3/30 lecture - phospholipids + membranes

membranes contain + delimit cells

to separate the extracellular env from the intracellular one, membranes need to be WATER IMPERMEABLE

intracellular membranes

water impermeable, each organelle has a specific function regulated by diff proteins + need membranes to separate them from the rest of cell

semi-permeable membrane

though impermeable to water, membranes can carry out specific functions; made of lipids + proteins

lipids in membrane

water impermeable + separate compartments

proteins in membrane

“embedded", allow the comms between compartments, ex: exchange of molecules

hydrophilic head of fatty acid

makes electrostatic interactions w/ H2O

hydrophobic tails

make hydrophobic interactions w/ one another, creating env impermeable to H2O

amphiphatic molecule

one side is hydrophilic (polar), the other side is hydrophobic (nonpolar)

how can amphipatic molecules arrange themselves in H2O env in and out of the cell?

amphipatic molecules spontaneously form a bilayer in water (assemble feet-to-feet)

what causes the kink in hydrocarbon tail of phosphatidylcoline?

double bond

what is the best shape for membranes in order to minimize H2O + lipid interactions?

spontaneous sealed compartments formed by phospholipid bilayers (avoid free edges exposed to water) → membrane flexibility

liposomes

pure phospholipids organize in closed structures in water

fluidity

ability of lipids within a membrane to rearrange within their own monolayer

kink

unsaturated (fewer hydrogen molecules) chains to reduce hydrophobic interactions

fluidity depends on?

hydrophobic interactions between lipids in one layer:

1. length of fatty acids in lipids → longer = more hydrophobic interactions = less fluidity

2. # unsaturated fatty acids/double bonds → higher # double bonds = less hydrophobic interactions = more fluidity

what hemps stiffen the cell membrane in animal cells?

cholesterol

ER membrane synthesis via scramblases

1. phospholipid synthesis adds to cytosolic half of bilayer

2. scramblase catalyzes transfer of lipids from one monolayer to the other

3. symmetric growth of both halves of bilayer

is lipid bilayer asymmetrical?

yes, asymmetrical distribution of phospholipids + glycolipids in the membrane

what controls the distribution of phospholipids within the two layers of a membrane?

flippases, enzymes (proteins) found in the Golgi compartment reorganize phospholipids across the two sides of membrane from ER → cell membrane