CSF CH 10A: Lipid Bilayer

What properties do amphipathic lipids have that allow them to become bilayers, micelles, and liposomes

-nonpolar tail and polar head

-associate in “like” environments

hydrophobic portion of lipid

any part that has nonpolar bonds

hydroohilic portion of a lipid

bonds with large EN differences

Phosphatidylethanolamine (PE)=internal

Phosphatidylserine (PS)= internal,negatively charged

Phosphatidylcholine (PC)= external

Sphingomyelin= external

3 factors that affect membrane fluidity

1. composition

2. length: short chains more fluid

3. temp: high temp more fluid

membrane composition 3 factors

1. cholesterol makes membraned more stiff; less fluid

2. sat. fatty acids make less fluid

3. unsat. fatty acids make more fluid

Lateral diffusion

movement within the plane of the leaflet

flexion

tails can flex and move

rotation

lipids can rotate

flip-flop

lipids switch to diff leaflet sides (need help of flippases, scramblases, and phospholipid translocases)

2 reasons asymmetry matters

1. membrane change: PS presense on extracellular side causes cell death

2. cell signaling: PS and PI (also on cytosolic side) bind intracellular signaling proteins

lipid aggregation/lipid rafts

-rafts form in areas of greater fluidity (more sat. lipids)

-attract transmembrane proteins with linger hydrophobic transmembrane signaling

-important for cell signaling

components of lipid rafts

-cholesterol

-sat hydrocarbons

-glycolipids

(carbohydrate groups always on non-cytosolic side of membrane)

lipid droplet formation from interleaflet space of ER membrane

lipid droplet: storage for excess lipid where they can be retrived as building blocks for membrane sysnthesis or a food source fueling metabolic energy generation

-surrounded by phospholipid bilayer