Session 3 (Membrane Permeability + ATP Dependent Pumps And Ion Exchangers) Flashcards
What types of molecules can pass through membranes? (4)
Lipid soluble molecules
Hydrophobic molecules
Small molecules
Non polar molecules
What is the role of a membrane? (6)
Maintain intracellular pH Maintain intracellular ionic composition Regulate cell volume Control uptake and concentrations of metabolic fuels Control extrusion of waste Generate ionic gradients
What do membranes have which allows them to perform many of their functions?
Transport systems (move hydrophilic and charged molecules etc)
What is the permeability coefficient?
The speed with which a molecule transverses across a lipid bilayer (small number=slow movement)
What is another word for water gradient?
Osmotic gradient
Where might you find water channels that move water by facilitated diffusion?
What are these channels called?
Kidneys (collecting duct)
Aquaporins
How can you increase the membranes permeability to polar substances?
Have specific proteins within the bilayer that transport said molecules
What are the 3 models for facilitated transport?
Pore (channel proteins) Ping pong (carrier proteins) Flip flop (not realistic)
Name 3 types of gated channels
Ligand gated
Voltage gated
Gap junction (connexin)
What values for Gibbs free energy change are given for active movement across a membrane?
> 0
What values for Gibbs free energy change are given for passive movement across a membrane?
<0
What types of proteins form simple diffusion?
Channels (pores)
What type of proteins perform facilitated diffusion?
Carriers (ping pong)
What type of transport does a co-transporter do?
Secondary active transport
Why are co-transporters said to do ‘secondary active transport’?
Because an energy source is needed for the movement of molecules but the energy is used indirectly
Give 2 examples of co-transportation and identify, for each, which type of transport it is (ie symport/antiport)?
Na+/glucose (found in kidneys) - symport
NCX - antiport
Na+/H+ - antiport
What are the functions of Na+/K+ ATPase? (5)
Forms Na+/K+ gradients which drive secondary active transport Controls pH Controls cell volume Controls [Ca2+] Controls nutrient uptake
How is acidification of the cell opposed?
Expelling H+ or inward movement of HCO3-
How is alkalisation of the cell opposed?
Expelling HCO3- (by anion exchanger)
What role does Na+k+ATPase play in pH control?
Sets up Na+ gradient which is then utilised by NHE, Na+/H+/HCO3-/Cl- co-transporter and Na+/HCO3- co-transporter
(Effectively all the transporters that move Na+ ions in)
How many molecules of water does every ion take with it as it leaves/enters a cell?
6
What 2 proteins remove residual Ca2+ from the cytosol? Why only residual amounts?
PMCA and SERCA because it has a high affinity but a low capacity
What protein is used to remove most of the Ca2+ from the cytosol? Why can it move a lot?
NCX (sodium calcium exchanger) because it has a low affinity but a high capacity
What protein would be used to oppose a low pH?
NHE (sodium hydrogen exchanger) (Na+ in and H+ out)
