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28 Cards in this Set

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selective permeability
allows some substances to pass more easily than others -
b/c of hydrophobic core
amphipathic
has both hydrophillic and hydrophobic regions
currently accepted membrane model
fluid mosaic model
-phospholipid bilayer
-embedded proteins, which are also amphipathic
-fluid - able to move
membranes are held together by...
hydrophobic interactions in the core, allows phospholipids to move laterally quite rapidly, but rarely do they flip-flop; larger membrane proteins may drift but slowly
membrane fluidity
-influenced by temp.
-as temp. decreases the membrane becomes less fluid and can eventually solidify(not good)
-presence of unsaturated fatty acid chains in membrane phospholipids make membranes more fluid
-cholesterol resticts fluidity at warmer temperatures but prevent solidification at warmer temperatures
peripheral proteins
-not embedded
-loosely bounded to the surface
integral proteins
-penetrate the hydrophobic core, span the entire membrane
-they also have a hydrophobic core; usually made of alpha helices
-where they are in contact with the aqueous environment, they are hydrophillic
membrane sidedness
-membranes have distinct inside and outside faces
-layers may differe in lipid composition and proteins have specific directions
-outer surface has carbohydrates
-means the ER must synthesize the membrane from the inside out
functions of membrane proteins
-transport
-enzymatic activity
-signal transduction
-intracellular jioning
-cell to cell recognition
-attachment to cytoskeleton/extracellular matrix
glycolipid
-sugar and lipid
glycoprotein
-sugar attached to membrane protein
oligosaccharide
membrane carbohydrates usually branched these --simple sugars
permeability
-depends on molecules interaction with the hydrophobic core
-non-polar/hydrophobic molecules pass easily
-polar/hydrophillic/ions have more difficulty passing
transport proteins
-these proteins carry out facilitated diffusion
-allow specific ions/polar molecules to cross the membrane through itself
-every transport protien is specific to one kind of substance
diffusion
tendency of molecules to spread out in the available space
passive transport
-diffusion of a substance across a biological membrane
-w/concentration gradient
-no energy need, includes transport proteins
Osmosis
passive transport of waterin selectively permeable membranes
tonicty
hypertonic-more solute concentration
isotonic - equal solute concentration
hypotonic - lower solute concentration
reactions to tonicity
hypertonic - cells will lose too much water and shrivel and die, plasmolysis in plants
isotonic- no net gain of water(plants are flaccid)
hypotonic - cell will take on too much water and animal cells lyse (burst) but plant cell walls exert a pressure back on the water and the cell becomes turgid(good!)
aquaporins
facilitate massive amounts of diffusion of water
gated channels
-open or close dependingon the presense or absence of a physical or chemical stimulus
active transport
-cell must spend energy to transport substances against their gradient
Energy supplied by...
phosphorylation of ATP
exocytosis
transport vesicle from golgi fuses with the membrane and spills contents
endocytosis
brings in large molecules which couldn't otherwise cross the membrane
phagocytosis
-"cellular eating"
-large "food" particles engulfed by pseudopodia
pinocystosis
-"cellular drinking"
-vesicle around droplet of extracellular fluid
-non-specific
-used to get ions in the surrounding ECF
receptor-mediated endocytosis
-ligands bind to protein receptors which trigger the formation of a vesicle
-allows cells to acquire bulk quantities of specific materials