PPP - Ions and Electrochemical equilibria

Question 1

Methods of recording electrical activity:

Answer 1

Intracellular - Electrode inside cell

Extracellular - Electrode outside cell

Patch Clamping - Electrode sealed to cell surface

Question 2

Potential of membrane:

Answer 2

At rest, inside -ve charge.

When active, cell depolarises and inside +ve.

Question 3

Intracellular:

Answer 3

Membrane seals around pipette when placed inside cell.
Voltage measure.
Can add dye to see whole network of cells and connections.
Large signal seen so large AP. Range of 100mV.

Question 4

Extracellular:

Answer 4

Picks up signal outside cell.
Weak/small signal. e.g. ECG
Range of 0.1mV.

Question 5

Patch Electrode:

Answer 5

Isolate a patch of membrane.
Record current flowing through.
Press pipette against surface of cell and apply light suction.
Can see behaviour of individual ion channels.

Question 6

3 reasons why electrochemical gradient is set up:

Answer 6

1. Pump moves ions against conc gradient.
2. Restricted movement of ions through channels.
3. Membranes can store charge on surface - capacitance.

Question 7

How capacitance occurs:

Answer 7

K and Cl unequal conc.
High conc inside of both ions.
Ion channels opens.
K moves out but still bound to Cl.
Cl can’t go outside as -ve outside so binds to side of membrane with K - capacitance.
Membrane can store charge - shell of charge.

Requires work to separate opposite charges as they are already close in solution.

Question 8

Osmotic work:

Answer 8

Done by conc gradient.
Pump uses energy from ATP hydrolysis to create conc gradient.

Gradient = [C]out/[C]in
of positive ions. For negative ions, it is the other way round.

Bigger the gradient then more work required. Bigger electrical activity across membrane.

Question 9

Electrical work and equilibrium potential:

Answer 9

Electrical work opposes osmotic work.
Electrical work is the work required to pull apart ions (V).

Equilibrium potential:
No net movement of K. Conc gradient pushing K outside and inside is equal.
Electrical force equal to Osmotic force.

Question 10

Nernst Equation:

Answer 10

E=58xlog([C]out/[C]in)

Question 11

Katz equation:

Answer 11

Involved permeability of ions. K is 50 times more permeable than Na.

Vm=58xlog(504 + 140/ 50140 + 10)

Nernst Eqn didn’t include permeability.
Vm=58xlog(4 + 140/ 140 + 10)