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17 Cards in this Set

  • Front
  • Back
Function of membranes
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
Fluid mosaic model
Membrane proteins "floatin" in sea os phospholipids
Properties of fluid membranes
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
Outer leaflet
Inner leaflet
Phosphatidylserine (-)
What does cholesterol do?
Increases membrane packing
Derived from sphingosine, polar head group is carbohydrate. ONLY outer leaflet.

Galactocerebroside: main component of myelin sheath

Ganglioside: Common, functions poorly understood.
Lipid bi-layer properties
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.
Lipid rafts
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.
Alzheimer's and lipid rafts
Abnormal cholesterol metabolism in brain = abnormal lipid raft = generation of amyloid-beta peptide
Prion diseases (Creutzfeldt-Jacob) and lipid rafts
Lipid rafts may provide necessary enviroment to convert normal prion protein to infectious form.
Integral membrane protein
Require disruption of lipid bilayer to release from the membrane.

Transmembrane and covalently attached proteins.
Peripheral membrane protein
Can be removed from membrane by gentle extraction (change in pH, salt concentration)

Generally non-covalent interactions with other membrane proteins.
Receptors for chemical messages
Transmembrane proteins. Extracellular binds to ligand, intracellular initiates response.
Receptors for steroid hormones
Steroids are lipid soluable and can diffuse through plasma membrane are cytosolic proteins.
Signal transduction
Mechanism by which an extracellular chemical messenger is interpreted into an intracellular response.
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)