Session 3: Membrane Permiability Flashcards
What is a semi-permisible membrane?
A layer through which only allowed substances can pass
What types of molecules can pass a phospholipid bilayer?
- hydrophobic
- small, uncharged, polar molecules
What types of molecules cannot pass a phospholipid bilayer?
- large, uncharged, polar molecules
- ions
Give an example of a molecule which can pass a phospholipid bilayer.
- oxygen
- carbon dioxide
- water
- urea
- glycerol
- benzene
- nitrogen
Give an example of a molecule which cannot pass a phospholipid bilayer.
- glucose
- sucrose
- protons
TRUE OR FALSE: molecules with a small permeability coefficient have a high permeability.
False: molecules like Na+ have a very low permeability coefficient (10^-2) and is hardly permeable
What two factors influence passive transport?
- Permeability
2. Concentration gradient
TRUE OR FALSE: rate of passive transport doesn’t increase linearly with increasing concentration gradient
False
Give 3 reasons why transport processes are so important.
- Maintenance of intracellular pH
- Regulation of cell volume
- Maintenance if ionic composition
- Expulsion of metabolic waste and toxic substances
- Generation of ion gradients necessary for AP
Why is a rotating carrier or reciprocating carrier (flip-flop) not considered the correct model for transport proteins.
Thermodynamically unlikely
What does it mean if +deltaG is positive?
It’s active transport
What does it mean if -deltaG is negative?
Passive
Define active transport.
Allows the transportation of ions or molecules against an unforgivable concentration gradient. Required energy (either directly or indirectly from ATP)
Is there more sodium ions inside or outside the cell?
Outside
Is there more chloride ions inside or outside the cell?
Outside
Is there more calcium ions inside or outside the cell?
Outside
Is there more potassium ions inside or outside the cell?
Inside
What is a primary transporter?
Uses ATP directly
What is a secondary transporter?
Uses energy from ATP indirectly e.g. NCX
Give an example of a primary active transporter.
Calcium ATPase (PMCA)
Define unimport.
Movement of one molecule
Define symport.
Co-transport. Movement of 2 molecules in the same direction.
Define antiport.
Co-transport. Movement of 2 molecules in different directions.
Give an example of an antiport transporter.
NXC
Which ions and how many move using an NXC transporter?
3 sodium ions move out of the cell, 2 potassium ions move into the cell
What transporter is important for creating a high intracellular potassium concentration?
- MAINLY membrane permeability for potassium ions
- secondary: sodium pump however this only generates 5-10 mV through electrogenic pump activity
