VL 12 (Salvo Chiantia)

Question 1

Where are Proteins according to fluid mosaic model?

Answer 1

Membarne Proteins are extrinsic or intrinsic

Extrinsic/peripheral proteins
* e.g: Cyt c, MBP, Annexins, Influenza M1
* interact with surface, intrinsic proteins

intrinsic proteins (completely embedded into bilayer)
* monotopic, bitopic type I/II, polytopic
–> monotopic: similar to extrinsic proteins
–> bitopic: two parts outside membrane (= ectodomain); one part spans the membrane; type I/II: N/C-terminus in-/outside the cell
–> polytopic: > two parts outside membrane; helical bundles (e.g. Bacteriorhodopsin) or β-barrels
* proteins cross via α-helices/β-strand
* hydrophobic domain interacts with hydrophobic fatty acids of inner leaflet
* amphiphile

Question 2

Explain passive transport

Answer 2

Diffusion
– Tendency of molecules to spread out into the available space.
Substances will diffuse down their concentration gradient.
(Entropy)
Osmosis
– The diffusion of water molecules across a selectively permeable
membrane.
Facilitated Diffusion
– Transport proteins are helping molecules to cross membrane,
but still diffusion (lowering overall free energy) thus doesn’t
require energy from cell.
– Channels/pores → selectivity

Question 3

Explain active transport?

Answer 3

• Movement of solutes, against their
  concentration gradient, with the help of
  transport proteins.
• Requires cell to expend energy
• Solute becomes more concentrated in a particular area.

Example is Sodium-Potassium Pump. (Na-K)

Question 4

Model membranes

Answer 4

Cellulare membranes are complex, they have specific Protein-Lipid and lipid-lipid interactions.

To study:
* membrane proteins reconstituted in an hydrophobic environmemt (similar to the plasma membrane)
Example:
* Micelle
* Liposome (e.g spectroscopy or caliometry)
–> to study drug delivery, nanomedicine
* Giant unilamellar Vesicles
–> study any possible lipid composition
–> Proteins can be included
–> Fluorescent lipids can be used to visualize diffrent lipid phases
* Blebs, Giants plasma membrane vesicles
–> Giant GUVS
–> Compromise between plasma
membrane and GUVs

Question 5

Explain protein-induced membrane remodelling

Answer 5

a) specific lipids → specific membrane shape
b) integral proteins with intrinsic curvatur→curvature on oligomerization
(e.g. large extracellular part→coned shape formed)
c) cytoskeletal polymerization, tubules pulling by motor proteins
d) indirect: proteins bind one side of bilayer; direct: protein binds
membrane directly (not bilayer)
e) amphiphatic helix inserted; one leaflet→lipids pushed away→larger
membrane leaflet

Question 6

Influenza Virus Membrane

Answer 6

• assembly, budding in lipid raft domains on apical membrane of infected cells
• hemagglutinin (HA), neuraminidase (NA) are part of lipid rafts→coalescence, enlargement of raft domains
• HA, NA clustering→membrane deformation, initiate virus budding, alter membrane curvature
• M1
  –> bind cytoplasmic HA-,NA-tails → M1 polymerizes → interior virion structure
  –> docking site for viral RNPs
  –> mediate M2 recruitment
• M2
  –> in cholesterol-rich environment: stabilizes budding site
  –> budding virion neck: alters membrane curvature through insertion of amphiphatic helix→ membrane scission, virion release