Session 5 - Lecture 1 - Membrane Permeability Flashcards
1 - Intro
How molecules cross the plasma membrane
- noncharged molecule
- macromolecule
- H2O
- charged molecules and ions
- plasma membrane
{talk about the proteins you find in membranes and what they do; ATP-dependent ion channels; carrier proteins and clinical relevance}
2 - Aims of this Lecture
Aims of this Lecture
- Define membrane permeability
- Discuss the principles of solute movement across biological membranes
- Distinguish between passive diffusion, facilitated transport and active transport across membranes
- Define the terms uniport, co-transport, symport and antiport
- Relate that information to clinically useful examples
3 - Lecture Structure
Lecture Structure
• What is a semi-permeable membrane?
• What types of molecules can permeate a lipid bilayer?
• How do proteins contribute to membrane permeability?
– Transporters (this lecture)
– Channels (mainly the next lecture)
• Where does the energy come from for membrane transport?
• What has all this got to do with medicine?
{these qs might come up in SAQ (except 5)!
- permeate/penetrate
3b. also next week’s lecture - energy to supply MT processes}
4 - What is a semi-permeable membrane?
What is a semi-permeable membrane?
• A layer through which only allowed substances can pass
- Lipid bilayer
- Water
- Water
- Polar head (hydrophilic)
- Nonpolar tails (hydrophobic)
- Polar head (hydrophilic)
{Phospholipid - polar head – phosphate part in head and lipid which is usually drawn as a tail – hydrophobic core in middle.
And you will understand that ordinarily that layer is impermeable to water – water cannot pass through that which is what this diagram implies. However, Water is a COMPONENT of PMs – it’s part of the membrane – if you take a membrane and put it on the surface and leave it there – it will dry out – water’s gone, it’s evaporated e.g. chicken skin – 2cmx2cm put it on a plate, kitchen sink – leave it for 3 days, bit smelly – shrunk bc water has evaporated from the tissue.
But the def of a SP membrane is written right here learn this
– analogy which is the electric gate at the front of this building – when you came into this building this morning went through 3 permeable layers – push door, rotate door (cotransporter), electronic gate - you are an allowed substance.
Another door permanently opened between café and foyer – always open, like ion channel – things can pass through that - all transport proteins in the membrane, and you’re the substance getting through those membranes.
In a physiological sense a SP membrane where some substances can pass through bc right size/shape/credentials but other material that does not have the right shape/credentials cannot get through}
5 - Black film
Black film
- Lipid bilayer (membrane)
Experimentally:
Phospatidylserine mixed and spread onto glass or plastic plates with pinhole
Submerged into hydrophilic solution
Appears black because light is reflected back
{First experiments looking at membranes and MP occurred in 1920s and used a black film technique – purified PS mixed onto plate with pinhole in middle of it. PL bilayer separated across pin hole.
Called black film bc if you look at it end on instead of side on reflects all the light so appears black – like pupil of eye appears black not bc it reflects but absorbs light – like black hole – everything goes in, some of it stays, some of it goes back out. Red eye when flashed white light in photos – someone has detached retina – instead of red eye – white eye.}
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