Cell Membrane Flashcards
What is a lipid raft?
A subdomain of the PM that contains high []s of cholesterol and glycoSPHINGOlipids - exist as distinct liquid ordered regions of membrane and resistant to extraction with detergents.
How do liquid disordered and solid ordered differ?
Lipid tails with cis conformations - less efficient packing vs trans tails with high order.
High lipid lateral diffusion vs low diffusion.
Thinner bilayer vs thicker.
What type of lipids are preferred in Ld, So and Lo phases?
Ld - glycerophospholipids with unsaturated tails.
So - sphingomyelin (long, saturated HC tails)
Lo - sphingolipids with variable headgroups, cholesterol.
Outline the Lo phase.
lipid raft phase
high lateral lipid mobility
thicker
high lipid tail order.
Which molecules are found at particularly high []s in lipid rafts?
Phospholipids with 2 saturated tails (DPPC)
Palmitoylated proteins
Proteins with longer TM domains
Sphingolipids.
(Those packing efficiently into ordered phase!)
Give five reasons as to why there is a lack of in vivo evidence regarding lipid rafts?
Similar morphology
Small size
Transience (close to critical point)
Other processes.
Outline the picket fence model.
cytoskeletal filaments form barriers, obstructing free diffusion of proteins.
Barriers partition membrane into small domains or corrals - can be transient or permanent.
Outline the lipid shell model.
Actin skeleton & TM domains can INDUCE formation of ordered phase domains in membrane –> merges picket fence & lipid raft models.
Ordered lipids in 1-2 thick layer around TM proteins.
How does lipid shell contrast raft model?
Density of proteins so high, half membrane in ordered phase so ‘sea’ in this case is minority.
how can proteins help modulate membrane fluidity?
change spontaneous curvature of membrane
insert into either leaflet controlling curvature direction.
regulated so can rapidly change membrane curvature.
Act as lipids with high spontaneous curvature.
Caveolin and flotilins
What does the Nernst equation outline?
outside of membrane has positive chargen, inside is negative (RMP = -60)
RMP generates membrane electrical field as THIN membrane.
electric field counterbalances ion diffusion through channels.
When electric field exact to balances diffusion –> no net ion movement
membrane impedes diffusion of ions and is thin so acts as capacitator.
what evidence is there so far for the lipid raft hypothesis?
Co-existing phases can be produced in artificial membranes.
Lipidomics (NMR) - PM composition close to critical point.
Drugs - treat cells with mthyl-b-cyclodexyrin & find detergent resistance and faster diffusion (cholesterol removed).
DRM - triton-X-100 shows fraction of membrane are insoluble like artificial ordered phases.
What are the melting temperatures of DOPC and DPPC?
1 degree (18:1) 55 degrees (16:0)
What is the MSD?
4DT doe 2D
Absolute distance from origin
