Membrane Permeability Flashcards
What is the permeability coefficient?
measure of time taken to pass through the membrane, H2O = very quick, Na = very slow
dependent on permeability + concs each side
List some of the roles of transport
Maintain ionic conc, intracellular pH, cell vol, conc metabolic fuels/building blocks, conc products/toxins, generate ion gradients = for electrical excitability
What is passive transport?
no energy, occurs spontaneously
What is osmotic gradient and osmosis?
solute gradient
passive, movement of H2O through semi-permeable membrane up solute gradient
What is facilitated diffusion?
- ion channel = movement through specific proteins
ligand-gated ion channels
voltage-gated ion channels - carrier proteins = passive movement
large charged molecules e.g. glucose
Describe active transport
energy directly/indirectly from ATP, against chem/elect gradient: Na K ATPase
Describe secondary active transport
primary energy source is used indirectly
Ca2+ ATPase what is its function?
primary active transporter = 1 Ca2+ out, uses ATP
What is the Na+Ca2+ exchanger?
3Na+ in for 1Ca2+ out
secondary active transporter driven by Na – Antiport, co-transport
Explain the Na+K+ATPase pump
moves 3 Na out, 2 K in to maintain normal conc gradient, high internal K responsible for resting membrane potential (-70mV) antiport
co-transport, active transport
P-type: phosphorylates aspartate = phosphoenzyme
Na+ H+ exchanger what is its function?
1Na+ in for 1H+ out
uses Na pumped out from Na+K+ATPase, pumps back in to pump H+ out
antiport, co-transport
How does the Na+ glucose co-transporter work?
entry of 2Na+ provides energy or entry of 1 glucose
symport, co-transport
F1F0-ATPase what does this pump produce?
active transport in reverse mode = generates ATP by lose of H+ through ATP synthase
Explain what a uniport is
one solute, one side to the other
What is a co-transporter?
one solute movement dependent on another, 2 transported per reaction
Describe co-transporters: Symport
2nd solute same direction
Describe co-transporters: Antiport
2nd solute opposite direction
What is an aquaporin?
H2O channels
What is a gated channel?
Ligand gated ion channel: Ach binding, ATP-sensitive K channels (ATP binding closes channel, in DM) OR Voltage gated ion channel: membrane depolarisation, conformational change, channel opens
Give and explain a clinical example where a pump is not functioning properly
Cystic fibrosis: CFTR Cl channel
Vibrio cholera infection: PKA effects CFTR = major CL lose = major water lose = diarrhoea
Explain ball and chain inactivation.
Model to explain the fast inactivation mechanism of voltage gated ion channels. 3 states: OPEN: conformational change, ions flow through. CLOSED: no ion flow. INACTIVATED: blockage by ball of AA.
How can you tell if transport is active or passive?
Gibbs free energy +ve = active -ve = passive
How many folds larger is extracellular Ca than intracellular?
~10,000
Why can water pass through the phospholipid bilayer easily?
water diffuses across as a gas
Why does glucose pass through the phospholipid bilayer very slowly?
large molecule
What is the difference between a pump and a transporter?
pump = found on plasma membrane
transporter = found in membranes or organelles
