VL 11 (Salvo Chiantia)

Question 1

Membrane structure - Fluid mosaic model

Answer 1

Phospholipids – phosphate and fatty acid tails
–-> Hydrophilic phosphates
–-> Hydrophobic fatty acid tails
Two layers
–-> With tails together
Protein
–-> Embedded throughout - integral
–-> Some just surface – peripheral
–-> Motility

Question 2

Membrane dynamics

Answer 2

• Cholesterol molecules prevent membrane from becoming too rigid
• Proteins and lipids diffuse along surface
• Proteins are anchored by fibers in the
  cytoskeleton
• Phospholipids can even flip flop
• Membranes can fuse

Question 3

Structure of a building block of a cell membrane

Answer 3

Question 4

What are the building blocks of cell membrane

Answer 4

Question 5

Structure of Fatty acids

Answer 5

• long hydrocarbon chains
• various lengths

Saturated fatty acids
* no double bonds

Unsaturated fatty acids
* 1 or more double bonds
–> Cis: cis-Δ9 →DB between C(9) + C(10)
–> Trans: trans-Δ2→DB between C(2) + C(3)
* w-3 counting from distal end (it means that the first double bond is located three carbon atoms away from the distal end (the end farthest from the carboxyl group) of the fatty acid chain)

Question 6

Stucture of Glycerophospholipids in particular Plasmalogen and Phosphatide

Answer 6

• Glycerol backbone
• 2 fatty acids usually 1 staurated and 1 unsaturated
• C-3 carbon has phosphoric acid group

2 Types of Glycerophospholipids
1. Plasmogen
2. Phosphatide
–> Phosphatidylethanolamines
–> Phosphatidyserines
–> Phosphatidylcholines
–> Phosphatidylinositol
–> Diphosphatidylglycerol (cardiolipin)

Question 7

Structure of the diffrent Types of Phospholipds

Answer 7

• Phosphatidylethanolamines
• Phosphatidyserines
• Phosphatidylcholines
• Phosphatidylinositol
• Diphosphatidylglycerol (cardiolipin)

Question 8

Limits of the fluid mosaic model

Answer 8

• trans-leaflet asymmetry
• lipid-protein domains
  –> Example: Studies on virus envelopes
• uses plasma membrane of host cell as own cell
• specific subset of lipids + proteins in virus envelope
• virus budd from specific host cell regions
• lipid-protein domains = specific host cell regions, which interact with viruses = raft domains
  (with cholesterol, sphingomyelin, glycosphingolipids, GPI-anchored proteins)

Question 9

Driving force for domain formation

Answer 9

diffusional order:
decreased lateral movement
structural order:
same side chains;
unstructural order:
cis side chains

condition:
1.) Gel phase
* T<Tm
* cis→trans isomerization→strong VdW (high structural + diffusional order)→stable system
* packed→decreased lateral movement
* thicker, stiffer membrane

2.) liquid disordered
* T>Tm
* high fluid
* irregular packing
* trans
* cis→reduced accessible surface area to other fatty acid chains→weakend VdW

3.) liquid ordered
* high, rigid sterole→tighter packing + separating gel phase lipids
* all-trans (energy min. configuration)
* rapid lateral diffusion

Question 10

Control of Membrane fluid

Answer 10

• Processes require some fluidity
• Tm = melitng temperature depends on length of fatty acid chain
• Double bonds increase fluidity
• Cholesterol insters into bilayers and disturpts interactions, moderates fluidity

Question 11

Trans-leaflet asymmetry

Answer 11

Trans-leaflet asymmetry (= difference in lipid composition)

Outer leaflet
* lipids: saturated, mostly uncharged

Inner leaflet
* lipids: unsaturated, charged
* net charge: -
* surface potential (-25 mV) attract, binds +-charged molecules

flippase, scramblase
* Ca2+-dependent
* flippase: lipid transport molecule for e.g. PS
* scramblase: randomizes lipid distribution

PS
→greater membrane mechanical stability through interactions with cytoskeletal proteins
* neg. membrane curvature

apoptosis
→decreased entropy
→thermodynamicall equilibrium
* flippase, scramblase doesn ́t work→membrane composition changes
* PS→outer leaflet→recognised by macrophage→scavenges (beseitigt) dying cell