit into the transport protein
2) Competition: Different solutes may fit into the same protein, so they may compete for that space
3) Saturability: Once all protein carriers are engaged, the max rate of diffusion is achieved. Simple diffusion has no max diffusion rate
Does facilitated diffusion require energy?
(Is it an active or passive process?
Facilitated diffusion is still a passive process. No energy, in terms of ATP, are used to enable its action
What is Primary Active Transport?
A transport protein pumps a solute against its energy gradient.
How is primary active transport different than facilitated diffusion?
1) PAT requires energy
2) PAT pumps solutes against their gradient, facilitated diffusion allows for their movement down their gradient
What is Secondary Active Transport?
A combination of facilitated diffusion and active transport.
One solute moves down its gradient using a transport protein, and this same protein uses the energy released from that process to pump another solute against its gradient.
What are the relative concentrations of the following solutes inside and outside of the typical cell?
Organic Anions (A-)
K: Low outside the cell, high in
Na: High outside the cell, low in
Cl: High outside the cell, low in
A: Almost none outside the cell, a LOT in the cell
How permeable is the typical cell to:
Organic Anions (A)
K: High permeability
Na: Low permeability
Cl: Very high permeability
How does water and water solubles solutes move into the cell if its bilipid layer is impermeable to water?
There are channels or pores in the cell that are filled with water, allowing for solute and water movement into and out of the cell
Is an actual cell (in general) permeable, impermeable, or semipermeable to ions?
What are ion leakage channels, and what important role do they play in cells like neurons?
Ion leakage channels are pores in the cell membrane that exhibit selective permeability, allowing ONLY specific ions to pass.
These channels are responsible for the setting the resting potential of neurons
Are leakage channels gated?
No, they are always open
What types of gated channels are there?
Ligand gated (or transmitter gated)
In the cell, how is permeability related to an ion's conductance?
The permeability of a cell to an ion is what establishes that ion's conductance
Define the term equilibrium potential.
The equilibrium potential refers to the electrochemical potential at equilibrium of a particular ion, as calculated by the Nernst equation
Define the term resting potential.
The resting potential refers to the weighted average based upon membrane permeabilities of all the equilibrium potentials of the various ions in a given cell, as calculated by the Goldman equation.
Compare the states of equilibrium and steady state in a cell.
The cell is in equilibrium once ion concentration and the electrochemical gradient is balanced inside and outside of the cell. However, the sodium potassium pump prevents the cell from going into complete equilibrium and maintains the Na+ and K+ ion concentration such that the inside of the cell is -90 mV.
The resting potential of cells changes based upon which cell you are observing
What is the membrane potential of a resting cell?
It will almost always be negative, though there are a few exceptions.
Why is the Nernst equation important for measuring membrane potential?
The Nernst equation takes an ion concentration and converts it to electric potential, allowing us to measure the membrane potential through ion concentrations.
How do we know which direction an ion will move if given a chance across a cell membrane?
Ions will move across a membrane in order to move the cell's membrane potential towards the ion's equilibrium potential
Ex: K+ eq. potential = -97 mV, so it leaves the cell to make the cell more negative
Na+ eq. potential = +66 mV, so it enters the cell to make it more positive
What effect will increasing the conductance of an ion have on the membrane potential?
Increasing the conductance of an ion will give it more weight in determining the cell's membrane potential, so the cell's membrane potential will move towards that ion's equilibrium potential.
What is the equation that gives us the current (movement) of an ion across a membrane?
Ix = gx(Em-Ex)
Ix = current of ion X
g = conductance
Em = membrane potential
Ex = ion potential
(Em-Ex) is known as the "driving force"
What is cell hyperpolarization?
Making the cell's membrane potential more negative.
What is depolarization?
Making the cell's membrane potential more positive
How may we change a cell's membrane potential?
We may hyperpolarize or depolarize a cell by changing its permeability to an ion(s).
How does the concentration gradient change during a cell's depolarization or hyperpolarization?
Typically, the concentration gradient does not change much at all, since the movement of so few ions are needed to change the electric potential.
What are some ways we can artificially change a membrane's potential?
1) Change ion concentrations
2) injecting current into a cell via an electrode
3) Using drugs to alter the membrane's permeability
How depolarized and hyperpolarized can a cell become (if ion conductance were to become infinite)?
The max is the ion's equilibrium potential for each side, so:
EK = -97 mV (max hyperpolarization)
ENa = +66 mV (max depolarization)
What is the importance of the Goldman Equation?
It calculates the membrane potential based on the permeability of the cell to various ions (typically, Na, K, and Cl)
What is the role of the Na/K ATPase pump in maintining membrane potential?
Because of the presence of Na and K leak channels, Na and K would attempt to reach their own equilibrium potentials rather than the potentials they reach in a normal cell. The Na/K ATPase pump pumps Na out of the cell as it leaks in, and recaptures K as it leaks out of the cell.
How much Na and K does the Na/K ATPase pump pump for each ATP?
The Na/K ATPase pump is an example of which kind of transport?
Primary Active Transport
Bonus: What is an example of Secondary Active Transport?