cell membrane (bio week 3)

how do phospholipids form bilayers

nonpolar tails are shielded from aqueous environment (hydrophobic)

micelle vs bilayer

small and single tail vs large and two tails

why cant triglycerides form membranes

largely non polar (no hydrophilic properties)

membrane formation with other lipids

long hydrocarbon tail allows insert of lipids (such as cholesterol) into the bilayers and hydroxyl group of lipids interact with polar head groups of phospholipids influencing membrane rigidity

lipid bilayers are selectively permeable meaning

only some substance can get across

membrane permeability is determined by

chemistry of crossing substance and lipids in membrane, presence of transport proteins

pass easily

small nonpolar molecules (steroid hormones)

slowly pass

very small polar, uncharged

cannot pass

macromolecules (ions/charged/polar uncharged)

saturated fatty acids permeability

less permeable (stronger VDW forces/surface contact)

unsaturated and saturated permeability

more permeable

longer hydrocarbon tails

more surface contact and less permeable

simple diffusion

substances diffuse through membrane from high to low concentration (down/with gradient)

osmosis

diffusion of water across a membrane (moves to area of higher solute to even out solute on either side of membrane)

net movement of water

moves both ways

water pass

small and polar uncharged so passes slowly

high solute outside cell

hypertonic solution, water moves out into solution

high solute inside cell

hypotonic, water moves into cell