Membranes

What are biological membranes made up of?

amphipathic lipids

What are examples of the lipids that make up biological membranes?

glycerophospholipids, sphingolipids, cholesterol

micelle

spherical aggregate of amphipathic molecules

Why do micelles form?

exposing hydrophobic molecules to water is unfavorable

What does water form around hydrophobic groups?

clathrates

What are clathrates?

cage-like chemical structure

What is micelle formation primarily driven by?

hydrophobic effect and entropy

Why are clathrates entropically unfavorable?

water molecules more organized

What is the Critical Micelle Concentration (CMC)?

The minimum concentration of an amphiphile required for spontaneous micelle formation

What do amphiphiles do below the CMC?

form a monolayer

Why don't Triacylglycerols form micelles?

mostly nonpolar, no hydrophilic head

Why do fatty acids and detergents NOT form membranes?

large hydrophilic head causes tapered geometry, which favors micelle

liposome

closed, self-sealing, water-filled vesicle surrounded by a single lipid bilayer.

Whats the ∆G for liposome formation?

G < 0

Why is liposome formation spontaneous?

The hydrophobic effect increases the entropy of water

unilamellar vesicles

liposome where one bilayer surrounding water

multilamellar vesicles

liposome where multiple bilayer surrounding water

What can passively diffuse through lipid bilayers?

small hydrophobic molecules

What are lipid bilayers incredibly impermeable to?

ionic and polar substances

Lateral diffusion

movement of a lipid within the same leaflet of the membrane

Transverse diffusion

flip flop of lipid to other leaflet

What enzymes facilitate transverse diffusion?

flippases, floppases, scramblases

What does the Frye-Ediden experiment demonstrate?

fluidity of membranes and lateral mobility

What reduces the fluidity of the membrane at high temperatures?

cholesterol