PNB 2274 EXAM 2 QUESTIONS AND ANSWERS
Why are cell membranes not conductive? - CORRECT ANSWER- cell membranes
insulate the flow of electrical charge.
How is the electrical potentials (membrane voltage) measured in a cell? - CORRECT
ANSWER- Membrane voltage is always in terms of inside relative to outside: electrical
potentials are measured using intracellular electrodes inside of cells with reference to
an external ground electrode.
At what point do we get a balance between diffusion and electrical charge? - CORRECT
ANSWER- Nernst equilibrium
- Eionx
- the electrical potential/voltage at which the diffusional flow of an ion one way is
balanced by the electrostatic attraction in the other.
At equilibrium what is the voltage like of a membrane? - CORRECT ANSWER- at
equilibrium there is a difference in charge
What is the Nernst Equation? - CORRECT ANSWER- Eionx = RT/zF ([x]out/[x]in)
What determines the membrane potential at which an ion is in equilibrium? - CORRECT
ANSWER- the concentration gradient and the charge of the ion
(transporters will serve to change concentration slightly and thus effect equilibrium
potential)
What are the only factors of the nernst equation that will change Ex of a particular ion? -
CORRECT ANSWER- temperature and concentration
What is the ln of 1? Why does this matter? - CORRECT ANSWER- the ln of 1 is zero
- if the concentration of the particular ion on both sides of the membrane are equal, this
part of the nernst equation equals one and therefore there is no net flow of the ion and
Ex=0
- because we are considering only one ion, charge will be equal on both sides of the
membrane
- no conc. gradient or electrostatic gradient
What is the ln of a number less than 1? Why does this matter? - CORRECT ANSWER-
the ln of a number less than 1 is a negative number
, - this means that there is a greater concentration of the particular ion inside the cell than
outside
What is the ln of a number greater than 1? Why does this matter? - CORRECT
ANSWER- the ln of a number greater than 1 is a positive number
- this means that there is a greater concentration of the particular ion outside the cell
than inside
What are the Nernst values (Vm) for potassium, chloride, sodium, and calcium? -
CORRECT ANSWER- Ek= -90
Ecl= -70
Ena= +60
Eca= +130
What are the relative concentrations of potassium, sodium, chloride? - CORRECT
ANSWER- K+ is higher inside
Na+ is higher outside
Cl- is higher outside
Why do we use the GHK equation? - CORRECT ANSWER- cell membranes are
permeable to more than one ion at rest
- the Vm therefore is a weighted average of the Ex for each permeable ion
- "z" is now 1
- "P" is a measure of the permeability
Why is the ratio for the permeability of chloride reversed? - CORRECT ANSWER- Cl is
a negative ion
What is the GHK equation like for a resting membrane? - CORRECT ANSWER- the
permeability to sodium is zero in a resting membrane therefore Pna can be eliminated
from the equation
- only K+ and Cl- dictate the membrane potential at rest
- this is why Vm at rest is close to Ek because the membrane is most permeable to
potassium
What is the role of K+ leak channels? - CORRECT ANSWER- K+ leak channels
maintain the resting potential
Why are cell membranes not conductive? - CORRECT ANSWER- cell membranes
insulate the flow of electrical charge.
How is the electrical potentials (membrane voltage) measured in a cell? - CORRECT
ANSWER- Membrane voltage is always in terms of inside relative to outside: electrical
potentials are measured using intracellular electrodes inside of cells with reference to
an external ground electrode.
At what point do we get a balance between diffusion and electrical charge? - CORRECT
ANSWER- Nernst equilibrium
- Eionx
- the electrical potential/voltage at which the diffusional flow of an ion one way is
balanced by the electrostatic attraction in the other.
At equilibrium what is the voltage like of a membrane? - CORRECT ANSWER- at
equilibrium there is a difference in charge
What is the Nernst Equation? - CORRECT ANSWER- Eionx = RT/zF ([x]out/[x]in)
What determines the membrane potential at which an ion is in equilibrium? - CORRECT
ANSWER- the concentration gradient and the charge of the ion
(transporters will serve to change concentration slightly and thus effect equilibrium
potential)
What are the only factors of the nernst equation that will change Ex of a particular ion? -
CORRECT ANSWER- temperature and concentration
What is the ln of 1? Why does this matter? - CORRECT ANSWER- the ln of 1 is zero
- if the concentration of the particular ion on both sides of the membrane are equal, this
part of the nernst equation equals one and therefore there is no net flow of the ion and
Ex=0
- because we are considering only one ion, charge will be equal on both sides of the
membrane
- no conc. gradient or electrostatic gradient
What is the ln of a number less than 1? Why does this matter? - CORRECT ANSWER-
the ln of a number less than 1 is a negative number
, - this means that there is a greater concentration of the particular ion inside the cell than
outside
What is the ln of a number greater than 1? Why does this matter? - CORRECT
ANSWER- the ln of a number greater than 1 is a positive number
- this means that there is a greater concentration of the particular ion outside the cell
than inside
What are the Nernst values (Vm) for potassium, chloride, sodium, and calcium? -
CORRECT ANSWER- Ek= -90
Ecl= -70
Ena= +60
Eca= +130
What are the relative concentrations of potassium, sodium, chloride? - CORRECT
ANSWER- K+ is higher inside
Na+ is higher outside
Cl- is higher outside
Why do we use the GHK equation? - CORRECT ANSWER- cell membranes are
permeable to more than one ion at rest
- the Vm therefore is a weighted average of the Ex for each permeable ion
- "z" is now 1
- "P" is a measure of the permeability
Why is the ratio for the permeability of chloride reversed? - CORRECT ANSWER- Cl is
a negative ion
What is the GHK equation like for a resting membrane? - CORRECT ANSWER- the
permeability to sodium is zero in a resting membrane therefore Pna can be eliminated
from the equation
- only K+ and Cl- dictate the membrane potential at rest
- this is why Vm at rest is close to Ek because the membrane is most permeable to
potassium
What is the role of K+ leak channels? - CORRECT ANSWER- K+ leak channels
maintain the resting potential
