NPB101: Membrane Potentials Part 2

Membrane Potentials

Membrane Potential implies that theres a voltage _____ between the extracellular fluid and the intracellular fluid

difference

• bc there is a different in electrical charge between the inside and outside of a cell

T/F: the cell recycles/tosses the cells when they die

False, that would be energetically unfavorable because they actually regenerate the cells with energy

Electromotive Force (EMF) ____ a electrical current

drives

T/F: If the voltage goes to zero there is no current 

True If the voltage goes to zero there is current 

Two chambers are separated by a membrane permeable only to Na+. Which of the following will occur? Explain.

a) Na + flows from right to left

b) As Na + flows, a negative charge builds up in the left chamber

c) Cl - flows in the same direction as Na +

d) Na + flows until its concentration is IDENTICAL in both chambers

e) As Na + flows from Chamber 1 to 2, K + flows from 2 to 1

b) As Na + flows, a negative charge builds up in the left chamber, this occurs because this channel is only permeable to Na+ not Cl- or K+ ONLY Na+ so therefore only Na+ can go out which is from left to right and it leaves Cl- behind so that leaves a negative charge in compartment 1 (left)

What kind of gradient is this?

Concentration gradient

How do you generate an electrical motive force?

voltage membrane potential in real cells by getting ion flux to occur, that’s how its established

Explain this Concentration Gradient

1. First K+ flows to chamber #1 down its concentration gradient

2. As K+ flows, a positive charge builds up in chamber #1

3. Then a positive charge in Chamber #1 is strong enough that it repels K+ flux from Chamber #2—>Chamber #1

4. So it then becomes balanced (equal in magnitude) and generates an electrical motive force

When Equilibrium is reached forces are ____.

balanced

When Equilibrium is reached F_{___}= F_{___}

conc, elec; (Concentration gradient is equal in magnitude due to the force cause by the electrical gradient )

T/F: The Concentration gradient equals the electrical gradient when equilibrium is reached?

True, the Concentration gradient equals the electrical gradient when equilibrium is reached

What equation is this?

The Nernst Equation

The Nernst Equation predicts the ____ at equilibrium.

potential

Permeability is how ___ it is for an ion to cross

easy

T/F: In living cells, ions are unequally distributed

True, in living cells ions are unequally distributed, this can be due to selective permeability

T/F: the membrane does not exhibit differences in ion permeability in Living Cells?

False, in living cells the membrane does exhibit differences in ion permeability

T/F: The interior of a Living cell is more electronegative?

True, the interior of a living cell is more electronegative, this can be because of unequal distribution of ions

What equation is this?

the GHK (Goldman-Hodgkin-Katz) equation

What does the GHK equation calculate?

The GHK equation calculates the resting membrane potential of real cells