3.1 Membrane Permeability Flashcards
What is a semi-permeable membrane?
A layer through which only allowed substances can pass.
What is the permeability coefficient? What does it depend on?
Measure of time taken to pass through the membrane
E.g. H2O 10^-2 (very quick), Na+ 10^-14 (very slow)
Depends on what membrane you are measuring for e.g. Erythrocyte vs axon.
Give some examples of roles of transport
- Maintain ionic concentration
- Maintain intracellular pH
- Regulate cell volume
- Concentration metabolic fuels/building blocks
- Concentration products/toxins
- Generation of ion gradients = needed for electrical excitability
What is a ping-pong transport protein?
Moves one molecule per protein at any one time
How does a channel by facilitated diffusion work?
- High conc to low conc
- Carrier protein (gate fully opens allows lots of moles through)
- Passive (no energy required)
- Large and charged molecules (glucose, ions)
What is simple diffusion?
- Movement from high conc to low conc gradient
- No carrier protein
- Passive (no energy)
- Very small (O2) and lipid soluble molecules (Steroids)
How does an ion channel by facilitated diffusion work?
- Ligand gated
- high conc to low conc
- carrier proteins
- Ligand binds, channel opens/closes and ions go through - Voltage gated
- membrane depolarisation (one side more positive than other) causes channel to open
What is active transport?
- Transport of ions/mols against unfavourable concentration/electrical gradient
- Energy required
What is passive transport?
- Occurs spontaneously either through lipid bilayer/proteins along concentration gradient
- No energy required
Intracellular and extracellular values of Chlorine?
Intra - 4.2mM
Extra - 123mM
Intracellular and extracellular values of sodium?
Intra - 12mM
Extra - 145mM
Intracellular and extracellular values of Calcium?
Intra - 10^-7M
Extra - 1.0-1.5mM
Intracellular and extracellular values of potassium?
Intra - 155mM
Extra - 4mM
What is the difference between primary and secondary active transport?
Primary - Energy derived directly from breakdown of ATP
Secondary - Energy derived secondarily from energy that has been stored in the form of an ionic concentration difference between two sides of the membrane
What is the difference between uni transport and co transport?
- Uniport - Only one mol transported at a time
E.g proton pump in mitochondria - Co transport
- Symport - 2 solutes moving in same direction
- antiport - 2 solutes moving in opposite directions
E.g. Na+/glucose cotransporter - 2 sodiums and 1 glucose move into cytoplasmic space
What is the osmosis?
Movement of water across semi permeable membrane from region of low solute concentration to region of higher solute concentration ‘
Passive transport
No energy required
What is Ca2+ ATPase and its function?
- Primary active transport
- UNIPORT
- Exclude Ca2+ ions
- Requires ATP
- High affinity, low capacity
What is Na+ Ca2+ exchanger
- Secondary active transport (as driven by extracellular Na+ conc)
- ANTIPORT (cotransport)
- 3Na+ in, 1 Ca2+ out
- Low affinity, high capacity
What is the sodium pump and its function?
- Na+ K+ ATPase
- Active transport as uses ATP
- Antiport
- 3 Na+ out and 2K+ in maintaining normal concentration gradient
- High K+ inside as responsible for resting membrane potential (-70mV)
Na+H+ exchanger and its function?
- ANTIPORT
- 3 Na+ pump out from Na+K+ATPase, one Na+ pumped back in through Na+H+ exchanger, pumping out one H+ too.
Na+Glucose co-transport and its function?
- Entry of two Na+ provides energy for entry of 1 glucose molecules against concentration gradient
- Symport - co transport
- E.g. Small intestine/kidney
F1F0 ATPase and function?
Active transport in reverse mode
Generates ATP in cell
What is an aqua porin?
Water channel
Give two clinical examples where there is a problem with a pump?
In cystic fibrosis patients, CFTR not present in apical membrane of epithelial cells.
Therefore chloride ion transport across membrane compromised
Water does not follow to hydrate secreted mucus causing it to become viscous and cause infection
Vibrio Cholera Protein Kinase A effects CFTR Too much chlorine leaves Too much water follows out Causes diarrhoea and dehydration
Give an example of a drug effecting
- Fluoxetine (antidepressant)
- Outward flow of K+ down concentration gradient
- Leads to uptake of serotonin in presynaptic cleft and by platelets with Na+ ion
- Fluoxetine inhibits SERT (serotonin reuptake transporter) so NT stays in cleft for longer!
