Membrane Permeability Flashcards
Which 2 groups of molecules can diffuse across the phospholipid bilayer?
- Hydrophobic molecules (eg. Oxygen, carbon dioxide, nitrogen)
- Small uncharged polar molecules (eg. H20, urea, glycerol)
(Respiratory gases and water mainly)
Which 2 types of molecules can not diffuse across the phospholipid bilayer?
- Large uncharged polar molecules (eg. Glucose and sucrose)
^ need some kind of aid from a protein - Ions
What does the permeability coefficient show?
How easily a molecule passes across a bilayer
What 2 factors effect the rate of passive transport?
Permeability coefficient and concentration gradient
Does water cross a phospholipid bilayer?
Yes, water has a (relatively) high permeability coefficient
What is band 3?
An anion exchange protein (found in bilayer and allows cl- to be transported across)
What do transport processes in membranes do? (6)
- Maintenance of ionic composition
- Maintenance of pH
- Regulate cell volume
- They concentrate fuels and building blocks into the cell
- Extrude waste/ toxic substances
- Generate ion gradients necessary for electrical excitability
What is the ping-pong model of membrane transport proteins?
The proteins are in an ‘open’ position and the substrates bind to them and cause the proteins to undergo a conformational change which allows the substrate to be released on the other side of the membrane.
What is facilitated diffusion?
It occurs through ion channels that are at rest closed but when high concentrations of their ions accumulate they allow flow of ions down (can pass down a concentration or electrical gradient)
What is a ligand?
A molecule which binds to a receptor and causes a conformational change
Give an example of 2 ligand gated channels?
Ach binding - the acetyl choline binds to the receptor and opens it to allow sodium to pass through
ATP binding - when the amount of ATP is high inside the cell the ATP binds to the receptor and closes the gate and k+ no longer passes through
How do voltage gated channels work?
There is a voltage sensor inside the gate and as the voltage inside changes it can cause repulsion to the voltage sensor. This cause the sensor to move up (and sometimes out as well) which opens the receptor gate.
What do the facilitated transport processes do?
They increase the maximum velocity of diffusion
Where does energy come from in passive transport?
The concentration gradient
Will passive transport discharge or charge the membrane?
It will discharge as it goes in the direction of the electrical potential
What is active transport?
It allows the transport of ions or molecules against the concentration or electrical gradient (either directly or indirectly energy comes from ATP)
What percentage of ATP is used for active transport?
~50%
What are the normal concentrations of Na+ inside and outside the cell?
Out - 145mM
In - 12mM
What are the normal concentrations of K+ inside and outside the cell?
Out - 4mM
In - 155mM
What are the normal concentrations of Ca+ inside and outside the cell?
Out - 1.5mM
In - 1x10-7mM
What are the normal concentrations of Cl- inside and outside the cell?
Out - 123mM
In - 4.2mM
What is a primary active trasnporter?
It takes ATP directly to the active site of the protein and hydrolysis it to ADP whcih causes a conformational change whcih drives Ca+ out.
Give examples of primary active transporters?
Ca+ ATPase transporter
ATP synthetase (discharges protein gradient from inner membrane space of the mitochondria and drives ATP synthesis)
-the gradient is used to drive
What is a co-transporter?
They transport 2 substances across the membrane either in the same direction (symport) or in opposite directions (antiport)