Electrochemistry

Question 1

By the law of electroneutrality, if the intracellular conc. of + charges is 6 mM what should the conc. of - charge be?

Answer 1

6 mM

Question 2

What does it mean to be at an electrochemical equilibrium state?

Answer 2

Force due to charge separation = force due to conc. gradient

Question 3

What is the intracellular concentration of K+ in a normal cell?

Answer 3

120 mM

Question 4

What is the extracellular concentration of K+ in a normal cell?

Answer 4

4 mM

Question 5

What is the nernst equation?

Answer 5

v = RT/zF ln (Cout/Cin)

v = potential
R= const. 
F = const.
T = temp.
z = signed charge of ion
C = concentration

Question 6

When using the nernst equation what does solving for v tell you?

Answer 6

The point at which EP = CP

Question 7

What does decreasing the conc. gradient of potassium do?

Answer 7

reduces the voltage across the cell

Question 8

What if Kin = Kout?

Answer 8

no membrane potential

Question 9

In a normal cell the intracellular conc. of potassium is 120 mM, while extracellular is 4 mM. This generates a membrane potential of -88 mV. What is the chemical potential?

Answer 9

+88 mV, electrical and chemical potentials must be equal and opposite

Question 10

What is the difference in Equilibrium and Steady State?

Answer 10

in both there is no net change in ion conc. but

-in steady state ATP is used to be sure certain concentrations are maintained

Question 11

What would happen over time if Na+/K+ ATPase stopped working?

Answer 11

Na+ would leak in down its conc. gradient

K+ would leak out down its conc. gradient

Question 12

What is the typical intracellular conc. of sodium?

Answer 12

14 mM

Question 13

What is the typical extracellular conc. of sodium?

Answer 13

140 mM

Question 14

T or F: different cell types have different Vm

Answer 14

True

Question 15

What does the GHK equation take into account?

Answer 15

1. concentration gradient across membrane

2. Relative permeability (P) of membrane to ions

Question 16

What is the relative permeability (Pk) of potassium at rest?

Answer 16

95% - postassium = MUCH MORE PERMEABLE

Question 17

What is the relative permeability (PNa) of sodium at rest?

Answer 17

5%

Question 18

T or F: GHK and Nernst eqns. always tell you the charge on the inside relative to outside?

Answer 18

True

Question 19

What does a resting potential of ~90 mV compared to 60 mV in normal cells suggest?

Answer 19

That K+ is probably even more permeable in cardiac tissue and that different tissues may have different permeabilities

Question 20

What is the major determining factor of membrane potential?

Answer 20

Potassium

Question 21

When is hyperkalemia observed?

Answer 21

kidney disease - lots of extracellular potassium

Question 22

What is true of the cell in hyperkalemia?

Answer 22

it is depolarized (more positive)

Question 23

What is true of hypokalemia?

Answer 23

Low extracellular conc. of K (cell = hyperpolarized)

Question 24

When might hypokalemia be observed?

Answer 24

vomitting and disease over a long period

Question 25

T or F: small variations (±1 mM) of K+ can kill you?

Answer 25

True

Question 26

If Vk ≠ Vm what is true?

Answer 26

There will be a net movement of ion

Question 27

What is the net driving force on a cell equal to?

Answer 27

Vm - Vk

Question 28

In real life the driving force of the electrochemical gradient pushes potassium out because Vm = -60 mV and Vk = -88 mV, what prevents potassium from being driven out?

Answer 28

Na+/K+ ATPase

Question 29

T or F: its necessary to worry about the electochemical gradient for an amino acid?

Answer 29

False, only have to worry about chemical gradient

Question 30

T or F: graded potentials occur over long distances?

Answer 30

False, Graded potentials occur over short distances while action potentials occur over long distances