Lecture 3: Membrane Potential

Question 1

membrane potential

Answer 1

the difference in electrical charges btw two points such as inside of the cell and the outside solution

• aka Em or Vm
• Vm=Potential measured inside-pot. measured outside=In-Out

Question 2

Negative inside and positive outside?

Answer 2

-intracellular fluid at edge of membrane has excess -ve charge RELATIVE to outside/deficient +ve charge relative to outside

Question 3

Importance of M.P.

Answer 3

• provides potential energy (form of elec-chem gradient) that can drive transport across membrane
• thus involved in passive & facilitated diffusion, and secondary active transport
• changes in MP can act as a signal, such as in neurons

Question 4

Potential Energy

Answer 4

stored/inactive that has the potential to do work, but is not currently doing so
-all objects left on their own will move from a state of high potential energy to low potential energy

Question 5

Differences of Pot. Energy of any solute across membrane…

Answer 5

only differences are electrical charge and concentration of solute

Question 6

When there is no net movement across a membrane the value of both equations uout-uins and uins-uout are…

Answer 6

the value of both equations is 0

Question 7

If the substance is not an ion, value of z of the equation for elec-chem pot is…

Answer 7

the value of z is 0; no electrical potential, only concentration

Question 8

elec-chem PE difference and G(change in free energy)

Answer 8

uins-uout=Goutside to inside
uout-uins=Ginside to outside
-change in free energy moves oppositely to the electrochemical gradient
G0=not spontaneous

Question 9

Prof.’s method to solve problems: remember 3 things

Answer 9

Remember 3 things:

1. u(X)=uins(X)-uout(X); u(X)=[RT ln([X]ins/[X]out)]+[zFVm]
2. molecules move spontaneously from state of high potential energy to state of low potential energy (passive transport)
3. if a molecule is moving from a state of low PE to high PE it is using an outside energy source (active transport)

Question 10

Prof’s method to solve problems: Calculate u(X) and look at u(X)’s sign

Answer 10

if u(X)0, uins(X)-uout(X) is POSITIVE
and movement from in to out is spontaneous (passive) and movement out to in requires A.T.

Question 11

units for u and G

Answer 11

joules/mol or cal/mol

Question 12

R is the gas constant, the value and unit are…

Answer 12

R=8.315/K*mol

Question 13

F is Faraday’s constant, value is…

Answer 13

F=96,485 joules/volt*mol

Question 14

T=temperature in kelvin

Answer 14

celsius to kelvin=C+273.15

Question 15

What is Z?

Answer 15

z is the valence of the ion

Question 16

Vins-Vout is the membrane potential, what is the unit for Vm

Answer 16

Vm is in volts