Membrane Structure Flashcards
What is an exoplasmic face?
Faces external environment.
What is a cytosolic face?
Faces cytosol.
What do phosphoglycerides consist of?
Fatty acyl hydrocarbon tail.
Polar group.
State 3 characteristics of phosphoglycerides:
1) amphiphathic
2) 3 carbon glycerol backbone
3) c-c rotation locates tail + head
Name 4 head groups and their charges:
1) choline, no net charge
2) ethanolamine, no net charge
3) inositol, single net positive charge
4) serine, single net positive charge
Describe structure of sphingolipids:
3c backbone analogous to 3c glycerol
Sphingosine aa present at c3
Fatty acid present at c2
State function ot sphingolipids:
Decreases membrane fluidity.
State a sub-group of sphingolipids:
Glycosphingolipids
What is a sterol?
4-ring isoprenoid-based hydrocarbon.
Do sterols contain phosphates?
No, therefore not a phospholipid.
State a characteristic of the structure of cholesterol:
Hydroxyl substituent causing it to be amphipathic.
State function of cholesterol:
Restricts random movement of phospholipid head groups.
State functions of sterols and explain how:
Maintain rigidity - interacting with hydrophobic tails thus immobilising them.
Increases fluidity - if predominantly long chained saturated fatty acids.
What does double carbon bond stereoisomer cause and how does this affect the membrane?
Rigid kink
Reduces flexibility of membrane as unable to package tightly.
State 2 characteristics of c=c stereoisomer configuration:
Not rotatable
Most are cis.
What 3 structures might phospholipids dispersed in solution aggregate into?
Spherical micelles
Liposomes
Phospholipid bilyars
What is the hydrophobic effect?
Observed tendency of non-polar substances to aggregate in an aqueous solution and to be excluded by water.
What does thermal motion permit?
Lipid molecules to rotate freely along axes and diffuse laterally within each leaflet.
What happens when temp. drops below 37°?
Undergo phase transition from fluid to gel-like state. Sale ot diffusion decreases.
How does absence of proteins affect bilayer?
Unable to spontaneously migrate between eatlets as energetic barmier is too high.
Specialised membrane proteins required to flip membrane lipids between leaflets.
Explain FRAP experiment:
Phospholipids containing fluorescent substituents are used.
Fragment of antibody specific to desired protein is tagged with dye.
Allowing rate at which molecules move, as well as, the proportion of laterally mobile molecules to be determined.
What did this study show?
Phospholipids freely mobile over about 0.5 mu m.
Protein rich regions about 1mu m separating lipid-rich regions from eachother.
Lipids can diffuse within regions but not between.
