Plasma Membrane & Plant Cell Wall
where are peripheral proteins found
bound to membrane surface (on top of the lipid heads)
what function does asymmetry between leaflets in the plasma membrane serve?
electrochemical gradient --> important for signal transduction and transport of ions (negatively charged lipids on inner membrane)
what is lateral diffusion?
phospholipids on the same leaflet can switch places with each other (rarely flip flop between layers bc requires energy)
what are black membranes
planar lipid bilayers that form across a hole in partition b/w two aqueous places
main component of cell membrane
phospholipids and proteins
function of sterols
adds rigidity/stiffness to the membrane --> helps w/ structural integrity of plasma membrane warm temps: provides stiffness by preventing membrane from becoming too fluid low temps: keeps phospholipids from packing too tightly bc the sterols get in the way
what is pectin, where is it and what is its function
carbohydrates that form gel --> provide resistance to compression interwoven in cell wall w/ cellulose
what is the major component of the cell wall?
cellulose
what is the major sterol in animal cell membranes?
cholesterol
turgor pressure's role in cell development
driving force for cell expansion during growth
fluid mosaic model of plasma membrane
fluid: lateral diffusion of components in a leaflet mosaic: asymmetry, membrane is made up of clusters of diff types of molecules (discontinuous, not uniform)
what is the function of lignin
hard, waterproof filter --> cellulose is hydrophilic, would let water in
what is the only type of molecule that can pass thru the plasma membrane freely?
hydrophobic molecules
where are sterols located?
in between lipids in the bilayer
is the fluid mosaic model referring to an individual leaflet or the entire bilayer?
leaflet --> if you look down at the outer face of the membrane there are areas that are more abundant in one component than others ("neighborhoods")
which type of phospholipid is unique and why? (think charge)
phosphatidylserine has a net negative charge
lipid raft
low-density microdomains of plasma membrane rich in cholesterol and sphingolipids --> parts stick out far bc long tails so it looks like a raft NOT floating on the surface!
where are integral proteins found
membrane interior can span both leaflets in the transmembrane region could be anchored into 1 leaflet in b/w two lipids
what is the function of membrane proteins?
molecular transport, signal transduction, anchorage to cytoskeleton
can water pass thru cell membrane?
no --> it's polar so it can interact w the polar head of the phospholipid but it can't cross the inner region of hydrophobic tails
is energy needed for the membrane to self-assemble?
no additional energy input needed (assembly happens automatically)
can charged molecules or ions readily diffuse through the plasma membrane?
no bc charged molecules interact w polar regions (aka the phospholipid heads)
can glucose pass thru the membrane?
no because it has a lot of -OH groups which make it polar
is the plasma membrane symmetrical?
no; the inner and outer leaflets have diff distributions of types of phospholipids (this is not what the fluid mosaic model is referring to)
difference in charge between the leaflets
only the inner leaflet has negatively charged phospholipids
where is the plant cell wall located?
outside of plasma membrane of a plant cell (completely separate from plasma membrane)
Structure of a phospholipid
polar head group, 2 non-polar hydrocarbon tails -1 tail is saturated (no double bonds) so it's straight -1 tail is unsaturated (cis double bond) so it's bent
what properties of cellulose are important for cell wall?
provides tensile strength comparable to steel --> prevents cell from being stretched
what is the plasma membrane
regulated cell boundary: allows certain things to pass
structure of sterols
rigid ring structure polar head - fused rings - hydrocarbon tail
how does phospholipid structure affect fluidity of the membrane?
since one tail has cis double bonds, it is kinked --> phospholipids can't pack tightly --> increases fluidity
what are liposomes
spherical vesicles with a lipid bilayer --> spontaneous assembly
why does the bilayer form a sphere?
starts as planar but the non-polar tails on the edge interact w water (energetically unfavorable) --> folds into a sphere so that no tails are touching the water (energetically favorable)
turgor pressure
structural rigidity of cell wall allows for large internal pressure --> when cell has a lot of solutes, water flows in via osmosis
difference in symmetry b/w plasma membrane and ER membrane?
the plasma membrane is asymmetric; the ER membrane is symmetric
in what type of environment is turgor pressure highest?
when the extracellular environment is hypotonic
can membranes self-assemble and why?
yes bc of their amphiphilic nature --> polar heads associate w/ water, non-polar tails associate w/ each other on the inside
can steroids pass thru cell membrane?
yes because they are hydrophobic