lipid membranes Flashcards
what are membranes? what do they do (generally speaking)?
Proteins associated with lipid bilayers, all cells have membranes separate cell from its surroundings regulate entry/exit from cells divide internal space into compartments cell-cell communication
what is a micelle?
an arrangement of wedge shaped (single tailed) fatty acids where the hydrophobic tails congregate together to increase hydrophobic interactions. The result is an enclosed sphere with tails inside and heads outside.
what makes up a bilayer?
two leaflets of lipid monolayers. Each leaflet is made up of cylindrical (two tailed) fatty acids arranged with hydrophobic tails packed together inside and hydrophilic heads together outside.
what is a vesicle (liposome)?
small bilayers will spontaneously seal into spherical vesicles with an aqueous cavity in the middle that is able to carry molecules
functions of membranes
define cell boundaries allow import/export (selectively) retain metabolites and ions within cell sense external signals and transmit info into cell provide compartmentalization within cell produce/transmit nerve signals store energy as a proton gradient support ATP synthesis
common features of membranes
sheet-like flexible structure, 3-10 nm thick
structure is composed of two leaflets of lipids
form spontaneously in aqueous solution (stabilized by non covalent forces especially hydrophobic effect)
protein molecules span the bilayer
asymmetric with lipids preferably outside/inside
electrically polarized
fluid structures, lipids freely move laterally
what is the fluid mosaic model?
lipids form a viscous, 2D solvent into which proteins are integrated, often spanning the bilayer. peripheral proteins are weakly associated and can be removed easily
is lipid composition of membranes always the same?
no. composition varies in different organisms, tissues, and organelles. ratio of lipid to protein, type of phospholipid, and abundance/type of sterols varies
which lipids are found on which leaflets?
phosphatidylethanolamine and phosphatidylserine are inner monolayer and phosphatidylcholine and sphingomyelin are outer monolayer.
what does phosphatidylserine in the outer monolayer mean?
it has a special meaning in platelets where it activates blood clotting. in other cells it marks the cell for destruction.
what are the functions of proteins in membranes?
receptors
channels, gates, pumps
enzymes
what are the three types of proteins?
peripheral
GPI anchored
integral
how can you determine what type of protein a membrane protein is?
by what process is needed to remove it from the membrane
peripheral: removed by disrupting ionic interactions with high salt or change in pH
integral: removed by detergents that disrupt the membrane (lipids still associated)
GPI anchored: phospholipases cut protein from anchor
what are peripheral proteins? how do they interact with the membrane?
they associate with the polar head groups of membranes loosely through ionic interactions with lipids or integral proteins.
what are integral membrane proteins? how do they interact with the membrane?
they span a large part of the membrane (entire membrane = transmembrane protein). they are tightly associated with the membrane, protein hydrophobic stretches interact with hydrophobic membrane