Lecture 3: Membrane Potential Flashcards
membrane potential
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
Negative inside and positive outside?
-intracellular fluid at edge of membrane has excess -ve charge RELATIVE to outside/deficient +ve charge relative to outside
Importance of M.P.
- 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
Potential Energy
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
Differences of Pot. Energy of any solute across membrane…
only differences are electrical charge and concentration of solute
When there is no net movement across a membrane the value of both equations uout-uins and uins-uout are…
the value of both equations is 0
If the substance is not an ion, value of z of the equation for elec-chem pot is…
the value of z is 0; no electrical potential, only concentration
elec-chem PE difference and G(change in free energy)
uins-uout=Goutside to inside
uout-uins=Ginside to outside
-change in free energy moves oppositely to the electrochemical gradient
G0=not spontaneous
Prof.’s method to solve problems: remember 3 things
Remember 3 things:
- u(X)=uins(X)-uout(X); u(X)=[RT ln([X]ins/[X]out)]+[zFVm]
- molecules move spontaneously from state of high potential energy to state of low potential energy (passive transport)
- if a molecule is moving from a state of low PE to high PE it is using an outside energy source (active transport)
Prof’s method to solve problems: Calculate u(X) and look at u(X)’s sign
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.
units for u and G
joules/mol or cal/mol
R is the gas constant, the value and unit are…
R=8.315/K*mol
F is Faraday’s constant, value is…
F=96,485 joules/volt*mol
T=temperature in kelvin
celsius to kelvin=C+273.15
What is Z?
z is the valence of the ion