membranes, diffusion + osmosis

fluid mosaic model arrangement?

• bilayer containing intrinsic proteins (channel + carrier)

• extrinsic proteins on membrane surface e

• glyco lipids+proteins on exterior surface

• sometimes cholesterol on fatty acid tails

role of cholesterol in cell membrane?

• restricts movement of other molecules making up membrane

• decreasing fluidity + permeability; making it more rigid

adaptations of membrane?

• fluid bilayer - membrane can bend for vesicle formation/phagocytosis

• glycol lipids/proteins act as receptors → cell recognition/signalling

simple diffusion?

area high conc → area low conc, down conc gradient

across bilayer

passive, only KE required

what type of molecules move across membrane via simple diffusion?

lipid soluble/small substances

why does phospholipid bilayer restrict polar + large substances?

repelled by hydrophobic fatty acid tails

facilitated diffusion?

area high conc → area low conc down conc gradient

via specific channel/carrier proteins whose shape determines what substance is transported

passive, only KE required

what type of molecules move across membrane via facilitated diffusion?

polar/large substances

channel proteins?

• allow polar substances

• have a hydrophilic pore filled with water

• may be gated

carrier proteins?

• allow larger substances

• complementary substances attach to binding sites

• proteins changes shape to transport substance

osmosis?

• water diffuses/moves

• from area of high WP → low WP, down WP gradient

• via partially permeable membrane

• passive, only KE required

how is the movement of substances across cell membranes affected by membrane structure?

• phospholipid bilayer prevents diffusion of polar/charged/lipid-insoluble substances

• channel proteins allow for their diffusion

• carrier proteins allow for active transport

• channel/carrier proteins allow for facilitated diffusion

• shape of channel/carrier determine which substances move, and amount of them + membrane SA determines how much moves

• cholesterol affect fluidity