Cell Biology Lecture #23 notes p.477-491 Lipid Bilayer and Membrane Proteins Chapter 10

Membranes = "Compartmentalization" Nucleus, E.R., Golgi, organelles, etc.

Micelles, liposomes, black membranes, mycoplasmas as models.

Phospholipids, cholesterol, glycolipids = 3 major classes of membrane lipids.

Ion gradient for energy, fluid mosaic for concentration of reactants, receptors, ion gradients, etc.

5nm thick "fat sandwich" 50% amphipathic lipid, almost 50% protein. Permeability barrier.

One saturated, one unsaturated "tail". No "edge" to fat sandwich, so, self-sealing. (Injectable)

Micelles, liposomes, and "black membranes". Nitroxyl + ESR: "flip=flop" 1X/month.

Proteins and lipids slide sideways , rotate in "lipid sea". Synthesis in cytosolic ER face + phospholipid translocators (which cause assymetry of lipids).

Short chains, unsaturations = lower phase transitions(crystal), so bacteria adjust with low temp.

Cholesterol decreases permeability, inhibits phase transitions (eucaryotes). Cell wall helps bacteria, so, strength not essential.

4 mammalian phospholipids: phosphatidylcholine, sphingomyelin, phosphatidylserine(net negative charge), phosphatidylethanolamine. Some proteins require adjacent lipid(s)

Glycolipids (5% of lipids) on noncytoplasmic ½ of membrane, sugars added in Golgi lumen.

Glycolipid functions not understood, but may = receptors (cholera toxin example).

Membrane proteins = 25-75 % of membrane mass. Oligosaccharides attached.

"In natural states, all bacteria have a glycocalyx."

Proteins bind 6 ways to membranes; transmembrane amphipathics (alpha helix, beta barrel), attached to outside (prenyl group), attached to inside, bound to other proteins, etc....

Hydropathy plots. Triton X-100 vs. SDS (PAG electrophoresis)

RBC Ghosts, leaky ghosts, right-side out and inside-out ghosts, and their uses