Membrane & Lipid Bilayer

Question 1

Is the lipid bilayer static?

Answer 1

No, it is dynamic
- replacement through recycling

Question 2

What is the membrane composition for liver, erythrocyte, myelin and mitochondrial inner membrane?

Answer 2

Liver = 50:50 (lipid to protein)
Erythrocyte = 50:50 (lipid to protein)
Myelin = 80:20 (lipid to protein)
Mitochondrial inner membrane = 25:75 (lipid to protein)

Question 3

What lipid types exists in the membrane?

Answer 3

Glycerolipids
- Phosphatdiyl + R group
- R group = Inositol/Serine (-) OR Choline/Ethanolamine (neutral)
Sphingolipids
Sterols

Question 4

What are the types of fatty acids and their double bonds?

Answer 4

Stearic Acid - 0 double bonds (meats)
Oleic Acid - 1 double bond at 9 (olive oil)
Linoleic Acid - 2 double bonds at 6/9 (omega 6)
Linolenic Acid - 3 double bonds at 3/6/9 (omega 3)

Question 5

What contributes to the fluidity of the membrane?

Answer 5

• unsaturated:saturated
• temperature
• cholesterol content (sweet spot)
• proteins (impede movemement)

Question 6

What is membrane asymmetry?

Answer 6

• at the PM
• glycolipids on cell surface
• choline on outside VS serine on inside

Question 7

What are the 4 types of lipid transport?

Answer 7

• Lateral diffusion
• Vesicular transport
• Monomeric exchange
• Trans-bilayer movement

Question 8

What are the 3 mechanisms of Trans-bilayer Movement?

Answer 8

• Flippase = serine out to in (use ATP)
• Floppase = choline in to out (use ATP)
• Scramblase = inverts choline and serine (uses Ca2+) – cell death signal

Question 9

What are lipid rafts?

Answer 9

• small
• composed of: cholesterol, sphingolipids, phospholipids, specialized proteins
• more ordered

Question 10

What are lipid rafts used for?

Answer 10

Trafficking
Signalling
Endocytosis

Question 11

What is the composition of lipid rafts?

Answer 11

• high cholesterol concentration

Resident Proteins
- Caveolin, Flotillin, GPI-anchored proteins

Non-Resident Signalling Proteins
- G proteins, non-receptor tyrosine kinase

Question 12

What is the function of lipid rafts?

Answer 12

organizing centres – assemble signalling molecules
membrane fluidity – lateral diffusion

Question 13

What are the challenges of lipid rafts?

Answer 13

• limited methods
• difficult to study in cells
• too small for light microscopy

Question 14

What are the types of lipid rafts?

Answer 14

Caveolae – invagination of PM (has caveolin)
Planar lipid raft – in neurons (has flotillin)

Caveolin and Flotillin recruit signalling proteins
- neurotransmitter binds G-protein coupled receptor –> effector
- PROMOTED or DAMPENED

Question 15

What are 2 diseases related to lipid rafts?

Answer 15

Alzheimer’s
- platform for amyloid-β to aggregate — kill neuron
Prion Disease
- normal prion protein convert to abnormal prion protein in lipid rafts

Question 16

How do lipid rafts associate with cytoskeleton?

Answer 16

• tight junctions (raft associated)
• adherens junction (not raft associated) – short TMD
• desmosome (raft associated) – long TMD