Phys-Pharm

Question 1

Cell Membrane Composition (by weight)

Answer 1

42% lipids
55% proteins
3% carbohydrates

Question 2

Intracellular Concentrations of Ions

Answer 2

K+ 140mM
Na+ 5-15mM
Cl- 4mM
Ca2+ 0.0001mM

Question 3

Extracellular Concentrations of Ions

Answer 3

K+ 5mM
Na+ 145mM
Cl- 110mM
Ca2+ 2.5-5mM

Question 4

transport across the membrane

Answer 4

diffusion (lipid soluble molecules)
transport via transport molecules (small molecules + ions)
endocytosis (large molecules)

Question 5

Active vs Passive Transport

Answer 5

Active transport uses ATP directly (sets up gradients)

Passive Transport uses ATP indirectly (uses gradients set up by Active transport)

Question 6

Active Transport

Answer 6

ATPases and Pumps
LOW TURNOVER (<100/sec)

Question 7

Na+/K+ ATPase

Answer 7

Na+/K+ Pump
ubiquitous
tetramer (2 alpha-, 2 beta- subunits)
3 Na+ out of cell, 2 K+ into cell
maintains low intracellular Na+ Conc.
Requires ATP (ATP hydrolysis)

Question 7

Passive Transport

Answer 7

Pores (aquaporin) tend to always be open
Channels (Na+ Channel) allow ions through
Carriers (Sodium Glucose Carrier) allows ions and molecules through via a conformational change

Question 7

Carriers Classification

Answer 7

Uniporters - Move one solute
Symporters (Cotransporter) - Move more than one solute in the same direction
Antiporter (Exchanger) - Move more than one solute in opposite directions

Question 8

Carriers

Answer 8

Facilitated diffusion + electrodiffusion
Turnover = 10^2 to 10^3 /sec
highly selective
can demonstrate saturation

Question 9

Carrier Saturation

Answer 9

When all carriers are moving the maximum number of ions it demonstrates saturation

Question 10

Ion Channels

Answer 10

Set Membrane Potentials
Gated (open gate = conductive and ions flow making a current, closed gate = non conductive and ions don’t flow meaning no current)
HIGH TURNOVER = 10^6 to 10^8 / sec
Na+,Cl-,K+,Ca2+ non-selective

Question 11

Patch Clamp Technique

Answer 11

Measures current from ion channels
2 types
Cell Attached (electrode is sealed onto membrane, looks at ion channel directly)
Whole Cell (electrode is inserted into cell, current is recorded from all ion channels in the cell)

Question 12

Equation for total current in cell

Answer 12

I = N.Po.g(Vm-Ei) . N is number of channels. Po is open probability. g is single channel conductance. Vm is membrane potential. Ei is nernst potential of ion I (equilibrium potential).

Question 13

Membrane Potentials

Answer 13

In all cell membranes
Usually negative
functionally vital - mediated transport of ions

Question 14

Measuring Vm

Answer 14

Measured Intracellularly
Narrow, sharp, glass electrode pushed into cell through membrane
Electrical contact between KCl in electrode measures Vm compared to air outside

Question 15

Contribution of Na+/K+ ATPase to Vm

Answer 15

Contributes 20%

Indirect contribution intracellularly

Question 16

Contribution of K+ Channels

Answer 16

High IC conc, Low EC conc
K+ moves to EC generating -ve Vm
-ve membrane potential brings K+ back into the cell
movement out=movement in - no net flow = no current

Question 17

Equilibrium Potential Equation

Answer 17

Eion=RT/zF x Ln([ion]o/[ion]i)
OR
Eion=61.5/z x log([ion]o/[ion]i)

Eion = equilibrium potential
R = gas constant
T = temp in K
z = valence ion
F = faradays constant

Question 18

Equilibrium Potential

Answer 18

When no net movement of an ion

Vm=/=Eion because there’s multiple channels

Question 19

Contribution of Na+ Channels

Answer 19

High EC conc, low IC conc
+ve membrane potential pushes Na+ out of the cell
movement out = movement in so no current
When balanced = ENa
but Vm=/=ENa because some sodium channels are closed

Question 20

Goldman Equation

Answer 20

Vm=RT/zF x ln(PNa[Na]o+PK[K]o)/(PNa[Na]i+PK[K]i)
or
Vm=61.5/z x log(PNa[Na]o+PK[K]o)/(PNa[Na]i+PK[K]i)

Question 21

Electrogenic Transport

Answer 21

Leads to the translocation of net charge across the membrane.
Change in Vm = Change in permeability

Question 22

Why control intracellular pH

Answer 22

If pH changes, change in protein charges, change in protein conformation, change in function, can be a disaster.

Question 23

Control of intracellular pH

Answer 23

increase [H+] = acidify
compensate by removing H+ (alkalisation)
decrease [H+] = alkalinise
compensate by adding H+ (acidification)

Question 24

Measuring Intracellular pH

Answer 24

insert 2 electrodes into cell,
measure voltage difference
change in voltage is proportional to change in pH (electrodes calibrated with pH standards)
pH=(V-offset)/slope
HARD TO USE IN SMALL CELLS

Question 24

Measuring Intracellular pH

Answer 24

insert 2 electrodes into cell,
measure voltage difference
change in voltage is proportional to change in pH (electrodes calibrated with pH standards)
pH=(V-offset)/slope
HARD TO USE IN SMALL CELLS