Cell Biology: Cell Membranes

Front 1

Function of membranes

Back 1

1. Maintaining structural integrity
2. Control passage of molecules
3. Regulating cell-cell interactions
4. Recognition of antigens, foreign cells, neighboring cells via recptors
5. Establishing transport systems for various molecules
6. Transducing extracellular signals into cellular responses

Front 2

Fluid mosaic model

Back 2

Membrane proteins "floatin" in sea os phospholipids

Front 3

Properties of fluid membranes

Back 3

1. Uniform distribution can be acomplished via insertion at localized sites
2. Membranes can reseal
3. Receptor aggregation at localized sites is possible
4. No flip-flopping

Front 4

Outer leaflet

Back 4

Phosphatidylcholine
Sphingomyelin

Front 5

Inner leaflet

Back 5

Phosphatidylethanolamine
Phosphatidylserine (-)
Phosphatidylinositol

Front 6

What does cholesterol do?

Back 6

Increases membrane packing

Front 7

Glycolipids

Back 7

Derived from sphingosine, polar head group is carbohydrate. ONLY outer leaflet.

Galactocerebroside: main component of myelin sheath

Ganglioside: Common, functions poorly understood.

Front 8

Lipid bi-layer properties

Back 8

Polar head groups, non-polar tails.

Outer and inner different composition.

Weakly permeable to water. Very permeable to O2, CO2. Not permeable to macromolecules. Limited permeability to ions.

Appears trilaminar under electron microsocpe (interaction of electron0dense stain osmium tetroxide with polar headgroups of membrane lipids but not with central hydrophobic portion of bilayer.

Front 9

Lipid rafts

Back 9

Microdomains with saturated phospholipids, cholestero, glycolipids, and few proteins (including caveolin). Membrane thicker, proteins restricted from lateral movement.

Functions in T-cell receptor signaling, nutrient absorption in intestine, endocytosis.

Front 10

Alzheimer's and lipid rafts

Back 10

Abnormal cholesterol metabolism in brain = abnormal lipid raft = generation of amyloid-beta peptide

Front 11

Prion diseases (Creutzfeldt-Jacob) and lipid rafts

Back 11

Lipid rafts may provide necessary enviroment to convert normal prion protein to infectious form.

Front 12

Integral membrane protein

Back 12

Require disruption of lipid bilayer to release from the membrane.

Transmembrane and covalently attached proteins.

Front 13

Peripheral membrane protein

Back 13

Can be removed from membrane by gentle extraction (change in pH, salt concentration)

Generally non-covalent interactions with other membrane proteins.

Front 14

Receptors for chemical messages

Back 14

Transmembrane proteins. Extracellular binds to ligand, intracellular initiates response.

Front 15

Receptors for steroid hormones

Back 15

Steroids are lipid soluable and can diffuse through plasma membrane are cytosolic proteins.

Front 16

Signal transduction

Back 16

Mechanism by which an extracellular chemical messenger is interpreted into an intracellular response.

Front 17

Glycocalyx

Back 17

Carbohydrate rich region on external side of plasma membrane. Formed primarily from carb moieties of membrane glycolipids, glycoproteins, and secreted proteoglycans. Functions to bind food molecules in intestines, recognition of other cells, protection of cells from harsh enviroments (GI tract)